xref: /btstack/src/hci.c (revision e35edcc121f2d8c6e357d758e82968ac2e1b79de)

/*
 * Copyright (C) 2014 BlueKitchen GmbH
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 * 4. Any redistribution, use, or modification is done solely for
 *    personal benefit and not for any commercial purpose or for
 *    monetary gain.
 *
 * THIS SOFTWARE IS PROVIDED BY BLUEKITCHEN GMBH AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MATTHIAS
 * RINGWALD OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
 * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * Please inquire about commercial licensing options at
 * [email protected]
 *
 */

/*
 *  hci.c
 *
 *  Created by Matthias Ringwald on 4/29/09.
 *
 */

#include "btstack-config.h"

#include "hci.h"
#include "gap.h"

#include <stdarg.h>
#include <string.h>
#include <stdio.h>

#ifndef EMBEDDED
#ifdef _WIN32
#include "Winsock2.h"
#else
#include <unistd.h> // gethostbyname
#endif
#include <btstack/version.h>
#endif

#include "btstack_memory.h"
#include "debug.h"
#include "hci_dump.h"

#include <btstack/linked_list.h>
#include <btstack/hci_cmds.h>

#define HCI_CONNECTION_TIMEOUT_MS 10000

#define HCI_INTIALIZING_SUBSTATE_AFTER_SLEEP 11

#ifdef USE_BLUETOOL
#include "../platforms/ios/src/bt_control_iphone.h"
#endif

static void hci_update_scan_enable(void);
static gap_security_level_t gap_security_level_for_connection(hci_connection_t * connection);
static void hci_connection_timeout_handler(timer_source_t *timer);
static void hci_connection_timestamp(hci_connection_t *connection);
static int  hci_power_control_on(void);
static void hci_power_control_off(void);
static void hci_state_reset();

// the STACK is here
#ifndef HAVE_MALLOC
static hci_stack_t   hci_stack_static;
#endif
static hci_stack_t * hci_stack = NULL;

// test helper
static uint8_t disable_l2cap_timeouts = 0;

/**
 * create connection for given address
 *
 * @return connection OR NULL, if no memory left
 */
static hci_connection_t * create_connection_for_bd_addr_and_type(bd_addr_t addr, bd_addr_type_t addr_type){
    log_info("create_connection_for_addr %s", bd_addr_to_str(addr));
    hci_connection_t * conn = btstack_memory_hci_connection_get();
    if (!conn) return NULL;
    memset(conn, 0, sizeof(hci_connection_t));
    BD_ADDR_COPY(conn->address, addr);
    conn->address_type = addr_type;
    conn->con_handle = 0xffff;
    conn->authentication_flags = AUTH_FLAGS_NONE;
    conn->bonding_flags = 0;
    conn->requested_security_level = LEVEL_0;
    linked_item_set_user(&conn->timeout.item, conn);
    conn->timeout.process = hci_connection_timeout_handler;
    hci_connection_timestamp(conn);
    conn->acl_recombination_length = 0;
    conn->acl_recombination_pos = 0;
    conn->num_acl_packets_sent = 0;
    conn->le_con_parameter_update_state = CON_PARAMETER_UPDATE_NONE;
    linked_list_add(&hci_stack->connections, (linked_item_t *) conn);
    return conn;
}


/**
 * get le connection parameter range
*
 * @return le connection parameter range struct
 */
le_connection_parameter_range_t gap_le_get_connection_parameter_range(){
    return hci_stack->le_connection_parameter_range;
}

/**
 * set le connection parameter range
 *
 */

void gap_le_set_connection_parameter_range(le_connection_parameter_range_t range){
    hci_stack->le_connection_parameter_range.le_conn_interval_min = range.le_conn_interval_min;
    hci_stack->le_connection_parameter_range.le_conn_interval_max = range.le_conn_interval_max;
    hci_stack->le_connection_parameter_range.le_conn_interval_min = range.le_conn_latency_min;
    hci_stack->le_connection_parameter_range.le_conn_interval_max = range.le_conn_latency_max;
    hci_stack->le_connection_parameter_range.le_supervision_timeout_min = range.le_supervision_timeout_min;
    hci_stack->le_connection_parameter_range.le_supervision_timeout_max = range.le_supervision_timeout_max;
}

/**
 * get hci connections iterator
 *
 * @return hci connections iterator
 */

void hci_connections_get_iterator(linked_list_iterator_t *it){
    linked_list_iterator_init(it, &hci_stack->connections);
}

/**
 * get connection for a given handle
 *
 * @return connection OR NULL, if not found
 */
hci_connection_t * hci_connection_for_handle(hci_con_handle_t con_handle){
    linked_list_iterator_t it;
    linked_list_iterator_init(&it, &hci_stack->connections);
    while (linked_list_iterator_has_next(&it)){
        hci_connection_t * item = (hci_connection_t *) linked_list_iterator_next(&it);
        if ( item->con_handle == con_handle ) {
            return item;
        }
    }
    return NULL;
}

/**
 * get connection for given address
 *
 * @return connection OR NULL, if not found
 */
hci_connection_t * hci_connection_for_bd_addr_and_type(bd_addr_t * addr, bd_addr_type_t addr_type){
    linked_list_iterator_t it;
    linked_list_iterator_init(&it, &hci_stack->connections);
    while (linked_list_iterator_has_next(&it)){
        hci_connection_t * connection = (hci_connection_t *) linked_list_iterator_next(&it);
        if (connection->address_type != addr_type)  continue;
        if (memcmp(addr, connection->address, 6) != 0) continue;
        return connection;
    }
    return NULL;
}

static void hci_connection_timeout_handler(timer_source_t *timer){
    hci_connection_t * connection = (hci_connection_t *) linked_item_get_user(&timer->item);
#ifdef HAVE_TIME
    struct timeval tv;
    gettimeofday(&tv, NULL);
    if (tv.tv_sec >= connection->timestamp.tv_sec + HCI_CONNECTION_TIMEOUT_MS/1000) {
        // connections might be timed out
        hci_emit_l2cap_check_timeout(connection);
    }
#endif
#ifdef HAVE_TICK
    if (embedded_get_ticks() > connection->timestamp + embedded_ticks_for_ms(HCI_CONNECTION_TIMEOUT_MS)){
        // connections might be timed out
        hci_emit_l2cap_check_timeout(connection);
    }
#endif
    run_loop_set_timer(timer, HCI_CONNECTION_TIMEOUT_MS);
    run_loop_add_timer(timer);
}

static void hci_connection_timestamp(hci_connection_t *connection){
#ifdef HAVE_TIME
    gettimeofday(&connection->timestamp, NULL);
#endif
#ifdef HAVE_TICK
    connection->timestamp = embedded_get_ticks();
#endif
}


inline static void connectionSetAuthenticationFlags(hci_connection_t * conn, hci_authentication_flags_t flags){
    conn->authentication_flags = (hci_authentication_flags_t)(conn->authentication_flags | flags);
}

inline static void connectionClearAuthenticationFlags(hci_connection_t * conn, hci_authentication_flags_t flags){
    conn->authentication_flags = (hci_authentication_flags_t)(conn->authentication_flags & ~flags);
}


/**
 * add authentication flags and reset timer
 * @note: assumes classic connection
 */
static void hci_add_connection_flags_for_flipped_bd_addr(uint8_t *bd_addr, hci_authentication_flags_t flags){
    bd_addr_t addr;
    bt_flip_addr(addr, *(bd_addr_t *) bd_addr);
    hci_connection_t * conn = hci_connection_for_bd_addr_and_type(&addr, BD_ADDR_TYPE_CLASSIC);
    if (conn) {
        connectionSetAuthenticationFlags(conn, flags);
        hci_connection_timestamp(conn);
    }
}

int  hci_authentication_active_for_handle(hci_con_handle_t handle){
    hci_connection_t * conn = hci_connection_for_handle(handle);
    if (!conn) return 0;
    if (conn->authentication_flags & LEGACY_PAIRING_ACTIVE) return 1;
    if (conn->authentication_flags & SSP_PAIRING_ACTIVE) return 1;
    return 0;
}

void hci_drop_link_key_for_bd_addr(bd_addr_t *addr){
    if (hci_stack->remote_device_db) {
        hci_stack->remote_device_db->delete_link_key(addr);
    }
}

int hci_is_le_connection(hci_connection_t * connection){
    return  connection->address_type == BD_ADDR_TYPE_LE_PUBLIC ||
    connection->address_type == BD_ADDR_TYPE_LE_RANDOM;
}


/**
 * count connections
 */
static int nr_hci_connections(void){
    int count = 0;
    linked_item_t *it;
    for (it = (linked_item_t *) hci_stack->connections; it ; it = it->next, count++);
    return count;
}

/**
 * Dummy handler called by HCI
 */
static void dummy_handler(uint8_t packet_type, uint8_t *packet, uint16_t size){
}

uint8_t hci_number_outgoing_packets(hci_con_handle_t handle){
    hci_connection_t * connection = hci_connection_for_handle(handle);
    if (!connection) {
        log_error("hci_number_outgoing_packets: connection for handle %u does not exist!", handle);
        return 0;
    }
    return connection->num_acl_packets_sent;
}

uint8_t hci_number_free_acl_slots_for_handle(hci_con_handle_t con_handle){

    int num_packets_sent_classic = 0;
    int num_packets_sent_le = 0;

    bd_addr_type_t address_type = BD_ADDR_TYPE_UNKNOWN;

    linked_item_t *it;
    for (it = (linked_item_t *) hci_stack->connections; it ; it = it->next){
        hci_connection_t * connection = (hci_connection_t *) it;
        if (connection->address_type == BD_ADDR_TYPE_CLASSIC){
            num_packets_sent_classic += connection->num_acl_packets_sent;
        } else {
            num_packets_sent_le += connection->num_acl_packets_sent;
        }
        // ignore connections that are not open, e.g., in state RECEIVED_DISCONNECTION_COMPLETE
        if (connection->con_handle == con_handle && connection->state == OPEN){
            address_type = connection->address_type;
        }
    }

    int free_slots_classic = hci_stack->acl_packets_total_num - num_packets_sent_classic;
    int free_slots_le = 0;

    if (free_slots_classic < 0){
        log_error("hci_number_free_acl_slots: outgoing classic packets (%u) > total classic packets (%u)", num_packets_sent_classic, hci_stack->acl_packets_total_num);
        return 0;
    }

    if (hci_stack->le_acl_packets_total_num){
        // if we have LE slots, they are used
        free_slots_le = hci_stack->le_acl_packets_total_num - num_packets_sent_le;
        if (free_slots_le < 0){
            log_error("hci_number_free_acl_slots: outgoing le packets (%u) > total le packets (%u)", num_packets_sent_le, hci_stack->le_acl_packets_total_num);
            return 0;
        }
    } else {
        // otherwise, classic slots are used for LE, too
        free_slots_classic -= num_packets_sent_le;
        if (free_slots_classic < 0){
            log_error("hci_number_free_acl_slots: outgoing classic + le packets (%u + %u) > total packets (%u)", num_packets_sent_classic, num_packets_sent_le, hci_stack->acl_packets_total_num);
            return 0;
        }
    }

    switch (address_type){
        case BD_ADDR_TYPE_UNKNOWN:
            log_error("hci_number_free_acl_slots: handle 0x%04x not in connection list", con_handle);
            return 0;

        case BD_ADDR_TYPE_CLASSIC:
            return free_slots_classic;

        default:
           if (hci_stack->le_acl_packets_total_num){
               return free_slots_le;
           }
           return free_slots_classic;
    }
}

int hci_number_free_sco_slots_for_handle(hci_con_handle_t handle){
    int num_sco_packets_sent = 0;
    linked_item_t *it;
    for (it = (linked_item_t *) hci_stack->connections; it ; it = it->next){
        hci_connection_t * connection = (hci_connection_t *) it;
        num_sco_packets_sent += connection->num_sco_packets_sent;
    }
    if (num_sco_packets_sent > hci_stack->sco_packets_total_num){
        log_info("hci_number_free_sco_slots_for_handle: outgoing packets (%u) > total packets ()", num_sco_packets_sent, hci_stack->sco_packets_total_num);
        return 0;
    }
    return hci_stack->sco_packets_total_num - num_sco_packets_sent;
}

// new functions replacing hci_can_send_packet_now[_using_packet_buffer]
int hci_can_send_command_packet_now(void){
    if (hci_stack->hci_packet_buffer_reserved) return 0;

    // check for async hci transport implementations
    if (hci_stack->hci_transport->can_send_packet_now){
        if (!hci_stack->hci_transport->can_send_packet_now(HCI_COMMAND_DATA_PACKET)){
            return 0;
        }
    }

    return hci_stack->num_cmd_packets > 0;
}

int hci_can_send_prepared_acl_packet_now(hci_con_handle_t con_handle) {
    // check for async hci transport implementations
    if (hci_stack->hci_transport->can_send_packet_now){
        if (!hci_stack->hci_transport->can_send_packet_now(HCI_ACL_DATA_PACKET)){
            return 0;
        }
    }
    return hci_number_free_acl_slots_for_handle(con_handle) > 0;
}

int hci_can_send_acl_packet_now(hci_con_handle_t con_handle){
    if (hci_stack->hci_packet_buffer_reserved) return 0;
    return hci_can_send_prepared_acl_packet_now(con_handle);
}

int hci_can_send_prepared_sco_packet_now(hci_con_handle_t con_handle){
    if (hci_stack->hci_transport->can_send_packet_now){
        if (!hci_stack->hci_transport->can_send_packet_now(HCI_SCO_DATA_PACKET)){
            return 0;
        }
    }
    return hci_number_free_sco_slots_for_handle(con_handle) > 0;
}

int hci_can_send_sco_packet_now(hci_con_handle_t con_handle){
    if (hci_stack->hci_packet_buffer_reserved) return 0;
    return hci_can_send_prepared_sco_packet_now(con_handle);
}

// used for internal checks in l2cap[-le].c
int hci_is_packet_buffer_reserved(void){
    return hci_stack->hci_packet_buffer_reserved;
}

// reserves outgoing packet buffer. @returns 1 if successful
int hci_reserve_packet_buffer(void){
    if (hci_stack->hci_packet_buffer_reserved) {
        log_error("hci_reserve_packet_buffer called but buffer already reserved");
        return 0;
    }
    hci_stack->hci_packet_buffer_reserved = 1;
    return 1;
}

void hci_release_packet_buffer(void){
    hci_stack->hci_packet_buffer_reserved = 0;
}

// assumption: synchronous implementations don't provide can_send_packet_now as they don't keep the buffer after the call
int hci_transport_synchronous(void){
    return hci_stack->hci_transport->can_send_packet_now == NULL;
}

uint16_t hci_max_acl_le_data_packet_length(void){
    return hci_stack->le_data_packets_length > 0 ? hci_stack->le_data_packets_length : hci_stack->acl_data_packet_length;
}

static int hci_send_acl_packet_fragments(hci_connection_t *connection){

    // log_info("hci_send_acl_packet_fragments  %u/%u (con 0x%04x)", hci_stack->acl_fragmentation_pos, hci_stack->acl_fragmentation_total_size, connection->con_handle);

    // max ACL data packet length depends on connection type (LE vs. Classic) and available buffers
    uint16_t max_acl_data_packet_length = hci_stack->acl_data_packet_length;
    if (hci_is_le_connection(connection) && hci_stack->le_data_packets_length > 0){
        max_acl_data_packet_length = hci_stack->le_data_packets_length;
    }

    // testing: reduce buffer to minimum
    // max_acl_data_packet_length = 52;

    int err;
    // multiple packets could be send on a synchronous HCI transport
    while (1){

        // get current data
        const uint16_t acl_header_pos = hci_stack->acl_fragmentation_pos - 4;
        int current_acl_data_packet_length = hci_stack->acl_fragmentation_total_size - hci_stack->acl_fragmentation_pos;
        int more_fragments = 0;

        // if ACL packet is larger than Bluetooth packet buffer, only send max_acl_data_packet_length
        if (current_acl_data_packet_length > max_acl_data_packet_length){
            more_fragments = 1;
            current_acl_data_packet_length = max_acl_data_packet_length;
        }

        // copy handle_and_flags if not first fragment and update packet boundary flags to be 01 (continuing fragmnent)
        if (acl_header_pos > 0){
            uint16_t handle_and_flags = READ_BT_16(hci_stack->hci_packet_buffer, 0);
            handle_and_flags = (handle_and_flags & 0xcfff) | (1 << 12);
            bt_store_16(hci_stack->hci_packet_buffer, acl_header_pos, handle_and_flags);
        }

        // update header len
        bt_store_16(hci_stack->hci_packet_buffer, acl_header_pos + 2, current_acl_data_packet_length);

        // count packet
        connection->num_acl_packets_sent++;

        // send packet
        uint8_t * packet = &hci_stack->hci_packet_buffer[acl_header_pos];
        const int size = current_acl_data_packet_length + 4;
        hci_dump_packet(HCI_ACL_DATA_PACKET, 0, packet, size);
        err = hci_stack->hci_transport->send_packet(HCI_ACL_DATA_PACKET, packet, size);

        // done yet?
        if (!more_fragments) break;

        // update start of next fragment to send
        hci_stack->acl_fragmentation_pos += current_acl_data_packet_length;

        // can send more?
        if (!hci_can_send_prepared_acl_packet_now(connection->con_handle)) return err;
    }

    // done
    hci_stack->acl_fragmentation_pos = 0;
    hci_stack->acl_fragmentation_total_size = 0;

    // release buffer now for synchronous transport
    if (hci_transport_synchronous()){
        hci_release_packet_buffer();
    }

    return err;
}

// pre: caller has reserved the packet buffer
int hci_send_acl_packet_buffer(int size){

    // log_info("hci_send_acl_packet_buffer size %u", size);

    if (!hci_stack->hci_packet_buffer_reserved) {
        log_error("hci_send_acl_packet_buffer called without reserving packet buffer");
        return 0;
    }

    uint8_t * packet = hci_stack->hci_packet_buffer;
    hci_con_handle_t con_handle = READ_ACL_CONNECTION_HANDLE(packet);

    // check for free places on Bluetooth module
    if (!hci_can_send_prepared_acl_packet_now(con_handle)) {
        log_error("hci_send_acl_packet_buffer called but no free ACL buffers on controller");
        hci_release_packet_buffer();
        return BTSTACK_ACL_BUFFERS_FULL;
    }

    hci_connection_t *connection = hci_connection_for_handle( con_handle);
    if (!connection) {
        log_error("hci_send_acl_packet_buffer called but no connection for handle 0x%04x", con_handle);
        hci_release_packet_buffer();
        return 0;
    }
    hci_connection_timestamp(connection);

    // hci_dump_packet( HCI_ACL_DATA_PACKET, 0, packet, size);

    // setup data
    hci_stack->acl_fragmentation_total_size = size;
    hci_stack->acl_fragmentation_pos = 4;   // start of L2CAP packet

    return hci_send_acl_packet_fragments(connection);
}

// pre: caller has reserved the packet buffer
int hci_send_sco_packet_buffer(int size){

    // log_info("hci_send_acl_packet_buffer size %u", size);

    if (!hci_stack->hci_packet_buffer_reserved) {
        log_error("hci_send_acl_packet_buffer called without reserving packet buffer");
        return 0;
    }

    uint8_t * packet = hci_stack->hci_packet_buffer;
    hci_con_handle_t con_handle = READ_ACL_CONNECTION_HANDLE(packet);   // same for ACL and SCO

    // check for free places on Bluetooth module
    if (!hci_can_send_prepared_sco_packet_now(con_handle)) {
        log_error("hci_send_sco_packet_buffer called but no free ACL buffers on controller");
        hci_release_packet_buffer();
        return BTSTACK_ACL_BUFFERS_FULL;
    }

    // track send packet in connection struct
    hci_connection_t *connection = hci_connection_for_handle( con_handle);
    if (!connection) {
        log_error("hci_send_sco_packet_buffer called but no connection for handle 0x%04x", con_handle);
        hci_release_packet_buffer();
        return 0;
    }
    connection->num_sco_packets_sent++;

    hci_dump_packet( HCI_SCO_DATA_PACKET, 0, packet, size);
    return hci_stack->hci_transport->send_packet(HCI_SCO_DATA_PACKET, packet, size);
}

static void acl_handler(uint8_t *packet, int size){

    // log_info("acl_handler: size %u", size);

    // get info
    hci_con_handle_t con_handle = READ_ACL_CONNECTION_HANDLE(packet);
    hci_connection_t *conn      = hci_connection_for_handle(con_handle);
    uint8_t  acl_flags          = READ_ACL_FLAGS(packet);
    uint16_t acl_length         = READ_ACL_LENGTH(packet);

    // ignore non-registered handle
    if (!conn){
        log_error( "hci.c: acl_handler called with non-registered handle %u!" , con_handle);
        return;
    }

    // assert packet is complete
    if (acl_length + 4 != size){
        log_error("hci.c: acl_handler called with ACL packet of wrong size %u, expected %u => dropping packet", size, acl_length + 4);
        return;
    }

    // update idle timestamp
    hci_connection_timestamp(conn);

    // handle different packet types
    switch (acl_flags & 0x03) {

        case 0x01: // continuation fragment

            // sanity checks
            if (conn->acl_recombination_pos == 0) {
                log_error( "ACL Cont Fragment but no first fragment for handle 0x%02x", con_handle);
                return;
            }
            if (conn->acl_recombination_pos + acl_length > 4 + HCI_ACL_BUFFER_SIZE){
                log_error( "ACL Cont Fragment to large: combined packet %u > buffer size %u for handle 0x%02x",
                    conn->acl_recombination_pos + acl_length, 4 + HCI_ACL_BUFFER_SIZE, con_handle);
                conn->acl_recombination_pos = 0;
                return;
            }

            // append fragment payload (header already stored)
            memcpy(&conn->acl_recombination_buffer[HCI_INCOMING_PRE_BUFFER_SIZE + conn->acl_recombination_pos], &packet[4], acl_length );
            conn->acl_recombination_pos += acl_length;

            // log_error( "ACL Cont Fragment: acl_len %u, combined_len %u, l2cap_len %u", acl_length,
            //        conn->acl_recombination_pos, conn->acl_recombination_length);

            // forward complete L2CAP packet if complete.
            if (conn->acl_recombination_pos >= conn->acl_recombination_length + 4 + 4){ // pos already incl. ACL header

                hci_stack->packet_handler(HCI_ACL_DATA_PACKET, &conn->acl_recombination_buffer[HCI_INCOMING_PRE_BUFFER_SIZE], conn->acl_recombination_pos);
                // reset recombination buffer
                conn->acl_recombination_length = 0;
                conn->acl_recombination_pos = 0;
            }
            break;

        case 0x02: { // first fragment

            // sanity check
            if (conn->acl_recombination_pos) {
                log_error( "ACL First Fragment but data in buffer for handle 0x%02x, dropping stale fragments", con_handle);
                conn->acl_recombination_pos = 0;
            }

            // peek into L2CAP packet!
            uint16_t l2cap_length = READ_L2CAP_LENGTH( packet );

            // log_info( "ACL First Fragment: acl_len %u, l2cap_len %u", acl_length, l2cap_length);

            // compare fragment size to L2CAP packet size
            if (acl_length >= l2cap_length + 4){

                // forward fragment as L2CAP packet
                hci_stack->packet_handler(HCI_ACL_DATA_PACKET, packet, acl_length + 4);

            } else {

                if (acl_length > HCI_ACL_BUFFER_SIZE){
                    log_error( "ACL First Fragment to large: fragment %u > buffer size %u for handle 0x%02x",
                        4 + acl_length, 4 + HCI_ACL_BUFFER_SIZE, con_handle);
                    return;
                }

                // store first fragment and tweak acl length for complete package
                memcpy(&conn->acl_recombination_buffer[HCI_INCOMING_PRE_BUFFER_SIZE], packet, acl_length + 4);
                conn->acl_recombination_pos    = acl_length + 4;
                conn->acl_recombination_length = l2cap_length;
                bt_store_16(conn->acl_recombination_buffer, HCI_INCOMING_PRE_BUFFER_SIZE + 2, l2cap_length +4);
            }
            break;

        }
        default:
            log_error( "hci.c: acl_handler called with invalid packet boundary flags %u", acl_flags & 0x03);
            return;
    }

    // execute main loop
    hci_run();
}

static void hci_shutdown_connection(hci_connection_t *conn){
    log_info("Connection closed: handle 0x%x, %s", conn->con_handle, bd_addr_to_str(conn->address));

    run_loop_remove_timer(&conn->timeout);

    linked_list_remove(&hci_stack->connections, (linked_item_t *) conn);
    btstack_memory_hci_connection_free( conn );

    // now it's gone
    hci_emit_nr_connections_changed();
}

static const uint16_t packet_type_sizes[] = {
    0, HCI_ACL_2DH1_SIZE, HCI_ACL_3DH1_SIZE, HCI_ACL_DM1_SIZE,
    HCI_ACL_DH1_SIZE, 0, 0, 0,
    HCI_ACL_2DH3_SIZE, HCI_ACL_3DH3_SIZE, HCI_ACL_DM3_SIZE, HCI_ACL_DH3_SIZE,
    HCI_ACL_2DH5_SIZE, HCI_ACL_3DH5_SIZE, HCI_ACL_DM5_SIZE, HCI_ACL_DH5_SIZE
};
static const uint8_t  packet_type_feature_requirement_bit[] = {
     0, // 3 slot packets
     1, // 5 slot packets
    25, // EDR 2 mpbs
    26, // EDR 3 mbps
    39, // 3 slot EDR packts
    40, // 5 slot EDR packet
};
static const uint16_t packet_type_feature_packet_mask[] = {
    0x0f00, // 3 slot packets
    0xf000, // 5 slot packets
    0x1102, // EDR 2 mpbs
    0x2204, // EDR 3 mbps
    0x0300, // 3 slot EDR packts
    0x3000, // 5 slot EDR packet
};

static uint16_t hci_acl_packet_types_for_buffer_size_and_local_features(uint16_t buffer_size, uint8_t * local_supported_features){
    // enable packet types based on size
    uint16_t packet_types = 0;
    unsigned int i;
    for (i=0;i<16;i++){
        if (packet_type_sizes[i] == 0) continue;
        if (packet_type_sizes[i] <= buffer_size){
            packet_types |= 1 << i;
        }
    }
    // disable packet types due to missing local supported features
    for (i=0;i<sizeof(packet_type_feature_requirement_bit);i++){
        int bit_idx = packet_type_feature_requirement_bit[i];
        int feature_set = (local_supported_features[bit_idx >> 3] & (1<<(bit_idx & 7))) != 0;
        if (feature_set) continue;
        log_info("Features bit %02u is not set, removing packet types 0x%04x", bit_idx, packet_type_feature_packet_mask[i]);
        packet_types &= ~packet_type_feature_packet_mask[i];
    }
    // flip bits for "may not be used"
    packet_types ^= 0x3306;
    return packet_types;
}

uint16_t hci_usable_acl_packet_types(void){
    return hci_stack->packet_types;
}

uint8_t* hci_get_outgoing_packet_buffer(void){
    // hci packet buffer is >= acl data packet length
    return hci_stack->hci_packet_buffer;
}

uint16_t hci_max_acl_data_packet_length(void){
    return hci_stack->acl_data_packet_length;
}

int hci_non_flushable_packet_boundary_flag_supported(void){
    // No. 54, byte 6, bit 6
    return (hci_stack->local_supported_features[6] & (1 << 6)) != 0;
}

int hci_ssp_supported(void){
    // No. 51, byte 6, bit 3
    return (hci_stack->local_supported_features[6] & (1 << 3)) != 0;
}

int hci_classic_supported(void){
    // No. 37, byte 4, bit 5, = No BR/EDR Support
    return (hci_stack->local_supported_features[4] & (1 << 5)) == 0;
}

int hci_le_supported(void){
#ifdef HAVE_BLE
    // No. 37, byte 4, bit 6 = LE Supported (Controller)
    return (hci_stack->local_supported_features[4] & (1 << 6)) != 0;
#else
    return 0;
#endif
}

// get addr type and address used in advertisement packets
void hci_le_advertisement_address(uint8_t * addr_type, bd_addr_t * addr){
    *addr_type = hci_stack->adv_addr_type;
    if (hci_stack->adv_addr_type){
        memcpy(addr, hci_stack->adv_address, 6);
    } else {
        memcpy(addr, hci_stack->local_bd_addr, 6);
    }
}

#ifdef HAVE_BLE
void le_handle_advertisement_report(uint8_t *packet, int size){
    int offset = 3;
    int num_reports = packet[offset];
    offset += 1;

    int i;
    log_info("HCI: handle adv report with num reports: %d", num_reports);
    uint8_t event[12 + LE_ADVERTISING_DATA_SIZE]; // use upper bound to avoid var size automatic var
    for (i=0; i<num_reports;i++){
        uint8_t data_length = packet[offset + 8];
        uint8_t event_size = 10 + data_length;
        int pos = 0;
        event[pos++] = GAP_LE_ADVERTISING_REPORT;
        event[pos++] = event_size;
        memcpy(&event[pos], &packet[offset], 1+1+6); // event type + address type + address
        offset += 8;
        pos += 8;
        event[pos++] = packet[offset + 1 + data_length]; // rssi
        event[pos++] = packet[offset++]; //data_length;
        memcpy(&event[pos], &packet[offset], data_length);
        pos += data_length;
        offset += data_length + 1; // rssi
        hci_dump_packet( HCI_EVENT_PACKET, 0, event, pos);
        hci_stack->packet_handler(HCI_EVENT_PACKET, event, pos);
    }
}
#endif

static void hci_initializing_event_handler(uint8_t * packet, uint16_t size){
    uint8_t command_completed = 0;
    if ((hci_stack->substate % 2) == 0) return;
    // odd: waiting for event
    if (packet[0] == HCI_EVENT_COMMAND_COMPLETE){
        uint16_t opcode = READ_BT_16(packet,3);
        if (opcode == hci_stack->last_cmd_opcode){
            command_completed = 1;
            log_info("Command complete for expected opcode %04x -> new substate %u", opcode, hci_stack->substate >> 1);
        } else {
            log_info("Command complete for opcode %04x, expected %04x", opcode, hci_stack->last_cmd_opcode);
        }
    }
    if (packet[0] == HCI_EVENT_COMMAND_STATUS){
        uint8_t  status = packet[2];
        uint16_t opcode = READ_BT_16(packet,4);
        if (opcode == hci_stack->last_cmd_opcode){
            if (status){
                command_completed = 1;
                log_error("Command status error 0x%02x for expected opcode %04x -> new substate %u", status, opcode, hci_stack->substate >> 1);
            } else {
                log_info("Command status OK for expected opcode %04x, waiting for command complete", opcode);
            }
        } else {
            log_info("Command status for opcode %04x, expected %04x", opcode, hci_stack->last_cmd_opcode);
        }
    }

    if (!command_completed) return;

    switch(hci_stack->substate >> 1){
        default:
            hci_stack->substate++;
            break;
    }
}

static void hci_initializing_state_machine(){
    if (hci_stack->substate % 2) {
        // odd: waiting for command completion
        return;
    }
    // log_info("hci_init: substate %u", hci_stack->substate >> 1);
    switch (hci_stack->substate >> 1){
        case 0: // RESET
            hci_state_reset();

            hci_send_cmd(&hci_reset);
            if (hci_stack->config == NULL || ((hci_uart_config_t *)hci_stack->config)->baudrate_main == 0){
                // skip baud change
                hci_stack->substate = 2 << 1;
            }
            break;
        case 1: // SEND BAUD CHANGE
            hci_stack->control->baudrate_cmd(hci_stack->config, ((hci_uart_config_t *)hci_stack->config)->baudrate_main, hci_stack->hci_packet_buffer);
            hci_stack->last_cmd_opcode = READ_BT_16(hci_stack->hci_packet_buffer, 0);
            hci_send_cmd_packet(hci_stack->hci_packet_buffer, 3 + hci_stack->hci_packet_buffer[2]);
            break;
        case 2: // LOCAL BAUD CHANGE
            log_info("Local baud rate change");
            hci_stack->hci_transport->set_baudrate(((hci_uart_config_t *)hci_stack->config)->baudrate_main);
            hci_stack->substate += 2;
            // break missing here for fall through

        case 3: // SET BD ADDR
            if ( hci_stack->custom_bd_addr_set && hci_stack->control && hci_stack->control->set_bd_addr_cmd){
                log_info("Set Public BD ADDR to %s", bd_addr_to_str(hci_stack->custom_bd_addr));
                hci_stack->control->set_bd_addr_cmd(hci_stack->config, hci_stack->custom_bd_addr, hci_stack->hci_packet_buffer);
                hci_stack->last_cmd_opcode = READ_BT_16(hci_stack->hci_packet_buffer, 0);
                hci_send_cmd_packet(hci_stack->hci_packet_buffer, 3 + hci_stack->hci_packet_buffer[2]);
                break;
            }
            hci_stack->substate += 2;
            // break missing here for fall through

        case 4:
            log_info("Custom init");
            // Custom initialization
            if (hci_stack->control && hci_stack->control->next_cmd){
                int valid_cmd = (*hci_stack->control->next_cmd)(hci_stack->config, hci_stack->hci_packet_buffer);
                if (valid_cmd){
                    int size = 3 + hci_stack->hci_packet_buffer[2];
                    hci_stack->last_cmd_opcode = READ_BT_16(hci_stack->hci_packet_buffer, 0);
                    hci_dump_packet(HCI_COMMAND_DATA_PACKET, 0, hci_stack->hci_packet_buffer, size);
                    hci_stack->hci_transport->send_packet(HCI_COMMAND_DATA_PACKET, hci_stack->hci_packet_buffer, size);
                    hci_stack->substate = 3 << 1; // more init commands
                    break;
                }
                log_info("hci_run: init script done");
            }
            // otherwise continue
            hci_send_cmd(&hci_read_bd_addr);
            break;
        case 5:
            hci_send_cmd(&hci_read_buffer_size);
            break;
        case 6:
            hci_send_cmd(&hci_read_local_supported_features);
            break;
        case 7:
            if (hci_le_supported()){
                hci_send_cmd(&hci_set_event_mask,0xffffffff, 0x3FFFFFFF);
            } else {
                // Kensington Bluetooth 2.1 USB Dongle (CSR Chipset) returns an error for 0xffff...
                hci_send_cmd(&hci_set_event_mask,0xffffffff, 0x1FFFFFFF);
            }

            // skip Classic init commands for LE only chipsets
            if (!hci_classic_supported()){
                if (hci_le_supported()){
                    hci_stack->substate = 12 << 1;    // skip all classic command
                } else {
                    log_error("Neither BR/EDR nor LE supported");
                    hci_stack->substate = 15 << 1;    // skip all
                }
            }
            break;
        case 8:
            if (hci_ssp_supported()){
                hci_send_cmd(&hci_write_simple_pairing_mode, hci_stack->ssp_enable);
                break;
            }
            hci_stack->substate += 2;
            // break missing here for fall through

        case 9:
            // ca. 15 sec
            hci_send_cmd(&hci_write_page_timeout, 0x6000);
            break;
        case 10:
            hci_send_cmd(&hci_write_class_of_device, hci_stack->class_of_device);
            break;
        case 11:
            if (hci_stack->local_name){
                hci_send_cmd(&hci_write_local_name, hci_stack->local_name);
            } else {
                char hostname[30];
#ifdef EMBEDDED
                // BTstack-11:22:33:44:55:66
                strcpy(hostname, "BTstack ");
                strcat(hostname, bd_addr_to_str(hci_stack->local_bd_addr));
                log_info("---> Name %s", hostname);
#else
                // hostname for POSIX systems
                gethostname(hostname, 30);
                hostname[29] = '\0';
#endif
                hci_send_cmd(&hci_write_local_name, hostname);
            }
            break;
        case 12:
            hci_send_cmd(&hci_write_scan_enable, (hci_stack->connectable << 1) | hci_stack->discoverable); // page scan
            if (!hci_le_supported()){
                // SKIP LE init for Classic only configuration
                hci_stack->substate = 15 << 1;
            }
            break;

#ifdef HAVE_BLE
        // LE INIT
        case 13:
            hci_send_cmd(&hci_le_read_buffer_size);
            break;
        case 14:
            // LE Supported Host = 1, Simultaneous Host = 0
            hci_send_cmd(&hci_write_le_host_supported, 1, 0);
            break;
        case 15:
            // LE Scan Parameters: active scanning, 300 ms interval, 30 ms window, public address, accept all advs
            hci_send_cmd(&hci_le_set_scan_parameters, 1, 0x1e0, 0x30, 0, 0);
            break;
#endif

        // DONE
        case 16:
            // done.
            hci_stack->state = HCI_STATE_WORKING;
            hci_emit_state();
            break;
        default:
            break;
    }
    hci_stack->substate++;
}

// avoid huge local variables
#ifndef EMBEDDED
static device_name_t device_name;
#endif
static void event_handler(uint8_t *packet, int size){

    uint16_t event_length = packet[1];

    // assert packet is complete
    if (size != event_length + 2){
        log_error("hci.c: event_handler called with event packet of wrong size %u, expected %u => dropping packet", size, event_length + 2);
        return;
    }

    bd_addr_t addr;
    bd_addr_type_t addr_type;
    uint8_t link_type;
    hci_con_handle_t handle;
    hci_connection_t * conn;
    int i;

    // log_info("HCI:EVENT:%02x", packet[0]);

    switch (packet[0]) {

        case HCI_EVENT_COMMAND_COMPLETE:
            // get num cmd packets
            // log_info("HCI_EVENT_COMMAND_COMPLETE cmds old %u - new %u", hci_stack->num_cmd_packets, packet[2]);
            hci_stack->num_cmd_packets = packet[2];

            if (COMMAND_COMPLETE_EVENT(packet, hci_read_buffer_size)){
                // from offset 5
                // status
                // "The HC_ACL_Data_Packet_Length return parameter will be used to determine the size of the L2CAP segments contained in ACL Data Packets"
                hci_stack->acl_data_packet_length = READ_BT_16(packet, 6);
                hci_stack->sco_data_packet_length = packet[8];
                hci_stack->acl_packets_total_num  = packet[9];
                hci_stack->sco_packets_total_num  = packet[10];

                if (hci_stack->state == HCI_STATE_INITIALIZING){
                    // determine usable ACL payload size
                    if (HCI_ACL_PAYLOAD_SIZE < hci_stack->acl_data_packet_length){
                        hci_stack->acl_data_packet_length = HCI_ACL_PAYLOAD_SIZE;
                    }
                    log_info("hci_read_buffer_size: used size %u, count %u",
                             hci_stack->acl_data_packet_length, hci_stack->acl_packets_total_num);
                }
            }
#ifdef HAVE_BLE
            if (COMMAND_COMPLETE_EVENT(packet, hci_le_read_buffer_size)){
                hci_stack->le_data_packets_length = READ_BT_16(packet, 6);
                hci_stack->le_acl_packets_total_num  = packet[8];
                    // determine usable ACL payload size
                    if (HCI_ACL_PAYLOAD_SIZE < hci_stack->le_data_packets_length){
                        hci_stack->le_data_packets_length = HCI_ACL_PAYLOAD_SIZE;
                    }
                log_info("hci_le_read_buffer_size: size %u, count %u", hci_stack->le_data_packets_length, hci_stack->le_acl_packets_total_num);
            }
#endif
            // Dump local address
            if (COMMAND_COMPLETE_EVENT(packet, hci_read_bd_addr)) {
                bt_flip_addr(hci_stack->local_bd_addr, &packet[OFFSET_OF_DATA_IN_COMMAND_COMPLETE + 1]);
                log_info("Local Address, Status: 0x%02x: Addr: %s",
                    packet[OFFSET_OF_DATA_IN_COMMAND_COMPLETE], bd_addr_to_str(hci_stack->local_bd_addr));
            }
            if (COMMAND_COMPLETE_EVENT(packet, hci_write_scan_enable)){
                hci_emit_discoverable_enabled(hci_stack->discoverable);
            }
            // Note: HCI init checks
            if (COMMAND_COMPLETE_EVENT(packet, hci_read_local_supported_features)){
                memcpy(hci_stack->local_supported_features, &packet[OFFSET_OF_DATA_IN_COMMAND_COMPLETE+1], 8);
                log_info("Local Supported Features: 0x%02x%02x%02x%02x%02x%02x%02x%02x",
                    hci_stack->local_supported_features[0], hci_stack->local_supported_features[1],
                    hci_stack->local_supported_features[2], hci_stack->local_supported_features[3],
                    hci_stack->local_supported_features[4], hci_stack->local_supported_features[5],
                    hci_stack->local_supported_features[6], hci_stack->local_supported_features[7]);

                // determine usable ACL packet types based on host buffer size and supported features
                hci_stack->packet_types = hci_acl_packet_types_for_buffer_size_and_local_features(HCI_ACL_PAYLOAD_SIZE, &hci_stack->local_supported_features[0]);
                log_info("packet types %04x", hci_stack->packet_types);

                // Classic/LE
                log_info("BR/EDR support %u, LE support %u", hci_classic_supported(), hci_le_supported());
            }
            break;

        case HCI_EVENT_COMMAND_STATUS:
            // get num cmd packets
            // log_info("HCI_EVENT_COMMAND_STATUS cmds - old %u - new %u", hci_stack->num_cmd_packets, packet[3]);
            hci_stack->num_cmd_packets = packet[3];
            break;

        case HCI_EVENT_NUMBER_OF_COMPLETED_PACKETS:{
            int offset = 3;
            for (i=0; i<packet[2];i++){
                handle = READ_BT_16(packet, offset);
                offset += 2;
                uint16_t num_packets = READ_BT_16(packet, offset);
                offset += 2;

                conn = hci_connection_for_handle(handle);
                if (!conn){
                    log_error("hci_number_completed_packet lists unused con handle %u", handle);
                    continue;
                }

                if (conn->address_type == BD_ADDR_TYPE_SCO){
                    if (conn->num_sco_packets_sent >= num_packets){
                        conn->num_sco_packets_sent -= num_packets;
                    } else {
                        log_error("hci_number_completed_packets, more sco slots freed then sent.");
                        conn->num_sco_packets_sent = 0;
                    }

                } else {
                    if (conn->num_acl_packets_sent >= num_packets){
                        conn->num_acl_packets_sent -= num_packets;
                    } else {
                        log_error("hci_number_completed_packets, more acl slots freed then sent.");
                        conn->num_acl_packets_sent = 0;
                    }
                }
                // log_info("hci_number_completed_packet %u processed for handle %u, outstanding %u", num_packets, handle, conn->num_acl_packets_sent);
            }
            break;
        }
        case HCI_EVENT_CONNECTION_REQUEST:
            bt_flip_addr(addr, &packet[2]);
            // TODO: eval COD 8-10
            link_type = packet[11];
            log_info("Connection_incoming: %s, type %u", bd_addr_to_str(addr), link_type);
            addr_type = link_type == 1 ? BD_ADDR_TYPE_CLASSIC : BD_ADDR_TYPE_SCO;
            conn = hci_connection_for_bd_addr_and_type(&addr, BD_ADDR_TYPE_CLASSIC);
            if (!conn) {
                conn = create_connection_for_bd_addr_and_type(addr, BD_ADDR_TYPE_CLASSIC);
            }
            if (!conn) {
                // CONNECTION REJECTED DUE TO LIMITED RESOURCES (0X0D)
                hci_stack->decline_reason = 0x0d;
                BD_ADDR_COPY(hci_stack->decline_addr, addr);
                break;
            }
            conn->state = RECEIVED_CONNECTION_REQUEST;
            hci_run();
            break;

        case HCI_EVENT_CONNECTION_COMPLETE:
            // Connection management
            bt_flip_addr(addr, &packet[5]);
            log_info("Connection_complete (status=%u) %s", packet[2], bd_addr_to_str(addr));
            addr_type = BD_ADDR_TYPE_CLASSIC;
            conn = hci_connection_for_bd_addr_and_type(&addr, addr_type);
            if (conn) {
                if (!packet[2]){
                    conn->state = OPEN;
                    conn->con_handle = READ_BT_16(packet, 3);
                    conn->bonding_flags |= BONDING_REQUEST_REMOTE_FEATURES;

                    // restart timer
                    run_loop_set_timer(&conn->timeout, HCI_CONNECTION_TIMEOUT_MS);
                    run_loop_add_timer(&conn->timeout);

                    log_info("New connection: handle %u, %s", conn->con_handle, bd_addr_to_str(conn->address));

                    hci_emit_nr_connections_changed();
                } else {
                    int notify_dedicated_bonding_failed = conn->bonding_flags & BONDING_DEDICATED;
                    uint8_t status = packet[2];
                    bd_addr_t bd_address;
                    memcpy(&bd_address, conn->address, 6);

                    // connection failed, remove entry
                    linked_list_remove(&hci_stack->connections, (linked_item_t *) conn);
                    btstack_memory_hci_connection_free( conn );

                    // notify client if dedicated bonding
                    if (notify_dedicated_bonding_failed){
                        log_info("hci notify_dedicated_bonding_failed");
                        hci_emit_dedicated_bonding_result(bd_address, status);
                    }

                    // if authentication error, also delete link key
                    if (packet[2] == 0x05) {
                        hci_drop_link_key_for_bd_addr(&addr);
                    }
                }
            }
            break;

        case HCI_EVENT_SYNCHRONOUS_CONNECTION_COMPLETE:
            bt_flip_addr(addr, &packet[5]);
            log_info("Synchronous Connection Complete (status=%u) %s", packet[2], bd_addr_to_str(addr));
            if (!packet[2]){
                // connection failed
                break;
            }
            conn = hci_connection_for_bd_addr_and_type(&addr, BD_ADDR_TYPE_SCO);
            if (!conn) {
                conn = create_connection_for_bd_addr_and_type(addr, BD_ADDR_TYPE_SCO);
            }
            if (!conn) {
                break;
            }
            break;

        case HCI_EVENT_READ_REMOTE_SUPPORTED_FEATURES_COMPLETE:
            handle = READ_BT_16(packet, 3);
            conn = hci_connection_for_handle(handle);
            if (!conn) break;
            if (!packet[2]){
                uint8_t * features = &packet[5];
                if (features[6] & (1 << 3)){
                    conn->bonding_flags |= BONDING_REMOTE_SUPPORTS_SSP;
                }
            }
            conn->bonding_flags |= BONDING_RECEIVED_REMOTE_FEATURES;
            log_info("HCI_EVENT_READ_REMOTE_SUPPORTED_FEATURES_COMPLETE, bonding flags %x", conn->bonding_flags);
            if (conn->bonding_flags & BONDING_DEDICATED){
                conn->bonding_flags |= BONDING_SEND_AUTHENTICATE_REQUEST;
            }
            break;

        case HCI_EVENT_LINK_KEY_REQUEST:
            log_info("HCI_EVENT_LINK_KEY_REQUEST");
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], RECV_LINK_KEY_REQUEST);
            // non-bondable mode: link key negative reply will be sent by HANDLE_LINK_KEY_REQUEST
            if (hci_stack->bondable && !hci_stack->remote_device_db) break;
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], HANDLE_LINK_KEY_REQUEST);
            hci_run();
            // request handled by hci_run() as HANDLE_LINK_KEY_REQUEST gets set
            return;

        case HCI_EVENT_LINK_KEY_NOTIFICATION: {
            bt_flip_addr(addr, &packet[2]);
            conn = hci_connection_for_bd_addr_and_type(&addr, BD_ADDR_TYPE_CLASSIC);
            if (!conn) break;
            conn->authentication_flags |= RECV_LINK_KEY_NOTIFICATION;
            link_key_type_t link_key_type = (link_key_type_t)packet[24];
            // Change Connection Encryption keeps link key type
            if (link_key_type != CHANGED_COMBINATION_KEY){
                conn->link_key_type = link_key_type;
            }
            if (!hci_stack->remote_device_db) break;
            hci_stack->remote_device_db->put_link_key(&addr, (link_key_t *) &packet[8], conn->link_key_type);
            // still forward event to allow dismiss of pairing dialog
            break;
        }

        case HCI_EVENT_PIN_CODE_REQUEST:
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], LEGACY_PAIRING_ACTIVE);
            // non-bondable mode: pin code negative reply will be sent
            if (!hci_stack->bondable){
                hci_add_connection_flags_for_flipped_bd_addr(&packet[2], DENY_PIN_CODE_REQUEST);
                hci_run();
                return;
            }
            // PIN CODE REQUEST means the link key request didn't succee -> delete stored link key
            if (!hci_stack->remote_device_db) break;
            bt_flip_addr(addr, &packet[2]);
            hci_stack->remote_device_db->delete_link_key(&addr);
            break;

        case HCI_EVENT_IO_CAPABILITY_REQUEST:
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], RECV_IO_CAPABILITIES_REQUEST);
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], SEND_IO_CAPABILITIES_REPLY);
            break;

        case HCI_EVENT_USER_CONFIRMATION_REQUEST:
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], SSP_PAIRING_ACTIVE);
            if (!hci_stack->ssp_auto_accept) break;
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], SEND_USER_CONFIRM_REPLY);
            break;

        case HCI_EVENT_USER_PASSKEY_REQUEST:
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], SSP_PAIRING_ACTIVE);
            if (!hci_stack->ssp_auto_accept) break;
            hci_add_connection_flags_for_flipped_bd_addr(&packet[2], SEND_USER_PASSKEY_REPLY);
            break;

        case HCI_EVENT_ENCRYPTION_CHANGE:
            handle = READ_BT_16(packet, 3);
            conn = hci_connection_for_handle(handle);
            if (!conn) break;
            if (packet[2] == 0) {
                if (packet[5]){
                    conn->authentication_flags |= CONNECTION_ENCRYPTED;
                } else {
                    conn->authentication_flags &= ~CONNECTION_ENCRYPTED;
                }
            }
            hci_emit_security_level(handle, gap_security_level_for_connection(conn));
            break;

        case HCI_EVENT_AUTHENTICATION_COMPLETE_EVENT:
            handle = READ_BT_16(packet, 3);
            conn = hci_connection_for_handle(handle);
            if (!conn) break;

            // dedicated bonding: send result and disconnect
            if (conn->bonding_flags & BONDING_DEDICATED){
                conn->bonding_flags &= ~BONDING_DEDICATED;
                conn->bonding_flags |= BONDING_DISCONNECT_DEDICATED_DONE;
                conn->bonding_status = packet[2];
                break;
            }

            if (packet[2] == 0 && gap_security_level_for_link_key_type(conn->link_key_type) >= conn->requested_security_level){
                // link key sufficient for requested security
                conn->bonding_flags |= BONDING_SEND_ENCRYPTION_REQUEST;
                break;
            }
            // not enough
            hci_emit_security_level(handle, gap_security_level_for_connection(conn));
            break;

#ifndef EMBEDDED
        case HCI_EVENT_REMOTE_NAME_REQUEST_COMPLETE:
            if (!hci_stack->remote_device_db) break;
            if (packet[2]) break; // status not ok
            bt_flip_addr(addr, &packet[3]);
            // fix for invalid remote names - terminate on 0xff
            for (i=0; i<248;i++){
                if (packet[9+i] == 0xff){
                    packet[9+i] = 0;
                    break;
                }
            }
            memset(&device_name, 0, sizeof(device_name_t));
            strncpy((char*) device_name, (char*) &packet[9], 248);
            hci_stack->remote_device_db->put_name(&addr, &device_name);
            break;

        case HCI_EVENT_INQUIRY_RESULT:
        case HCI_EVENT_INQUIRY_RESULT_WITH_RSSI:{
            if (!hci_stack->remote_device_db) break;
            // first send inq result packet
            hci_stack->packet_handler(HCI_EVENT_PACKET, packet, size);
            // then send cached remote names
            int offset = 3;
            for (i=0; i<packet[2];i++){
                bt_flip_addr(addr, &packet[offset]);
                offset += 14; // 6 + 1 + 1 + 1 + 3 + 2;
                if (hci_stack->remote_device_db->get_name(&addr, &device_name)){
                    hci_emit_remote_name_cached(&addr, &device_name);
                }
            }
            return;
        }
#endif

        // HCI_EVENT_DISCONNECTION_COMPLETE
        // has been split, to first notify stack before shutting connection down
        // see end of function, too.
        case HCI_EVENT_DISCONNECTION_COMPLETE:
            if (packet[2]) break;   // status != 0
            handle = READ_BT_16(packet, 3);
            hci_connection_t * conn = hci_connection_for_handle(handle);
            if (!conn) break;       // no conn struct anymore
            conn->state = RECEIVED_DISCONNECTION_COMPLETE;
            break;

        case HCI_EVENT_HARDWARE_ERROR:
            if(hci_stack->control && hci_stack->control->hw_error){
                (*hci_stack->control->hw_error)();
            } else {
                // if no special requests, just reboot stack
                hci_power_control_off();
                hci_power_control_on();
            }
            break;

        case DAEMON_EVENT_HCI_PACKET_SENT:
            // release packet buffer only for asynchronous transport and if there are not further fragements
            if (hci_transport_synchronous()) {
                log_error("Synchronous HCI Transport shouldn't send DAEMON_EVENT_HCI_PACKET_SENT");
                return; // instead of break: to avoid re-entering hci_run()
            }
            if (hci_stack->acl_fragmentation_total_size) break;
            hci_release_packet_buffer();
            break;

#ifdef HAVE_BLE
        case HCI_EVENT_LE_META:
            switch (packet[2]){
                case HCI_SUBEVENT_LE_ADVERTISING_REPORT:
                    log_info("advertising report received");
                    if (hci_stack->le_scanning_state != LE_SCANNING) break;
                    le_handle_advertisement_report(packet, size);
                    break;
                case HCI_SUBEVENT_LE_CONNECTION_COMPLETE:
                    // Connection management
                    bt_flip_addr(addr, &packet[8]);
                    addr_type = (bd_addr_type_t)packet[7];
                    log_info("LE Connection_complete (status=%u) type %u, %s", packet[3], addr_type, bd_addr_to_str(addr));
                    // LE connections are auto-accepted, so just create a connection if there isn't one already
                    conn = hci_connection_for_bd_addr_and_type(&addr, addr_type);
                    if (packet[3]){
                        if (conn){
                            // outgoing connection failed, remove entry
                            linked_list_remove(&hci_stack->connections, (linked_item_t *) conn);
                            btstack_memory_hci_connection_free( conn );
                        }
                        // if authentication error, also delete link key
                        if (packet[3] == 0x05) {
                            hci_drop_link_key_for_bd_addr(&addr);
                        }
                        break;
                    }
                    if (!conn){
                        conn = create_connection_for_bd_addr_and_type(addr, addr_type);
                    }
                    if (!conn){
                        // no memory
                        break;
                    }

                    conn->state = OPEN;
                    conn->con_handle = READ_BT_16(packet, 4);

                    // TODO: store - role, peer address type, conn_interval, conn_latency, supervision timeout, master clock

                    // restart timer
                    // run_loop_set_timer(&conn->timeout, HCI_CONNECTION_TIMEOUT_MS);
                    // run_loop_add_timer(&conn->timeout);

                    log_info("New connection: handle %u, %s", conn->con_handle, bd_addr_to_str(conn->address));

                    hci_emit_nr_connections_changed();
                    break;

            // log_info("LE buffer size: %u, count %u", READ_BT_16(packet,6), packet[8]);

                default:
                    break;
            }
            break;
#endif
        default:
            break;
    }

    // handle BT initialization
    if (hci_stack->state == HCI_STATE_INITIALIZING){
        hci_initializing_event_handler(packet, size);
    }

    // help with BT sleep
    if (hci_stack->state == HCI_STATE_FALLING_ASLEEP
        && hci_stack->substate == 1
        && COMMAND_COMPLETE_EVENT(packet, hci_write_scan_enable)){
        hci_stack->substate++;
    }

    // notify upper stack
    hci_stack->packet_handler(HCI_EVENT_PACKET, packet, size);

    // moved here to give upper stack a chance to close down everything with hci_connection_t intact
    if (packet[0] == HCI_EVENT_DISCONNECTION_COMPLETE){
        if (!packet[2]){
            handle = READ_BT_16(packet, 3);
            hci_connection_t * conn = hci_connection_for_handle(handle);
            if (conn) {
                uint8_t status = conn->bonding_status;
                uint16_t flags = conn->bonding_flags;
                bd_addr_t bd_address;
                memcpy(&bd_address, conn->address, 6);
                hci_shutdown_connection(conn);
                // connection struct is gone, don't access anymore
                if (flags & BONDING_EMIT_COMPLETE_ON_DISCONNECT){
                    hci_emit_dedicated_bonding_result(bd_address, status);
                }
            }
        }
    }

	// execute main loop
	hci_run();
}

static void sco_handler(uint8_t * packet, uint16_t size){
    // not handled yet
}

static void packet_handler(uint8_t packet_type, uint8_t *packet, uint16_t size){
    hci_dump_packet(packet_type, 1, packet, size);
    switch (packet_type) {
        case HCI_EVENT_PACKET:
            event_handler(packet, size);
            break;
        case HCI_ACL_DATA_PACKET:
            acl_handler(packet, size);
            break;
        case HCI_SCO_DATA_PACKET:
            sco_handler(packet, size);
        default:
            break;
    }
}

/** Register HCI packet handlers */
void hci_register_packet_handler(void (*handler)(uint8_t packet_type, uint8_t *packet, uint16_t size)){
    hci_stack->packet_handler = handler;
}

static void hci_state_reset(){
    // no connections yet
    hci_stack->connections = NULL;

    // keep discoverable/connectable as this has been requested by the client(s)
    // hci_stack->discoverable = 0;
    // hci_stack->connectable = 0;
    // hci_stack->bondable = 1;

    // buffer is free
    hci_stack->hci_packet_buffer_reserved = 0;

    // no pending cmds
    hci_stack->decline_reason = 0;
    hci_stack->new_scan_enable_value = 0xff;

    // LE
    hci_stack->adv_addr_type = 0;
    memset(hci_stack->adv_address, 0, 6);
    hci_stack->le_scanning_state = LE_SCAN_IDLE;
    hci_stack->le_scan_type = 0xff;
    hci_stack->le_connection_parameter_range.le_conn_interval_min = 0x0006;
    hci_stack->le_connection_parameter_range.le_conn_interval_max = 0x0C80;
    hci_stack->le_connection_parameter_range.le_conn_latency_min = 0x0000;
    hci_stack->le_connection_parameter_range.le_conn_latency_max = 0x03E8;
    hci_stack->le_connection_parameter_range.le_supervision_timeout_min = 0x000A;
    hci_stack->le_connection_parameter_range.le_supervision_timeout_max = 0x0C80;
}

void hci_init(hci_transport_t *transport, void *config, bt_control_t *control, remote_device_db_t const* remote_device_db){

#ifdef HAVE_MALLOC
    if (!hci_stack) {
        hci_stack = (hci_stack_t*) malloc(sizeof(hci_stack_t));
    }
#else
    hci_stack = &hci_stack_static;
#endif
    memset(hci_stack, 0, sizeof(hci_stack_t));

    // reference to use transport layer implementation
    hci_stack->hci_transport = transport;

    // references to used control implementation
    hci_stack->control = control;

    // reference to used config
    hci_stack->config = config;

    // higher level handler
    hci_stack->packet_handler = dummy_handler;

    // store and open remote device db
    hci_stack->remote_device_db = remote_device_db;
    if (hci_stack->remote_device_db) {
        hci_stack->remote_device_db->open();
    }

    // max acl payload size defined in config.h
    hci_stack->acl_data_packet_length = HCI_ACL_PAYLOAD_SIZE;

    // register packet handlers with transport
    transport->register_packet_handler(&packet_handler);

    hci_stack->state = HCI_STATE_OFF;

    // class of device
    hci_stack->class_of_device = 0x007a020c; // Smartphone

    // bondable by default
    hci_stack->bondable = 1;

    // Secure Simple Pairing default: enable, no I/O capabilities, general bonding, mitm not required, auto accept
    hci_stack->ssp_enable = 1;
    hci_stack->ssp_io_capability = SSP_IO_CAPABILITY_NO_INPUT_NO_OUTPUT;
    hci_stack->ssp_authentication_requirement = SSP_IO_AUTHREQ_MITM_PROTECTION_NOT_REQUIRED_GENERAL_BONDING;
    hci_stack->ssp_auto_accept = 1;

    hci_state_reset();
}

void hci_close(){
    // close remote device db
    if (hci_stack->remote_device_db) {
        hci_stack->remote_device_db->close();
    }
    while (hci_stack->connections) {
        // cancel all l2cap connections
        hci_emit_disconnection_complete(((hci_connection_t *) hci_stack->connections)->con_handle, 0x16); // terminated by local host
        hci_shutdown_connection((hci_connection_t *) hci_stack->connections);
    }
    hci_power_control(HCI_POWER_OFF);

#ifdef HAVE_MALLOC
    free(hci_stack);
#endif
    hci_stack = NULL;
}

void hci_set_class_of_device(uint32_t class_of_device){
    hci_stack->class_of_device = class_of_device;
}

// Set Public BD ADDR - passed on to Bluetooth chipset if supported in bt_control_h
void hci_set_bd_addr(bd_addr_t addr){
    memcpy(hci_stack->custom_bd_addr, addr, 6);
    hci_stack->custom_bd_addr_set = 1;
}

void hci_disable_l2cap_timeout_check(){
    disable_l2cap_timeouts = 1;
}
// State-Module-Driver overview
// state                    module  low-level
// HCI_STATE_OFF             off      close
// HCI_STATE_INITIALIZING,   on       open
// HCI_STATE_WORKING,        on       open
// HCI_STATE_HALTING,        on       open
// HCI_STATE_SLEEPING,    off/sleep   close
// HCI_STATE_FALLING_ASLEEP  on       open

static int hci_power_control_on(void){

    // power on
    int err = 0;
    if (hci_stack->control && hci_stack->control->on){
        err = (*hci_stack->control->on)(hci_stack->config);
    }
    if (err){
        log_error( "POWER_ON failed");
        hci_emit_hci_open_failed();
        return err;
    }

    // open low-level device
    err = hci_stack->hci_transport->open(hci_stack->config);
    if (err){
        log_error( "HCI_INIT failed, turning Bluetooth off again");
        if (hci_stack->control && hci_stack->control->off){
            (*hci_stack->control->off)(hci_stack->config);
        }
        hci_emit_hci_open_failed();
        return err;
    }
    return 0;
}

static void hci_power_control_off(void){

    log_info("hci_power_control_off");

    // close low-level device
    hci_stack->hci_transport->close(hci_stack->config);

    log_info("hci_power_control_off - hci_transport closed");

    // power off
    if (hci_stack->control && hci_stack->control->off){
        (*hci_stack->control->off)(hci_stack->config);
    }

    log_info("hci_power_control_off - control closed");

    hci_stack->state = HCI_STATE_OFF;
}

static void hci_power_control_sleep(void){

    log_info("hci_power_control_sleep");

#if 0
    // don't close serial port during sleep

    // close low-level device
    hci_stack->hci_transport->close(hci_stack->config);
#endif

    // sleep mode
    if (hci_stack->control && hci_stack->control->sleep){
        (*hci_stack->control->sleep)(hci_stack->config);
    }

    hci_stack->state = HCI_STATE_SLEEPING;
}

static int hci_power_control_wake(void){

    log_info("hci_power_control_wake");

    // wake on
    if (hci_stack->control && hci_stack->control->wake){
        (*hci_stack->control->wake)(hci_stack->config);
    }

#if 0
    // open low-level device
    int err = hci_stack->hci_transport->open(hci_stack->config);
    if (err){
        log_error( "HCI_INIT failed, turning Bluetooth off again");
        if (hci_stack->control && hci_stack->control->off){
            (*hci_stack->control->off)(hci_stack->config);
        }
        hci_emit_hci_open_failed();
        return err;
    }
#endif

    return 0;
}

static void hci_power_transition_to_initializing(void){
    // set up state machine
    hci_stack->num_cmd_packets = 1; // assume that one cmd can be sent
    hci_stack->hci_packet_buffer_reserved = 0;
    hci_stack->state = HCI_STATE_INITIALIZING;
    hci_stack->substate = 0;
}

int hci_power_control(HCI_POWER_MODE power_mode){

    log_info("hci_power_control: %u, current mode %u", power_mode, hci_stack->state);

    int err = 0;
    switch (hci_stack->state){

        case HCI_STATE_OFF:
            switch (power_mode){
                case HCI_POWER_ON:
                    err = hci_power_control_on();
                    if (err) {
                        log_error("hci_power_control_on() error %u", err);
                        return err;
                    }
                    hci_power_transition_to_initializing();
                    break;
                case HCI_POWER_OFF:
                    // do nothing
                    break;
                case HCI_POWER_SLEEP:
                    // do nothing (with SLEEP == OFF)
                    break;
            }
            break;

        case HCI_STATE_INITIALIZING:
            switch (power_mode){
                case HCI_POWER_ON:
                    // do nothing
                    break;
                case HCI_POWER_OFF:
                    // no connections yet, just turn it off
                    hci_power_control_off();
                    break;
                case HCI_POWER_SLEEP:
                    // no connections yet, just turn it off
                    hci_power_control_sleep();
                    break;
            }
            break;

        case HCI_STATE_WORKING:
            switch (power_mode){
                case HCI_POWER_ON:
                    // do nothing
                    break;
                case HCI_POWER_OFF:
                    // see hci_run
                    hci_stack->state = HCI_STATE_HALTING;
                    break;
                case HCI_POWER_SLEEP:
                    // see hci_run
                    hci_stack->state = HCI_STATE_FALLING_ASLEEP;
                    hci_stack->substate = 0;
                    break;
            }
            break;

        case HCI_STATE_HALTING:
            switch (power_mode){
                case HCI_POWER_ON:
                    hci_power_transition_to_initializing();
                    break;
                case HCI_POWER_OFF:
                    // do nothing
                    break;
                case HCI_POWER_SLEEP:
                    // see hci_run
                    hci_stack->state = HCI_STATE_FALLING_ASLEEP;
                    hci_stack->substate = 0;
                    break;
            }
            break;

        case HCI_STATE_FALLING_ASLEEP:
            switch (power_mode){
                case HCI_POWER_ON:

#if defined(USE_POWERMANAGEMENT) && defined(USE_BLUETOOL)
                    // nothing to do, if H4 supports power management
                    if (bt_control_iphone_power_management_enabled()){
                        hci_stack->state = HCI_STATE_INITIALIZING;
                        hci_stack->substate = HCI_INTIALIZING_SUBSTATE_AFTER_SLEEP;
                        break;
                    }
#endif
                    hci_power_transition_to_initializing();
                    break;
                case HCI_POWER_OFF:
                    // see hci_run
                    hci_stack->state = HCI_STATE_HALTING;
                    break;
                case HCI_POWER_SLEEP:
                    // do nothing
                    break;
            }
            break;

        case HCI_STATE_SLEEPING:
            switch (power_mode){
                case HCI_POWER_ON:

#if defined(USE_POWERMANAGEMENT) && defined(USE_BLUETOOL)
                    // nothing to do, if H4 supports power management
                    if (bt_control_iphone_power_management_enabled()){
                        hci_stack->state = HCI_STATE_INITIALIZING;
                        hci_stack->substate = HCI_INTIALIZING_SUBSTATE_AFTER_SLEEP;
                        hci_update_scan_enable();
                        break;
                    }
#endif
                    err = hci_power_control_wake();
                    if (err) return err;
                    hci_power_transition_to_initializing();
                    break;
                case HCI_POWER_OFF:
                    hci_stack->state = HCI_STATE_HALTING;
                    break;
                case HCI_POWER_SLEEP:
                    // do nothing
                    break;
            }
            break;
    }

    // create internal event
	hci_emit_state();

	// trigger next/first action
	hci_run();

    return 0;
}

static void hci_update_scan_enable(void){
    // 2 = page scan, 1 = inq scan
    hci_stack->new_scan_enable_value  = hci_stack->connectable << 1 | hci_stack->discoverable;
    hci_run();
}

void hci_discoverable_control(uint8_t enable){
    if (enable) enable = 1; // normalize argument

    if (hci_stack->discoverable == enable){
        hci_emit_discoverable_enabled(hci_stack->discoverable);
        return;
    }

    hci_stack->discoverable = enable;
    hci_update_scan_enable();
}

void hci_connectable_control(uint8_t enable){
    if (enable) enable = 1; // normalize argument

    // don't emit event
    if (hci_stack->connectable == enable) return;

    hci_stack->connectable = enable;
    hci_update_scan_enable();
}

bd_addr_t * hci_local_bd_addr(void){
    return &hci_stack->local_bd_addr;
}

void hci_run(){

    hci_connection_t * connection;
    linked_item_t * it;

    // send continuation fragments first, as they block the prepared packet buffer
    if (hci_stack->acl_fragmentation_total_size > 0) {
        hci_con_handle_t con_handle = READ_ACL_CONNECTION_HANDLE(hci_stack->hci_packet_buffer);
        if (hci_can_send_prepared_acl_packet_now(con_handle)){
            hci_connection_t *connection = hci_connection_for_handle(con_handle);
            if (connection) {
                hci_send_acl_packet_fragments(connection);
                return;
            }
            // connection gone -> discard further fragments
            hci_stack->acl_fragmentation_total_size = 0;
            hci_stack->acl_fragmentation_pos = 0;
        }
    }

    if (!hci_can_send_command_packet_now()) return;

    // global/non-connection oriented commands

    // decline incoming connections
    if (hci_stack->decline_reason){
        uint8_t reason = hci_stack->decline_reason;
        hci_stack->decline_reason = 0;
        hci_send_cmd(&hci_reject_connection_request, hci_stack->decline_addr, reason);
        return;
    }

    // send scan enable
    if (hci_stack->state == HCI_STATE_WORKING && hci_stack->new_scan_enable_value != 0xff && hci_classic_supported()){
        hci_send_cmd(&hci_write_scan_enable, hci_stack->new_scan_enable_value);
        hci_stack->new_scan_enable_value = 0xff;
        return;
    }

#ifdef HAVE_BLE
    // handle le scan
    if (hci_stack->state == HCI_STATE_WORKING){
        switch(hci_stack->le_scanning_state){
            case LE_START_SCAN:
                hci_stack->le_scanning_state = LE_SCANNING;
                hci_send_cmd(&hci_le_set_scan_enable, 1, 0);
                return;

            case LE_STOP_SCAN:
                hci_stack->le_scanning_state = LE_SCAN_IDLE;
                hci_send_cmd(&hci_le_set_scan_enable, 0, 0);
                return;
            default:
                break;
        }
        if (hci_stack->le_scan_type != 0xff){
            // defaults: active scanning, accept all advertisement packets
            int scan_type = hci_stack->le_scan_type;
            hci_stack->le_scan_type = 0xff;
            hci_send_cmd(&hci_le_set_scan_parameters, scan_type, hci_stack->le_scan_interval, hci_stack->le_scan_window, hci_stack->adv_addr_type, 0);
            return;
        }
    }
#endif

    // send pending HCI commands
    for (it = (linked_item_t *) hci_stack->connections; it ; it = it->next){
        connection = (hci_connection_t *) it;

        switch(connection->state){
            case SEND_CREATE_CONNECTION:
                switch(connection->address_type){
                    case BD_ADDR_TYPE_CLASSIC:
                        log_info("sending hci_create_connection");
                        hci_send_cmd(&hci_create_connection, connection->address, hci_usable_acl_packet_types(), 0, 0, 0, 1);
                        break;
                    default:
#ifdef HAVE_BLE
                        log_info("sending hci_le_create_connection");
                        hci_send_cmd(&hci_le_create_connection,
                                     0x0060,    // scan interval: 60 ms
                                     0x0030,    // scan interval: 30 ms
                                     0,         // don't use whitelist
                                     connection->address_type, // peer address type
                                     connection->address,      // peer bd addr
                                     hci_stack->adv_addr_type, // our addr type:
                                     0x0008,    // conn interval min
                                     0x0018,    // conn interval max
                                     0,         // conn latency
                                     0x0048,    // supervision timeout
                                     0x0001,    // min ce length
                                     0x0001     // max ce length
                                     );

                        connection->state = SENT_CREATE_CONNECTION;
#endif
                        break;
                }
                return;

            case RECEIVED_CONNECTION_REQUEST:
                log_info("sending hci_accept_connection_request");
                connection->state = ACCEPTED_CONNECTION_REQUEST;
                if (connection->address_type == BD_ADDR_TYPE_CLASSIC){
                    hci_send_cmd(&hci_accept_connection_request, connection->address, 1);
                } else {
                    // TODO: allows to customize synchronous connection parameters
                    hci_send_cmd(&hci_accept_synchronous_connection_command, connection->address, 8000, 8000, 0xFFFF, 0x0060, 0xFF, 0x003F);
                }
                return;

#ifdef HAVE_BLE
            case SEND_CANCEL_CONNECTION:
                connection->state = SENT_CANCEL_CONNECTION;
                hci_send_cmd(&hci_le_create_connection_cancel);
                return;
#endif
            case SEND_DISCONNECT:
                connection->state = SENT_DISCONNECT;
                hci_send_cmd(&hci_disconnect, connection->con_handle, 0x13); // remote closed connection
                return;

            default:
                break;
        }

        if (connection->authentication_flags & HANDLE_LINK_KEY_REQUEST){
            log_info("responding to link key request");
            connectionClearAuthenticationFlags(connection, HANDLE_LINK_KEY_REQUEST);
            link_key_t link_key;
            link_key_type_t link_key_type;
            if ( hci_stack->remote_device_db
              && hci_stack->remote_device_db->get_link_key( &connection->address, &link_key, &link_key_type)
              && gap_security_level_for_link_key_type(link_key_type) >= connection->requested_security_level){
               connection->link_key_type = link_key_type;
               hci_send_cmd(&hci_link_key_request_reply, connection->address, &link_key);
            } else {
               hci_send_cmd(&hci_link_key_request_negative_reply, connection->address);
            }
            return;
        }

        if (connection->authentication_flags & DENY_PIN_CODE_REQUEST){
            log_info("denying to pin request");
            connectionClearAuthenticationFlags(connection, DENY_PIN_CODE_REQUEST);
            hci_send_cmd(&hci_pin_code_request_negative_reply, connection->address);
            return;
        }

        if (connection->authentication_flags & SEND_IO_CAPABILITIES_REPLY){
            connectionClearAuthenticationFlags(connection, SEND_IO_CAPABILITIES_REPLY);
            log_info("IO Capability Request received, stack bondable %u, io cap %u", hci_stack->bondable, hci_stack->ssp_io_capability);
            if (hci_stack->bondable && (hci_stack->ssp_io_capability != SSP_IO_CAPABILITY_UNKNOWN)){
                // tweak authentication requirements
                uint8_t authreq = hci_stack->ssp_authentication_requirement;
                if (connection->bonding_flags & BONDING_DEDICATED){
                    authreq = SSP_IO_AUTHREQ_MITM_PROTECTION_NOT_REQUIRED_DEDICATED_BONDING;
                }
                if (gap_mitm_protection_required_for_security_level(connection->requested_security_level)){
                    authreq |= 1;
                }
                hci_send_cmd(&hci_io_capability_request_reply, &connection->address, hci_stack->ssp_io_capability, NULL, authreq);
            } else {
                hci_send_cmd(&hci_io_capability_request_negative_reply, &connection->address, ERROR_CODE_PAIRING_NOT_ALLOWED);
            }
            return;
        }

        if (connection->authentication_flags & SEND_USER_CONFIRM_REPLY){
            connectionClearAuthenticationFlags(connection, SEND_USER_CONFIRM_REPLY);
            hci_send_cmd(&hci_user_confirmation_request_reply, &connection->address);
            return;
        }

        if (connection->authentication_flags & SEND_USER_PASSKEY_REPLY){
            connectionClearAuthenticationFlags(connection, SEND_USER_PASSKEY_REPLY);
            hci_send_cmd(&hci_user_passkey_request_reply, &connection->address, 000000);
            return;
        }

        if (connection->bonding_flags & BONDING_REQUEST_REMOTE_FEATURES){
            connection->bonding_flags &= ~BONDING_REQUEST_REMOTE_FEATURES;
            hci_send_cmd(&hci_read_remote_supported_features_command, connection->con_handle);
            return;
        }

        if (connection->bonding_flags & BONDING_DISCONNECT_SECURITY_BLOCK){
            connection->bonding_flags &= ~BONDING_DISCONNECT_SECURITY_BLOCK;
            hci_send_cmd(&hci_disconnect, connection->con_handle, 0x0005);  // authentication failure
            return;
        }
        if (connection->bonding_flags & BONDING_DISCONNECT_DEDICATED_DONE){
            connection->bonding_flags &= ~BONDING_DISCONNECT_DEDICATED_DONE;
            connection->bonding_flags |= BONDING_EMIT_COMPLETE_ON_DISCONNECT;
            hci_send_cmd(&hci_disconnect, connection->con_handle, 0x13);  // authentication done
            return;
        }
        if (connection->bonding_flags & BONDING_SEND_AUTHENTICATE_REQUEST){
            connection->bonding_flags &= ~BONDING_SEND_AUTHENTICATE_REQUEST;
            hci_send_cmd(&hci_authentication_requested, connection->con_handle);
            return;
        }
        if (connection->bonding_flags & BONDING_SEND_ENCRYPTION_REQUEST){
            connection->bonding_flags &= ~BONDING_SEND_ENCRYPTION_REQUEST;
            hci_send_cmd(&hci_set_connection_encryption, connection->con_handle, 1);
            return;
        }

#ifdef HAVE_BLE
        if (connection->le_con_parameter_update_state == CON_PARAMETER_UPDATE_CHANGE_HCI_CON_PARAMETERS){
            connection->le_con_parameter_update_state = CON_PARAMETER_UPDATE_NONE;

            uint16_t connection_interval_min = connection->le_conn_interval_min;
            connection->le_conn_interval_min = 0;
            hci_send_cmd(&hci_le_connection_update, connection->con_handle, connection_interval_min,
                connection->le_conn_interval_max, connection->le_conn_latency, connection->le_supervision_timeout,
                0x0000, 0xffff);
        }
#endif
    }

    switch (hci_stack->state){
        case HCI_STATE_INITIALIZING:
            hci_initializing_state_machine();
            break;

        case HCI_STATE_HALTING:

            log_info("HCI_STATE_HALTING");
            // close all open connections
            connection =  (hci_connection_t *) hci_stack->connections;
            if (connection){

                // send disconnect
                if (!hci_can_send_command_packet_now()) return;

                log_info("HCI_STATE_HALTING, connection %p, handle %u", connection, (uint16_t)connection->con_handle);
                hci_send_cmd(&hci_disconnect, connection->con_handle, 0x13);  // remote closed connection

                // send disconnected event right away - causes higher layer connections to get closed, too.
                hci_shutdown_connection(connection);
                return;
            }
            log_info("HCI_STATE_HALTING, calling off");

            // switch mode
            hci_power_control_off();

            log_info("HCI_STATE_HALTING, emitting state");
            hci_emit_state();
            log_info("HCI_STATE_HALTING, done");
            break;

        case HCI_STATE_FALLING_ASLEEP:
            switch(hci_stack->substate) {
                case 0:
                    log_info("HCI_STATE_FALLING_ASLEEP");
                    // close all open connections
                    connection =  (hci_connection_t *) hci_stack->connections;

#if defined(USE_POWERMANAGEMENT) && defined(USE_BLUETOOL)
                    // don't close connections, if H4 supports power management
                    if (bt_control_iphone_power_management_enabled()){
                        connection = NULL;
                    }
#endif
                    if (connection){

                        // send disconnect
                        if (!hci_can_send_command_packet_now()) return;

                        log_info("HCI_STATE_FALLING_ASLEEP, connection %p, handle %u", connection, (uint16_t)connection->con_handle);
                        hci_send_cmd(&hci_disconnect, connection->con_handle, 0x13);  // remote closed connection

                        // send disconnected event right away - causes higher layer connections to get closed, too.
                        hci_shutdown_connection(connection);
                        return;
                    }

                    if (hci_classic_supported()){
                        // disable page and inquiry scan
                        if (!hci_can_send_command_packet_now()) return;

                        log_info("HCI_STATE_HALTING, disabling inq scans");
                        hci_send_cmd(&hci_write_scan_enable, hci_stack->connectable << 1); // drop inquiry scan but keep page scan

                        // continue in next sub state
                        hci_stack->substate++;
                        break;
                    }
                    // fall through for ble-only chips

                case 2:
                    log_info("HCI_STATE_HALTING, calling sleep");
#if defined(USE_POWERMANAGEMENT) && defined(USE_BLUETOOL)
                    // don't actually go to sleep, if H4 supports power management
                    if (bt_control_iphone_power_management_enabled()){
                        // SLEEP MODE reached
                        hci_stack->state = HCI_STATE_SLEEPING;
                        hci_emit_state();
                        break;
                    }
#endif
                    // switch mode
                    hci_power_control_sleep();  // changes hci_stack->state to SLEEP
                    hci_emit_state();
                    break;

                default:
                    break;
            }
            break;

        default:
            break;
    }
}

int hci_send_cmd_packet(uint8_t *packet, int size){
    bd_addr_t addr;
    hci_connection_t * conn;
    // house-keeping

    // create_connection?
    if (IS_COMMAND(packet, hci_create_connection)){
        bt_flip_addr(addr, &packet[3]);
        log_info("Create_connection to %s", bd_addr_to_str(addr));

        conn = hci_connection_for_bd_addr_and_type(&addr, BD_ADDR_TYPE_CLASSIC);
        if (!conn){
            conn = create_connection_for_bd_addr_and_type(addr, BD_ADDR_TYPE_CLASSIC);
            if (!conn){
                // notify client that alloc failed
                hci_emit_connection_complete(conn, BTSTACK_MEMORY_ALLOC_FAILED);
                return 0; // don't sent packet to controller
            }
            conn->state = SEND_CREATE_CONNECTION;
        }
        log_info("conn state %u", conn->state);
        switch (conn->state){
            // if connection active exists
            case OPEN:
                // and OPEN, emit connection complete command, don't send to controller
                hci_emit_connection_complete(conn, 0);
                return 0;
            case SEND_CREATE_CONNECTION:
                // connection created by hci, e.g. dedicated bonding
                break;
            default:
                // otherwise, just ignore as it is already in the open process
                return 0;
        }
        conn->state = SENT_CREATE_CONNECTION;
    }
    if (IS_COMMAND(packet, hci_link_key_request_reply)){
        hci_add_connection_flags_for_flipped_bd_addr(&packet[3], SENT_LINK_KEY_REPLY);
    }
    if (IS_COMMAND(packet, hci_link_key_request_negative_reply)){
        hci_add_connection_flags_for_flipped_bd_addr(&packet[3], SENT_LINK_KEY_NEGATIVE_REQUEST);
    }

    if (IS_COMMAND(packet, hci_delete_stored_link_key)){
        if (hci_stack->remote_device_db){
            bt_flip_addr(addr, &packet[3]);
            hci_stack->remote_device_db->delete_link_key(&addr);
        }
    }

    if (IS_COMMAND(packet, hci_pin_code_request_negative_reply)
    ||  IS_COMMAND(packet, hci_pin_code_request_reply)){
        bt_flip_addr(addr, &packet[3]);
        conn = hci_connection_for_bd_addr_and_type(&addr, BD_ADDR_TYPE_CLASSIC);
        if (conn){
            connectionClearAuthenticationFlags(conn, LEGACY_PAIRING_ACTIVE);
        }
    }

    if (IS_COMMAND(packet, hci_user_confirmation_request_negative_reply)
    ||  IS_COMMAND(packet, hci_user_confirmation_request_reply)
    ||  IS_COMMAND(packet, hci_user_passkey_request_negative_reply)
    ||  IS_COMMAND(packet, hci_user_passkey_request_reply)) {
        bt_flip_addr(addr, &packet[3]);
        conn = hci_connection_for_bd_addr_and_type(&addr, BD_ADDR_TYPE_CLASSIC);
        if (conn){
            connectionClearAuthenticationFlags(conn, SSP_PAIRING_ACTIVE);
        }
    }

#ifdef HAVE_BLE
    if (IS_COMMAND(packet, hci_le_set_advertising_parameters)){
        hci_stack->adv_addr_type = packet[8];
    }
    if (IS_COMMAND(packet, hci_le_set_random_address)){
        bt_flip_addr(hci_stack->adv_address, &packet[3]);
    }
#endif

    hci_stack->num_cmd_packets--;

    hci_dump_packet(HCI_COMMAND_DATA_PACKET, 0, packet, size);
    int err = hci_stack->hci_transport->send_packet(HCI_COMMAND_DATA_PACKET, packet, size);

    // release packet buffer for synchronous transport implementations
    if (hci_transport_synchronous() && (packet == hci_stack->hci_packet_buffer)){
        hci_stack->hci_packet_buffer_reserved = 0;
    }

    return err;
}

// disconnect because of security block
void hci_disconnect_security_block(hci_con_handle_t con_handle){
    hci_connection_t * connection = hci_connection_for_handle(con_handle);
    if (!connection) return;
    connection->bonding_flags |= BONDING_DISCONNECT_SECURITY_BLOCK;
}


// Configure Secure Simple Pairing

// enable will enable SSP during init
void hci_ssp_set_enable(int enable){
    hci_stack->ssp_enable = enable;
}

int hci_local_ssp_activated(){
    return hci_ssp_supported() && hci_stack->ssp_enable;
}

// if set, BTstack will respond to io capability request using authentication requirement
void hci_ssp_set_io_capability(int io_capability){
    hci_stack->ssp_io_capability = io_capability;
}
void hci_ssp_set_authentication_requirement(int authentication_requirement){
    hci_stack->ssp_authentication_requirement = authentication_requirement;
}

// if set, BTstack will confirm a numberic comparion and enter '000000' if requested
void hci_ssp_set_auto_accept(int auto_accept){
    hci_stack->ssp_auto_accept = auto_accept;
}

/**
 * pre: numcmds >= 0 - it's allowed to send a command to the controller
 */
int hci_send_cmd(const hci_cmd_t *cmd, ...){

    if (!hci_can_send_command_packet_now()){
        log_error("hci_send_cmd called but cannot send packet now");
        return 0;
    }

    // for HCI INITIALIZATION
    // log_info("hci_send_cmd: opcode %04x", cmd->opcode);
    hci_stack->last_cmd_opcode = cmd->opcode;

    hci_reserve_packet_buffer();
    uint8_t * packet = hci_stack->hci_packet_buffer;

    va_list argptr;
    va_start(argptr, cmd);
    uint16_t size = hci_create_cmd_internal(packet, cmd, argptr);
    va_end(argptr);

    return hci_send_cmd_packet(packet, size);
}

// Create various non-HCI events.
// TODO: generalize, use table similar to hci_create_command

void hci_emit_state(){
    log_info("BTSTACK_EVENT_STATE %u", hci_stack->state);
    uint8_t event[3];
    event[0] = BTSTACK_EVENT_STATE;
    event[1] = sizeof(event) - 2;
    event[2] = hci_stack->state;
    hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_connection_complete(hci_connection_t *conn, uint8_t status){
    uint8_t event[13];
    event[0] = HCI_EVENT_CONNECTION_COMPLETE;
    event[1] = sizeof(event) - 2;
    event[2] = status;
    bt_store_16(event, 3, conn->con_handle);
    bt_flip_addr(&event[5], conn->address);
    event[11] = 1; // ACL connection
    event[12] = 0; // encryption disabled
    hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_le_connection_complete(uint8_t address_type, bd_addr_t * address, uint16_t conn_handle, uint8_t status){
    uint8_t event[21];
    event[0] = HCI_EVENT_LE_META;
    event[1] = sizeof(event) - 2;
    event[2] = HCI_SUBEVENT_LE_CONNECTION_COMPLETE;
    event[3] = status;
    bt_store_16(event, 4, conn_handle);
    event[6] = 0; // TODO: role
    event[7] = address_type;
    bt_flip_addr(&event[8], *address);
    bt_store_16(event, 14, 0); // interval
    bt_store_16(event, 16, 0); // latency
    bt_store_16(event, 18, 0); // supervision timeout
    event[20] = 0; // master clock accuracy
    hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_disconnection_complete(uint16_t handle, uint8_t reason){
    uint8_t event[6];
    event[0] = HCI_EVENT_DISCONNECTION_COMPLETE;
    event[1] = sizeof(event) - 2;
    event[2] = 0; // status = OK
    bt_store_16(event, 3, handle);
    event[5] = reason;
    hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_l2cap_check_timeout(hci_connection_t *conn){
    if (disable_l2cap_timeouts) return;
    log_info("L2CAP_EVENT_TIMEOUT_CHECK");
    uint8_t event[4];
    event[0] = L2CAP_EVENT_TIMEOUT_CHECK;
    event[1] = sizeof(event) - 2;
    bt_store_16(event, 2, conn->con_handle);
    hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_nr_connections_changed(){
    log_info("BTSTACK_EVENT_NR_CONNECTIONS_CHANGED %u", nr_hci_connections());
    uint8_t event[3];
    event[0] = BTSTACK_EVENT_NR_CONNECTIONS_CHANGED;
    event[1] = sizeof(event) - 2;
    event[2] = nr_hci_connections();
    hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_hci_open_failed(){
    log_info("BTSTACK_EVENT_POWERON_FAILED");
    uint8_t event[2];
    event[0] = BTSTACK_EVENT_POWERON_FAILED;
    event[1] = sizeof(event) - 2;
    hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

#ifndef EMBEDDED
void hci_emit_btstack_version() {
    log_info("BTSTACK_EVENT_VERSION %u.%u", BTSTACK_MAJOR, BTSTACK_MINOR);
    uint8_t event[6];
    event[0] = BTSTACK_EVENT_VERSION;
    event[1] = sizeof(event) - 2;
    event[2] = BTSTACK_MAJOR;
    event[3] = BTSTACK_MINOR;
    bt_store_16(event, 4, BTSTACK_REVISION);
    hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}
#endif

void hci_emit_system_bluetooth_enabled(uint8_t enabled){
    log_info("BTSTACK_EVENT_SYSTEM_BLUETOOTH_ENABLED %u", enabled);
    uint8_t event[3];
    event[0] = BTSTACK_EVENT_SYSTEM_BLUETOOTH_ENABLED;
    event[1] = sizeof(event) - 2;
    event[2] = enabled;
    hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_remote_name_cached(bd_addr_t *addr, device_name_t *name){
    uint8_t event[2+1+6+248+1]; // +1 for \0 in log_info
    event[0] = BTSTACK_EVENT_REMOTE_NAME_CACHED;
    event[1] = sizeof(event) - 2 - 1;
    event[2] = 0;   // just to be compatible with HCI_EVENT_REMOTE_NAME_REQUEST_COMPLETE
    bt_flip_addr(&event[3], *addr);
    memcpy(&event[9], name, 248);

    event[9+248] = 0;   // assert \0 for log_info
    log_info("BTSTACK_EVENT_REMOTE_NAME_CACHED %s = '%s'", bd_addr_to_str(*addr), &event[9]);

    hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event)-1);
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event)-1);
}

void hci_emit_discoverable_enabled(uint8_t enabled){
    log_info("BTSTACK_EVENT_DISCOVERABLE_ENABLED %u", enabled);
    uint8_t event[3];
    event[0] = BTSTACK_EVENT_DISCOVERABLE_ENABLED;
    event[1] = sizeof(event) - 2;
    event[2] = enabled;
    hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_security_level(hci_con_handle_t con_handle, gap_security_level_t level){
    log_info("hci_emit_security_level %u for handle %x", level, con_handle);
    uint8_t event[5];
    int pos = 0;
    event[pos++] = GAP_SECURITY_LEVEL;
    event[pos++] = sizeof(event) - 2;
    bt_store_16(event, 2, con_handle);
    pos += 2;
    event[pos++] = level;
    hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

void hci_emit_dedicated_bonding_result(bd_addr_t address, uint8_t status){
    log_info("hci_emit_dedicated_bonding_result %u ", status);
    uint8_t event[9];
    int pos = 0;
    event[pos++] = GAP_DEDICATED_BONDING_COMPLETED;
    event[pos++] = sizeof(event) - 2;
    event[pos++] = status;
    bt_flip_addr( * (bd_addr_t *) &event[pos], address);
    pos += 6;
    hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
    hci_stack->packet_handler(HCI_EVENT_PACKET, event, sizeof(event));
}

// query if remote side supports SSP
int hci_remote_ssp_supported(hci_con_handle_t con_handle){
    hci_connection_t * connection = hci_connection_for_handle(con_handle);
    if (!connection) return 0;
    return (connection->bonding_flags & BONDING_REMOTE_SUPPORTS_SSP) ? 1 : 0;
}

int hci_ssp_supported_on_both_sides(hci_con_handle_t handle){
    return hci_local_ssp_activated() && hci_remote_ssp_supported(handle);
}

// GAP API
/**
 * @bbrief enable/disable bonding. default is enabled
 * @praram enabled
 */
void gap_set_bondable_mode(int enable){
    hci_stack->bondable = enable ? 1 : 0;
}

/**
 * @brief map link keys to security levels
 */
gap_security_level_t gap_security_level_for_link_key_type(link_key_type_t link_key_type){
    switch (link_key_type){
        case AUTHENTICATED_COMBINATION_KEY_GENERATED_FROM_P256:
            return LEVEL_4;
        case COMBINATION_KEY:
        case AUTHENTICATED_COMBINATION_KEY_GENERATED_FROM_P192:
            return LEVEL_3;
        default:
            return LEVEL_2;
    }
}

static gap_security_level_t gap_security_level_for_connection(hci_connection_t * connection){
    if (!connection) return LEVEL_0;
    if ((connection->authentication_flags & CONNECTION_ENCRYPTED) == 0) return LEVEL_0;
    return gap_security_level_for_link_key_type(connection->link_key_type);
}


int gap_mitm_protection_required_for_security_level(gap_security_level_t level){
    log_info("gap_mitm_protection_required_for_security_level %u", level);
    return level > LEVEL_2;
}

/**
 * @brief get current security level
 */
gap_security_level_t gap_security_level(hci_con_handle_t con_handle){
    hci_connection_t * connection = hci_connection_for_handle(con_handle);
    if (!connection) return LEVEL_0;
    return gap_security_level_for_connection(connection);
}

/**
 * @brief request connection to device to
 * @result GAP_AUTHENTICATION_RESULT
 */
void gap_request_security_level(hci_con_handle_t con_handle, gap_security_level_t requested_level){
    hci_connection_t * connection = hci_connection_for_handle(con_handle);
    if (!connection){
        hci_emit_security_level(con_handle, LEVEL_0);
        return;
    }
    gap_security_level_t current_level = gap_security_level(con_handle);
    log_info("gap_request_security_level %u, current level %u", requested_level, current_level);
    if (current_level >= requested_level){
        hci_emit_security_level(con_handle, current_level);
        return;
    }

    connection->requested_security_level = requested_level;

#if 0
    // sending encryption request without a link key results in an error.
    // TODO: figure out how to use it properly

    // would enabling ecnryption suffice (>= LEVEL_2)?
    if (hci_stack->remote_device_db){
        link_key_type_t link_key_type;
        link_key_t      link_key;
        if (hci_stack->remote_device_db->get_link_key( &connection->address, &link_key, &link_key_type)){
            if (gap_security_level_for_link_key_type(link_key_type) >= requested_level){
                connection->bonding_flags |= BONDING_SEND_ENCRYPTION_REQUEST;
                return;
            }
        }
    }
#endif

    // try to authenticate connection
    connection->bonding_flags |= BONDING_SEND_AUTHENTICATE_REQUEST;
    hci_run();
}

/**
 * @brief start dedicated bonding with device. disconnect after bonding
 * @param device
 * @param request MITM protection
 * @result GAP_DEDICATED_BONDING_COMPLETE
 */
int gap_dedicated_bonding(bd_addr_t device, int mitm_protection_required){

    // create connection state machine
    hci_connection_t * connection = create_connection_for_bd_addr_and_type(device, BD_ADDR_TYPE_CLASSIC);

    if (!connection){
        return BTSTACK_MEMORY_ALLOC_FAILED;
    }

    // delete linkn key
    hci_drop_link_key_for_bd_addr( (bd_addr_t *) &device);

    // configure LEVEL_2/3, dedicated bonding
    connection->state = SEND_CREATE_CONNECTION;
    connection->requested_security_level = mitm_protection_required ? LEVEL_3 : LEVEL_2;
    log_info("gap_dedicated_bonding, mitm %u -> level %u", mitm_protection_required, connection->requested_security_level);
    connection->bonding_flags = BONDING_DEDICATED;

    // wait for GAP Security Result and send GAP Dedicated Bonding complete

    // handle: connnection failure (connection complete != ok)
    // handle: authentication failure
    // handle: disconnect on done

    hci_run();

    return 0;
}

void gap_set_local_name(const char * local_name){
    hci_stack->local_name = local_name;
}

le_command_status_t le_central_start_scan(){
    if (hci_stack->le_scanning_state == LE_SCANNING) return BLE_PERIPHERAL_OK;
    hci_stack->le_scanning_state = LE_START_SCAN;
    hci_run();
    return BLE_PERIPHERAL_OK;
}

le_command_status_t le_central_stop_scan(){
    if ( hci_stack->le_scanning_state == LE_SCAN_IDLE) return BLE_PERIPHERAL_OK;
    hci_stack->le_scanning_state = LE_STOP_SCAN;
    hci_run();
    return BLE_PERIPHERAL_OK;
}

void le_central_set_scan_parameters(uint8_t scan_type, uint16_t scan_interval, uint16_t scan_window){
    hci_stack->le_scan_type     = scan_type;
    hci_stack->le_scan_interval = scan_interval;
    hci_stack->le_scan_window   = scan_window;
    hci_run();
}

le_command_status_t le_central_connect(bd_addr_t * addr, bd_addr_type_t addr_type){
    hci_connection_t * conn = hci_connection_for_bd_addr_and_type(addr, addr_type);
    if (!conn){
        log_info("le_central_connect: no connection exists yet, creating context");
        conn = create_connection_for_bd_addr_and_type(*addr, addr_type);
        if (!conn){
            // notify client that alloc failed
            hci_emit_le_connection_complete(addr_type, addr, 0, BTSTACK_MEMORY_ALLOC_FAILED);
            log_info("le_central_connect: failed to alloc hci_connection_t");
            return BLE_PERIPHERAL_NOT_CONNECTED; // don't sent packet to controller
        }
        conn->state = SEND_CREATE_CONNECTION;
        log_info("le_central_connect: send create connection next");
        hci_run();
        return BLE_PERIPHERAL_OK;
    }

    if (!hci_is_le_connection(conn) ||
        conn->state == SEND_CREATE_CONNECTION ||
        conn->state == SENT_CREATE_CONNECTION) {
        hci_emit_le_connection_complete(conn->address_type, &conn->address, 0, ERROR_CODE_COMMAND_DISALLOWED);
        log_error("le_central_connect: classic connection or connect is already being created");
        return BLE_PERIPHERAL_IN_WRONG_STATE;
    }

    log_info("le_central_connect: context exists with state %u", conn->state);
    hci_emit_le_connection_complete(conn->address_type, &conn->address, conn->con_handle, 0);
    hci_run();
    return BLE_PERIPHERAL_OK;
}

// @assumption: only a single outgoing LE Connection exists
static hci_connection_t * le_central_get_outgoing_connection(){
    linked_item_t *it;
    for (it = (linked_item_t *) hci_stack->connections; it ; it = it->next){
        hci_connection_t * conn = (hci_connection_t *) it;
        if (!hci_is_le_connection(conn)) continue;
        switch (conn->state){
            case SEND_CREATE_CONNECTION:
            case SENT_CREATE_CONNECTION:
                return conn;
            default:
                break;
        };
    }
    return NULL;
}

le_command_status_t le_central_connect_cancel(){
    hci_connection_t * conn = le_central_get_outgoing_connection();
    switch (conn->state){
        case SEND_CREATE_CONNECTION:
            // skip sending create connection and emit event instead
            hci_emit_le_connection_complete(conn->address_type, &conn->address, 0, ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER);
            linked_list_remove(&hci_stack->connections, (linked_item_t *) conn);
            btstack_memory_hci_connection_free( conn );
            break;
        case SENT_CREATE_CONNECTION:
            // request to send cancel connection
            conn->state = SEND_CANCEL_CONNECTION;
            hci_run();
            break;
        default:
            break;
    }
    return BLE_PERIPHERAL_OK;
}

/**
 * @brief Updates the connection parameters for a given LE connection
 * @param handle
 * @param conn_interval_min (unit: 1.25ms)
 * @param conn_interval_max (unit: 1.25ms)
 * @param conn_latency
 * @param supervision_timeout (unit: 10ms)
 * @returns 0 if ok
 */
int gap_update_connection_parameters(hci_con_handle_t con_handle, uint16_t conn_interval_min,
    uint16_t conn_interval_max, uint16_t conn_latency, uint16_t supervision_timeout){
    hci_connection_t * connection = hci_connection_for_handle(con_handle);
    if (!connection) return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    connection->le_conn_interval_min = conn_interval_min;
    connection->le_conn_interval_max = conn_interval_max;
    connection->le_conn_latency = conn_latency;
    connection->le_supervision_timeout = supervision_timeout;
    return 0;
}

le_command_status_t gap_disconnect(hci_con_handle_t handle){
    hci_connection_t * conn = hci_connection_for_handle(handle);
    if (!conn){
        hci_emit_disconnection_complete(handle, 0);
        return BLE_PERIPHERAL_OK;
    }
    conn->state = SEND_DISCONNECT;
    hci_run();
    return BLE_PERIPHERAL_OK;
}

void hci_disconnect_all(){
    linked_list_iterator_t it;
    linked_list_iterator_init(&it, &hci_stack->connections);
    while (linked_list_iterator_has_next(&it)){
        hci_connection_t * con = (hci_connection_t*) linked_list_iterator_next(&it);
        if (con->state == SENT_DISCONNECT) continue;
        con->state = SEND_DISCONNECT;
    }
    hci_run();
}