xref: /btstack/src/hci_transport_h5.c (revision 94764e99109946c1973cdfe0920944746421fced)

/*
 * Copyright (C) 2016 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
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 * Please inquire about commercial licensing options at
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 */

/*
 *  hci_transport_h5.c
 *
 *  HCI Transport API implementation for basic H5 protocol
 *
 *  Created by Matthias Ringwald on 4/29/09.
 */

#include "hci.h"
#include "btstack_slip.h"
#include "btstack_debug.h"
#include "hci_transport.h"
#include "btstack_uart_block.h"

typedef enum {
    LINK_UNINITIALIZED,
    LINK_INITIALIZED,
    LINK_ACTIVE
} hci_transport_link_state_t;

typedef enum {
    HCI_TRANSPORT_LINK_SEND_SYNC            = 1 << 0,
    HCI_TRANSPORT_LINK_SEND_SYNC_RESPONSE   = 1 << 1,
    HCI_TRANSPORT_LINK_SEND_CONFIG          = 1 << 2,
    HCI_TRANSPORT_LINK_SEND_CONFIG_RESPONSE = 1 << 3,
    HCI_TRANSPORT_LINK_SEND_SLEEP           = 1 << 4,
    HCI_TRANSPORT_LINK_SEND_WOKEN           = 1 << 5,
    HCI_TRANSPORT_LINK_SEND_WAKEUP          = 1 << 6,
    HCI_TRANSPORT_LINK_SEND_QUEUED_PACKET   = 1 << 7,
    HCI_TRANSPORT_LINK_SEND_ACK_PACKET      = 1 << 8,
    HCI_TRANSPORT_LINK_ENTER_SLEEP          = 1 << 9,

} hci_transport_link_actions_t;

// Configuration Field. No packet buffers -> sliding window = 1, no OOF flow control, no data integrity check
#define LINK_CONFIG_SLIDING_WINDOW_SIZE 1
#define LINK_CONFIG_OOF_FLOW_CONTROL 0
#define LINK_CONFIG_DATA_INTEGRITY_CHECK 0
#define LINK_CONFIG_VERSION_NR 0
#define LINK_CONFIG_FIELD (LINK_CONFIG_SLIDING_WINDOW_SIZE | (LINK_CONFIG_OOF_FLOW_CONTROL << 3) | (LINK_CONFIG_DATA_INTEGRITY_CHECK << 4) | (LINK_CONFIG_VERSION_NR << 5))

// periodic sending during link establishment
#define LINK_PERIOD_MS 250

// resend wakeup
#define LINK_WAKEUP_MS 50

// additional packet types
#define LINK_ACKNOWLEDGEMENT_TYPE 0x00
#define LINK_CONTROL_PACKET_TYPE 0x0f

// ---
static const uint8_t link_control_sync[] =   { 0x01, 0x7e};
static const uint8_t link_control_sync_response[] = { 0x02, 0x7d};
static const uint8_t link_control_config[] = { 0x03, 0xfc, LINK_CONFIG_FIELD};
static const uint8_t link_control_config_prefix_len  = 2;
static const uint8_t link_control_config_response[] = { 0x04, 0x7b, LINK_CONFIG_FIELD};
static const uint8_t link_control_config_response_prefix_len  = 2;
static const uint8_t link_control_wakeup[] = { 0x05, 0xfa};
static const uint8_t link_control_woken[] =  { 0x06, 0xf9};
static const uint8_t link_control_sleep[] =  { 0x07, 0x78};

// incoming pre-bufffer + 4 bytes H5 header + max(acl header + acl payload, event header + event data) + 2 bytes opt CRC
static uint8_t   hci_packet_with_pre_buffer[HCI_INCOMING_PRE_BUFFER_SIZE + 6 + HCI_PACKET_BUFFER_SIZE];

// Non-optimized outgoing buffer (EOF, 4 bytes header, payload, EOF)
static uint8_t slip_outgoing_buffer[2 + 2 * (HCI_PACKET_BUFFER_SIZE + 4)];

// H5 Link State
static hci_transport_link_state_t link_state;
static btstack_timer_source_t link_timer;
static uint8_t  link_seq_nr;
static uint8_t  link_ack_nr;
static uint16_t link_resend_timeout_ms;
static uint8_t  link_peer_asleep;

// auto sleep-mode
static btstack_timer_source_t inactivity_timer;
static uint16_t link_inactivity_timeout_ms; // auto-sleep if set

// Outgoing packet
static uint8_t   hci_packet_type;
static uint16_t  hci_packet_size;
static uint8_t * hci_packet;

// hci packet handler
static  void (*packet_handler)(uint8_t packet_type, uint8_t *packet, uint16_t size);

static int hci_transport_link_actions;

// UART Driver + Config
static const btstack_uart_block_t * btstack_uart;
static btstack_uart_config_t uart_config;
static btstack_uart_sleep_mode_t btstack_uart_sleep_mode;

static int uart_write_active;

// Prototypes
static void hci_transport_h5_process_frame(uint16_t frame_size);
static int  hci_transport_link_have_outgoing_packet(void);
static void hci_transport_link_send_queued_packet(void);
static void hci_transport_link_set_timer(uint16_t timeout_ms);
static void hci_transport_link_timeout_handler(btstack_timer_source_t * timer);
static void hci_transport_link_run(void);
static void hci_transport_slip_init(void);

// -----------------------------
static void hci_transport_inactivity_timeout_handler(btstack_timer_source_t * ts){
    log_info("h5: inactivity timeout. link state %u, peer asleep %u, actions 0x%02x, outgoing packet %u",
        link_state, link_peer_asleep, hci_transport_link_actions, hci_transport_link_have_outgoing_packet());
    if (hci_transport_link_have_outgoing_packet()) return;
    if (link_state != LINK_ACTIVE) return;
    if (hci_transport_link_actions) return;
    if (link_peer_asleep) return;
    hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_SLEEP;
    hci_transport_link_run();
}

static void hci_transport_inactivity_timer_set(void){
    if (!link_inactivity_timeout_ms) return;
    btstack_run_loop_set_timer_handler(&inactivity_timer, &hci_transport_inactivity_timeout_handler);
    btstack_run_loop_set_timer(&inactivity_timer, link_inactivity_timeout_ms);
    btstack_run_loop_remove_timer(&inactivity_timer);
    btstack_run_loop_add_timer(&inactivity_timer);
}

// -----------------------------
// SLIP Outgoing

// format: 0xc0 HEADER PACKER 0xc0
// @param uint8_t header[4]
static void hci_transport_slip_send_frame(const uint8_t * header, const uint8_t * packet, uint16_t packet_size){

    int pos = 0;

    // Start of Frame
    slip_outgoing_buffer[pos++] = BTSTACK_SLIP_SOF;

    // Header
    btstack_slip_encoder_start(header, 4);
    while (btstack_slip_encoder_has_data()){
        slip_outgoing_buffer[pos++] = btstack_slip_encoder_get_byte();
    }

    // Packet
    btstack_slip_encoder_start(packet, packet_size);
    while (btstack_slip_encoder_has_data()){
        slip_outgoing_buffer[pos++] = btstack_slip_encoder_get_byte();
    }

    // Start of Frame
    slip_outgoing_buffer[pos++] = BTSTACK_SLIP_SOF;

    uart_write_active = 1;
    btstack_uart->send_block(slip_outgoing_buffer, pos);
}

// SLIP Incoming

static void hci_transport_slip_init(void){
    btstack_slip_decoder_init(&hci_packet_with_pre_buffer[HCI_INCOMING_PRE_BUFFER_SIZE], 6 + HCI_PACKET_BUFFER_SIZE);
}

// H5 Three-Wire Implementation

static void hci_transport_link_calc_header(uint8_t * header,
    uint8_t  sequence_nr,
    uint8_t  acknowledgement_nr,
    uint8_t  data_integrity_check_present,
    uint8_t  reliable_packet,
    uint8_t  packet_type,
    uint16_t payload_length){

    // reset data integrity flag
    if (data_integrity_check_present){
        log_error("hci_transport_link_calc_header: data integrity not supported, dropping flag");
        data_integrity_check_present = 0;
    }

    header[0] = sequence_nr | (acknowledgement_nr << 3) | (data_integrity_check_present << 6) | (reliable_packet << 7);
    header[1] = packet_type | ((payload_length & 0x0f) << 4);
    header[2] = payload_length >> 4;
    header[3] = 0xff - (header[0] + header[1] + header[2]);
}

static void hci_transport_link_send_control(const uint8_t * message, int message_len){
    uint8_t header[4];
    hci_transport_link_calc_header(header, 0, 0, 0, 0, LINK_CONTROL_PACKET_TYPE, message_len);
    hci_transport_slip_send_frame(header, message, message_len);
}

static void hci_transport_link_send_sync(void){
    log_info("link: send sync");
    hci_transport_link_send_control(link_control_sync, sizeof(link_control_sync));
}

static void hci_transport_link_send_sync_response(void){
    log_info("link: send sync response");
    hci_transport_link_send_control(link_control_sync_response, sizeof(link_control_sync_response));
}

static void hci_transport_link_send_config(void){
    log_info("link: send config");
    hci_transport_link_send_control(link_control_config, sizeof(link_control_config));
}

static void hci_transport_link_send_config_response(void){
    log_info("link: send config response");
    hci_transport_link_send_control(link_control_config_response, sizeof(link_control_config_response));
}

static void hci_transport_link_send_woken(void){
    log_info("link: send woken");
    hci_transport_link_send_control(link_control_woken, sizeof(link_control_woken));
}

static void hci_transport_link_send_wakeup(void){
    log_info("link: send wakeup");
    hci_transport_link_send_control(link_control_wakeup, sizeof(link_control_wakeup));
}

static void hci_transport_link_send_sleep(void){
    log_info("link: send sleep");
    hci_transport_link_send_control(link_control_sleep, sizeof(link_control_sleep));
}

static void hci_transport_link_send_queued_packet(void){
    log_info("hci_transport_link_send_queued_packet: seq %u, ack %u, size %u", link_seq_nr, link_ack_nr, hci_packet_size);
    log_info_hexdump(hci_packet, hci_packet_size);

    uint8_t header[4];
    hci_transport_link_calc_header(header, link_seq_nr, link_ack_nr, 0, 1, hci_packet_type, hci_packet_size);
    hci_transport_slip_send_frame(header, hci_packet, hci_packet_size);

    // reset inactvitiy timer
    hci_transport_inactivity_timer_set();
}

static void hci_transport_link_send_ack_packet(void){
    log_info("link: send ack %u", link_ack_nr);
    uint8_t header[4];
    hci_transport_link_calc_header(header, 0, link_ack_nr, 0, 0, LINK_ACKNOWLEDGEMENT_TYPE, 0);
    hci_transport_slip_send_frame(header, NULL, 0);
}

static void hci_transport_link_run(void){
    // exit if outgoing active
    if (uart_write_active) return;

    // process queued requests
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_SYNC){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_SYNC;
        hci_transport_link_send_sync();
        return;
    }
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_SYNC_RESPONSE){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_SYNC_RESPONSE;
        hci_transport_link_send_sync_response();
        return;
    }
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_CONFIG){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_CONFIG;
        hci_transport_link_send_config();
        return;
    }
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_CONFIG_RESPONSE){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_CONFIG_RESPONSE;
        hci_transport_link_send_config_response();
        return;
    }
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_WOKEN){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_WOKEN;
        hci_transport_link_send_woken();
        return;
    }
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_WAKEUP){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_WAKEUP;
        hci_transport_link_send_wakeup();
        return;
    }
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_QUEUED_PACKET){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_QUEUED_PACKET;
        // packet already contains ack, no need to send addtitional one
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_ACK_PACKET;
        hci_transport_link_send_queued_packet();
        return;
    }
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_ACK_PACKET){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_ACK_PACKET;
        hci_transport_link_send_ack_packet();
        return;
    }
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_SEND_SLEEP){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_SEND_SLEEP;
        hci_transport_link_actions |=  HCI_TRANSPORT_LINK_ENTER_SLEEP;
        link_peer_asleep = 1;
        hci_transport_link_send_sleep();
        return;
    }
}

static void hci_transport_link_set_timer(uint16_t timeout_ms){
    btstack_run_loop_set_timer_handler(&link_timer, &hci_transport_link_timeout_handler);
    btstack_run_loop_set_timer(&link_timer, timeout_ms);
    btstack_run_loop_add_timer(&link_timer);
}

static void hci_transport_link_timeout_handler(btstack_timer_source_t * timer){
    switch (link_state){
        case LINK_UNINITIALIZED:
            hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_SYNC;
            hci_transport_link_set_timer(LINK_PERIOD_MS);
            break;
        case LINK_INITIALIZED:
            hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_CONFIG;
            hci_transport_link_set_timer(LINK_PERIOD_MS);
            break;
        case LINK_ACTIVE:
            if (!hci_transport_link_have_outgoing_packet()){
                log_info("h5 timeout while active, but no outgoing packet");
                return;
            }
            if (link_peer_asleep){
                hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_WAKEUP;
                hci_transport_link_set_timer(LINK_WAKEUP_MS);
                return;
            }
            // resend packet
            hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_QUEUED_PACKET;
            hci_transport_link_set_timer(link_resend_timeout_ms);
            break;
        default:
            break;
    }

    hci_transport_link_run();
}

static void hci_transport_link_init(void){
    link_state = LINK_UNINITIALIZED;
    link_peer_asleep = 0;

    // get started
    hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_SYNC;
    hci_transport_link_set_timer(LINK_PERIOD_MS);
    hci_transport_link_run();
}

static int hci_transport_link_inc_seq_nr(int seq_nr){
    return (seq_nr + 1) & 0x07;
}

static int hci_transport_link_have_outgoing_packet(void){
    return hci_packet != 0;
}

static void hci_transport_link_clear_queue(void){
    btstack_run_loop_remove_timer(&link_timer);
    hci_packet = NULL;
}

static void hci_transport_h5_queue_packet(uint8_t packet_type, uint8_t *packet, int size){
    hci_packet = packet;
    hci_packet_type = packet_type;
    hci_packet_size = size;
}

static void hci_transport_h5_process_frame(uint16_t frame_size){

    if (frame_size < 4) return;

    uint8_t * slip_header  = &hci_packet_with_pre_buffer[HCI_INCOMING_PRE_BUFFER_SIZE];
    uint8_t * slip_payload = &hci_packet_with_pre_buffer[HCI_INCOMING_PRE_BUFFER_SIZE + 4];
    int       frame_size_without_header = frame_size - 4;

    int      seq_nr =  slip_header[0] & 0x07;
    int      ack_nr = (slip_header[0] >> 3)    & 0x07;
    int      data_integrity_check_present = (slip_header[0] & 0x40) != 0;
    int      reliable_packet  = (slip_header[0] & 0x80) != 0;
    uint8_t  link_packet_type = slip_header[1] & 0x0f;
    uint16_t link_payload_len = (slip_header[1] >> 4) | (slip_header[2] << 4);

    log_info("hci_transport_h5_process_frame, reliable %u, packet type %u, seq_nr %u, ack_nr %u", reliable_packet, link_packet_type, seq_nr, ack_nr);
    log_info_hexdump(slip_header, 4);
    log_info_hexdump(slip_payload, frame_size_without_header);

    // CSR 8811 does not seem to auto-detect H5 mode and sends data with even parity.
    // if this byte sequence is detected, just enable even parity
    const uint8_t sync_response_bcsp[] = {0x01, 0x7a, 0x06, 0x10};
    if (memcmp(sync_response_bcsp, slip_header, 4) == 0){
        log_info("h5: detected BSCP SYNC sent with Even Parity -> discard frame and enable Even Parity");
        btstack_uart->set_parity(1);
        return;
    }

    // validate header checksum
    uint8_t header_checksum = slip_header[0] + slip_header[1] + slip_header[2] + slip_header[3];
    if (header_checksum != 0xff){
        log_info("h5: header checksum 0x%02x (instead of 0xff)", header_checksum);
        return;
    }

    // validate payload length
    int data_integrity_len = data_integrity_check_present ? 2 : 0;
    uint16_t received_payload_len = frame_size_without_header - data_integrity_len;
    if (link_payload_len != received_payload_len){
        log_info("h5: expected payload len %u but got %u", link_payload_len, received_payload_len);
        return;
    }

    // (TODO data integrity check)

    switch (link_state){
        case LINK_UNINITIALIZED:
            if (link_packet_type != LINK_CONTROL_PACKET_TYPE) break;
            if (memcmp(slip_payload, link_control_sync, sizeof(link_control_sync)) == 0){
                log_info("link: received sync");
                hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_SYNC_RESPONSE;
            }
            if (memcmp(slip_payload, link_control_sync_response, sizeof(link_control_sync_response)) == 0){
                log_info("link: received sync response");
                link_state = LINK_INITIALIZED;
                btstack_run_loop_remove_timer(&link_timer);
                log_info("link initialized");
                //
                hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_CONFIG;
                hci_transport_link_set_timer(LINK_PERIOD_MS);
            }
            break;
        case LINK_INITIALIZED:
            if (link_packet_type != LINK_CONTROL_PACKET_TYPE) break;
            if (memcmp(slip_payload, link_control_sync, sizeof(link_control_sync)) == 0){
                log_info("link: received sync");
                hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_SYNC_RESPONSE;
            }
            if (memcmp(slip_payload, link_control_config, link_control_config_prefix_len) == 0){
                log_info("link: received config");
                hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_CONFIG_RESPONSE;
            }
            if (memcmp(slip_payload, link_control_config_response, link_control_config_response_prefix_len) == 0){
                log_info("link: received config response");
                link_state = LINK_ACTIVE;
                btstack_run_loop_remove_timer(&link_timer);
                log_info("link activated");
                //
                link_seq_nr = 0;
                link_ack_nr = 0;
                // notify upper stack that it can start
                uint8_t event[] = { HCI_EVENT_TRANSPORT_PACKET_SENT, 0};
                packet_handler(HCI_EVENT_PACKET, &event[0], sizeof(event));
            }
            break;
        case LINK_ACTIVE:

            // validate packet sequence nr in reliable packets (check for out of sequence error)
            if (reliable_packet){
                if (seq_nr != link_ack_nr){
                    log_info("expected seq nr %u, but received %u", link_ack_nr, seq_nr);
                    hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_ACK_PACKET;
                    break;
                }
                // ack packet right away
                link_ack_nr = hci_transport_link_inc_seq_nr(link_ack_nr);
                hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_ACK_PACKET;
            }

            // Process ACKs in reliable packet and explicit ack packets
            if (reliable_packet || link_packet_type == LINK_ACKNOWLEDGEMENT_TYPE){
                // our packet is good if the remote expects our seq nr + 1
                int next_seq_nr = hci_transport_link_inc_seq_nr(link_seq_nr);
                if (hci_transport_link_have_outgoing_packet() && next_seq_nr == ack_nr){
                    log_info("h5: outoing packet with seq %u ack'ed", link_seq_nr);
                    link_seq_nr = next_seq_nr;
                    hci_transport_link_clear_queue();

                    // notify upper stack that it can send again
                    uint8_t event[] = { HCI_EVENT_TRANSPORT_PACKET_SENT, 0};
                    packet_handler(HCI_EVENT_PACKET, &event[0], sizeof(event));
                }
            }

            switch (link_packet_type){
                case LINK_CONTROL_PACKET_TYPE:
                    if (memcmp(slip_payload, link_control_config, sizeof(link_control_config)) == 0){
                        log_info("link: received config");
                        hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_CONFIG_RESPONSE;
                        break;
                    }
                    if (memcmp(slip_payload, link_control_sync, sizeof(link_control_sync)) == 0){
                        log_info("link: received sync in ACTIVE STATE!");
                        // TODO sync during active indicates peer reset -> full upper layer reset necessary
                        break;
                    }
                    if (memcmp(slip_payload, link_control_sleep, sizeof(link_control_sleep)) == 0){
                        if (btstack_uart_sleep_mode){
                            log_info("link: received sleep message. Enabling UART Sleep.");
                            btstack_uart->set_sleep(btstack_uart_sleep_mode);
                        } else {
                            log_info("link: received sleep message. UART Sleep not supported");
                        }
                        link_peer_asleep = 1;
                        break;
                    }
                    if (memcmp(slip_payload, link_control_wakeup, sizeof(link_control_wakeup)) == 0){
                        log_info("link: received wakupe message -> send woken");
                        link_peer_asleep = 0;
                        hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_WOKEN;
                        break;
                    }
                    if (memcmp(slip_payload, link_control_woken, sizeof(link_control_woken)) == 0){
                        log_info("link: received woken message");
                        link_peer_asleep = 0;
                        // queued packet will be sent in hci_transport_link_run if needed
                        break;
                    }
                    break;
                case HCI_EVENT_PACKET:
                case HCI_ACL_DATA_PACKET:
                case HCI_SCO_DATA_PACKET:
                    // seems like peer is awake
                    link_peer_asleep = 0;
                    // forward packet to stack
                    packet_handler(link_packet_type, slip_payload, link_payload_len);
                    // reset inactvitiy timer
                    hci_transport_inactivity_timer_set();
                    break;
            }

            break;
        default:
            break;
    }

    hci_transport_link_run();
}

// recommendet time until resend: 3 * time of largest packet
static uint16_t hci_transport_link_calc_resend_timeout(uint32_t baudrate){
    uint32_t max_packet_size_in_bit = (HCI_PACKET_BUFFER_SIZE + 6) << 3;
    uint32_t t_max_x3_ms = max_packet_size_in_bit * 3000 / baudrate;
    log_info("resend timeout for %u baud: %u ms", baudrate, t_max_x3_ms);
    return t_max_x3_ms;
}

static void hci_transport_link_update_resend_timeout(uint32_t baudrate){
    link_resend_timeout_ms = hci_transport_link_calc_resend_timeout(baudrate);
}

/// H5 Interface

static uint8_t hci_transport_link_read_byte;

static void hci_transport_h5_read_next_byte(void){
    log_debug("h5: rx nxt");
    btstack_uart->receive_block(&hci_transport_link_read_byte, 1);
}

static void hci_transport_h5_block_received(){
    log_debug("slip: process 0x%02x", hci_transport_link_read_byte);
    btstack_slip_decoder_process(hci_transport_link_read_byte);
    uint16_t frame_size = btstack_slip_decoder_frame_size();
    if (frame_size) {
        hci_transport_h5_process_frame(frame_size);
        hci_transport_slip_init();
    }
    hci_transport_h5_read_next_byte();
}

static void hci_transport_h5_block_sent(void){
    uart_write_active = 0;

    // enter sleep mode after sending sleep message
    if (hci_transport_link_actions & HCI_TRANSPORT_LINK_ENTER_SLEEP){
        hci_transport_link_actions &= ~HCI_TRANSPORT_LINK_ENTER_SLEEP;
        if (btstack_uart_sleep_mode){
            log_info("link: sent sleep message. Enabling UART Sleep.");
            btstack_uart->set_sleep(btstack_uart_sleep_mode);
        } else {
            log_info("link: sent sleep message. UART Sleep not supported");
        }
    }

    hci_transport_link_run();
}

static void hci_transport_h5_init(const void * transport_config){
    // check for hci_transport_config_uart_t
    if (!transport_config) {
        log_error("hci_transport_h5: no config!");
        return;
    }
    if (((hci_transport_config_t*)transport_config)->type != HCI_TRANSPORT_CONFIG_UART) {
        log_error("hci_transport_h5: config not of type != HCI_TRANSPORT_CONFIG_UART!");
        return;
    }

    // extract UART config from transport config
    hci_transport_config_uart_t * hci_transport_config_uart = (hci_transport_config_uart_t*) transport_config;
    uart_config.baudrate    = hci_transport_config_uart->baudrate_init;
    uart_config.flowcontrol = hci_transport_config_uart->flowcontrol;
    uart_config.device_name = hci_transport_config_uart->device_name;

    // setup UART driver
    btstack_uart->init(&uart_config);
    btstack_uart->set_block_received(&hci_transport_h5_block_received);
    btstack_uart->set_block_sent(&hci_transport_h5_block_sent);
}

static int hci_transport_h5_open(void){
    int res = btstack_uart->open();
    if (res){
        return res;
    }

    // check if wake on RX can be used
    btstack_uart_sleep_mode = BTSTACK_UART_SLEEP_OFF;
    int supported_sleep_modes = 0;
    if (btstack_uart->get_supported_sleep_modes){
        supported_sleep_modes = btstack_uart->get_supported_sleep_modes();
    }
    if (supported_sleep_modes & BTSTACK_UART_SLEEP_MASK_RTS_LOW_WAKE_ON_RX_EDGE){
        log_info("H5: using wake on RX");
        btstack_uart_sleep_mode = BTSTACK_UART_SLEEP_RTS_LOW_WAKE_ON_RX_EDGE;
    } else {
        log_info("H5: UART driver does not provide compatible sleep mode");
    }

    // setup resend timeout
    hci_transport_link_update_resend_timeout(uart_config.baudrate);

    // init slip parser state machine
    hci_transport_slip_init();

    // init link management - already starts syncing
    hci_transport_link_init();

    // start receiving
    hci_transport_h5_read_next_byte();

    return 0;
}

static int hci_transport_h5_close(void){
    return btstack_uart->close();
    return 0;
}

static void hci_transport_h5_register_packet_handler(void (*handler)(uint8_t packet_type, uint8_t *packet, uint16_t size)){
    packet_handler = handler;
}

static int hci_transport_h5_can_send_packet_now(uint8_t packet_type){
    int res = !hci_transport_link_have_outgoing_packet() && link_state == LINK_ACTIVE;
    log_info("hci_transport_h5_can_send_packet_now: %u", res);
    return res;
}

static int hci_transport_h5_send_packet(uint8_t packet_type, uint8_t *packet, int size){
    if (!hci_transport_h5_can_send_packet_now(packet_type)){
        log_error("hci_transport_h5_send_packet called but in state %u", link_state);
        return -1;
    }

    // store request
    hci_transport_h5_queue_packet(packet_type, packet, size);

    // send wakeup first
    if (link_peer_asleep){
        if (btstack_uart_sleep_mode){
            log_info("h5: disable UART sleep");
            btstack_uart->set_sleep(BTSTACK_UART_SLEEP_OFF);
        }
        hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_WAKEUP;
        hci_transport_link_set_timer(LINK_WAKEUP_MS);
    } else {
        hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_QUEUED_PACKET;
        hci_transport_link_set_timer(link_resend_timeout_ms);
    }
    hci_transport_link_run();
    return 0;
}

static int hci_transport_h5_set_baudrate(uint32_t baudrate){

    log_info("hci_transport_h5_set_baudrate %u", baudrate);
    int res = btstack_uart->set_baudrate(baudrate);

    if (res) return res;
    hci_transport_link_update_resend_timeout(baudrate);
    return 0;
}

static void hci_transport_h5_reset_link(void){

    log_info("hci_transport_h5_reset_link");

    // clear outgoing queue
    hci_transport_link_clear_queue();

    // init slip parser state machine
    hci_transport_slip_init();

    // init link management - already starts syncing
    hci_transport_link_init();
}

static const hci_transport_t hci_transport_h5 = {
    /* const char * name; */                                        "H5",
    /* void   (*init) (const void *transport_config); */            &hci_transport_h5_init,
    /* int    (*open)(void); */                                     &hci_transport_h5_open,
    /* int    (*close)(void); */                                    &hci_transport_h5_close,
    /* void   (*register_packet_handler)(void (*handler)(...); */   &hci_transport_h5_register_packet_handler,
    /* int    (*can_send_packet_now)(uint8_t packet_type); */       &hci_transport_h5_can_send_packet_now,
    /* int    (*send_packet)(...); */                               &hci_transport_h5_send_packet,
    /* int    (*set_baudrate)(uint32_t baudrate); */                &hci_transport_h5_set_baudrate,
    /* void   (*reset_link)(void); */                               &hci_transport_h5_reset_link,
};

// configure and return h5 singleton
const hci_transport_t * hci_transport_h5_instance(const btstack_uart_block_t * uart_driver) {
    btstack_uart = uart_driver;
    return &hci_transport_h5;
}

void hci_transport_h5_set_auto_sleep(uint16_t inactivity_timeout_ms){
    link_inactivity_timeout_ms = inactivity_timeout_ms;
}