xref: /btstack/src/classic/avrcp_controller.c (revision adaba9f34040c696f6e8e6f1096f218bf6ceb78e)

/*
 * 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
 * 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]
 *
 */

#define __BTSTACK_FILE__ "avrcp_controller.c"

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <inttypes.h>

#include "btstack.h"
#include "classic/avrcp.h"
#include "classic/avrcp_controller.h"

static avrcp_context_t avrcp_controller_context;

void avrcp_controller_create_sdp_record(uint8_t * service, uint32_t service_record_handle, uint8_t browsing, uint16_t supported_features, const char * service_name, const char * service_provider_name){
    avrcp_create_sdp_record(1, service, service_record_handle, browsing, supported_features, service_name, service_provider_name);
}

static void avrcp_emit_repeat_and_shuffle_mode(btstack_packet_handler_t callback, uint16_t avrcp_cid, uint8_t ctype, avrcp_repeat_mode_t repeat_mode, avrcp_shuffle_mode_t shuffle_mode){
    if (!callback) return;
    uint8_t event[8];
    int pos = 0;
    event[pos++] = HCI_EVENT_AVRCP_META;
    event[pos++] = sizeof(event) - 2;
    event[pos++] = AVRCP_SUBEVENT_SHUFFLE_AND_REPEAT_MODE;
    little_endian_store_16(event, pos, avrcp_cid);
    pos += 2;
    event[pos++] = ctype;
    event[pos++] = repeat_mode;
    event[pos++] = shuffle_mode;
    (*callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
}

static void avrcp_emit_operation_status(btstack_packet_handler_t callback, uint8_t subevent, uint16_t avrcp_cid, uint8_t ctype, uint8_t operation_id){
    if (!callback) return;
    uint8_t event[7];
    int pos = 0;
    event[pos++] = HCI_EVENT_AVRCP_META;
    event[pos++] = sizeof(event) - 2;
    event[pos++] = subevent;
    little_endian_store_16(event, pos, avrcp_cid);
    pos += 2;
    event[pos++] = ctype;
    event[pos++] = operation_id;
    (*callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
}

static void avrcp_press_and_hold_timeout_handler(btstack_timer_source_t * timer){
    UNUSED(timer);
    avrcp_connection_t * connection = btstack_run_loop_get_timer_context(timer);
    btstack_run_loop_set_timer(&connection->press_and_hold_cmd_timer, 2000); // 2 seconds timeout
    btstack_run_loop_add_timer(&connection->press_and_hold_cmd_timer);
    connection->state = AVCTP_W2_SEND_PRESS_COMMAND;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
}

static void avrcp_press_and_hold_timer_start(avrcp_connection_t * connection){
    btstack_run_loop_remove_timer(&connection->press_and_hold_cmd_timer);
    btstack_run_loop_set_timer_handler(&connection->press_and_hold_cmd_timer, avrcp_press_and_hold_timeout_handler);
    btstack_run_loop_set_timer_context(&connection->press_and_hold_cmd_timer, connection);
    btstack_run_loop_set_timer(&connection->press_and_hold_cmd_timer, 2000); // 2 seconds timeout
    btstack_run_loop_add_timer(&connection->press_and_hold_cmd_timer);
}

static void avrcp_press_and_hold_timer_stop(avrcp_connection_t * connection){
    connection->continuous_fast_forward_cmd = 0;
    btstack_run_loop_remove_timer(&connection->press_and_hold_cmd_timer);
}

static uint8_t request_pass_through_release_control_cmd(avrcp_connection_t * connection){
    connection->state = AVCTP_W2_SEND_RELEASE_COMMAND;
    if (connection->continuous_fast_forward_cmd){
        avrcp_press_and_hold_timer_stop(connection);
    }
    connection->cmd_operands[0] = 0x80 | connection->cmd_operands[0];
    connection->transaction_label++;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

static inline uint8_t request_pass_through_press_control_cmd(uint16_t avrcp_cid, avrcp_operation_id_t opid, uint16_t playback_speed, uint8_t continuous_fast_forward_cmd, avrcp_context_t * context){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, context);
    if (!connection){
        log_error("avrcp: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    connection->state = AVCTP_W2_SEND_PRESS_COMMAND;
    connection->command_opcode =  AVRCP_CMD_OPCODE_PASS_THROUGH;
    connection->command_type = AVRCP_CTYPE_CONTROL;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_PANEL;
    connection->subunit_id =   AVRCP_SUBUNIT_ID;
    connection->cmd_operands_length = 0;

    connection->continuous_fast_forward_cmd = continuous_fast_forward_cmd;
    connection->cmd_operands_length = 2;
    connection->cmd_operands[0] = opid;
    if (playback_speed > 0){
        connection->cmd_operands[2] = playback_speed;
        connection->cmd_operands_length++;
    }
    connection->cmd_operands[1] = connection->cmd_operands_length - 2;

    if (connection->continuous_fast_forward_cmd){
        avrcp_press_and_hold_timer_start(connection);
    }

    connection->transaction_label++;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

static uint8_t request_single_pass_through_press_control_cmd(uint16_t avrcp_cid, avrcp_operation_id_t opid, uint16_t playback_speed){
    return request_pass_through_press_control_cmd(avrcp_cid, opid, playback_speed, 0, &avrcp_controller_context);
}

static uint8_t request_continuous_pass_through_press_control_cmd(uint16_t avrcp_cid, avrcp_operation_id_t opid, uint16_t playback_speed){
    return request_pass_through_press_control_cmd(avrcp_cid, opid, playback_speed, 1, &avrcp_controller_context);
}

static int avrcp_send_cmd(uint16_t cid, avrcp_connection_t * connection){
    uint8_t command[30];
    int pos = 0;
    // transport header
    // Transaction label | Packet_type | C/R | IPID (1 == invalid profile identifier)
    command[pos++] = (connection->transaction_label << 4) | (AVRCP_SINGLE_PACKET << 2) | (AVRCP_COMMAND_FRAME << 1) | 0;
    // Profile IDentifier (PID)
    command[pos++] = BLUETOOTH_SERVICE_CLASS_AV_REMOTE_CONTROL >> 8;
    command[pos++] = BLUETOOTH_SERVICE_CLASS_AV_REMOTE_CONTROL & 0x00FF;

    // command_type
    command[pos++] = connection->command_type;
    // subunit_type | subunit ID
    command[pos++] = (connection->subunit_type << 3) | connection->subunit_id;
    // opcode
    command[pos++] = (uint8_t)connection->command_opcode;
    // operands
    memcpy(command+pos, connection->cmd_operands, connection->cmd_operands_length);
    pos += connection->cmd_operands_length;

    return l2cap_send(cid, command, pos);
}

static int avrcp_register_notification(avrcp_connection_t * connection, avrcp_notification_event_id_t event_id){
    if (connection->notifications_to_deregister & (1 << event_id)) return 0;
    if (connection->notifications_enabled & (1 << event_id)) return 0;
    if (connection->notifications_to_register & (1 << event_id)) return 0;
    connection->notifications_to_register |= (1 << event_id);
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return 1;
}

static void avrcp_prepare_notification(avrcp_connection_t * connection, avrcp_notification_event_id_t event_id){
    connection->transaction_label++;
    connection->command_opcode = AVRCP_CMD_OPCODE_VENDOR_DEPENDENT;
    connection->command_type = AVRCP_CTYPE_NOTIFY;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_PANEL;
    connection->subunit_id = AVRCP_SUBUNIT_ID;
    int pos = 0;
    big_endian_store_24(connection->cmd_operands, pos, BT_SIG_COMPANY_ID);
    pos += 3;
    connection->cmd_operands[pos++] = AVRCP_PDU_ID_REGISTER_NOTIFICATION;
    connection->cmd_operands[pos++] = 0;                     // reserved(upper 6) | packet_type -> 0
    big_endian_store_16(connection->cmd_operands, pos, 5);     // parameter length
    pos += 2;
    connection->cmd_operands[pos++] = event_id;
    big_endian_store_32(connection->cmd_operands, pos, 0);
    pos += 4;
    connection->cmd_operands_length = pos;
    // AVRCP_SPEC_V14.pdf 166
    // answer page 61
}

static void avrcp_handle_l2cap_data_packet_for_signaling_connection(avrcp_connection_t * connection, uint8_t *packet, uint16_t size){
    uint8_t operands[20];
    uint8_t opcode;
    int     pos = 3;
    // uint8_t transport_header = packet[0];
    // uint8_t transaction_label = transport_header >> 4;
    // uint8_t packet_type = (transport_header & 0x0F) >> 2;
    // uint8_t frame_type = (transport_header & 0x03) >> 1;
    // uint8_t ipid = transport_header & 0x01;
    // uint8_t byte_value = packet[2];
    // uint16_t pid = (byte_value << 8) | packet[2];

    avrcp_command_type_t ctype = (avrcp_command_type_t) packet[pos++];
    uint8_t byte_value = packet[pos++];
    avrcp_subunit_type_t subunit_type = (avrcp_subunit_type_t) (byte_value >> 3);
    avrcp_subunit_type_t subunit_id = (avrcp_subunit_type_t)   (byte_value & 0x07);
    opcode = packet[pos++];

    // printf("    Transport header 0x%02x (transaction_label %d, packet_type %d, frame_type %d, ipid %d), pid 0x%4x\n",
    //     transport_header, transaction_label, packet_type, frame_type, ipid, pid);
    // // printf_hexdump(packet+pos, size-pos);

    uint8_t pdu_id;
    uint16_t param_length;
    switch (avrcp_cmd_opcode(packet,size)){
        case AVRCP_CMD_OPCODE_UNIT_INFO:{
            if (connection->state != AVCTP_W2_RECEIVE_RESPONSE) return;
            connection->state = AVCTP_CONNECTION_OPENED;

            // operands:
            memcpy(operands, packet+pos, 5);
            uint8_t unit_type = operands[1] >> 3;
            uint8_t unit = operands[1] & 0x07;
            uint32_t company_id = operands[2] << 16 | operands[3] << 8 | operands[4];
            log_info("    UNIT INFO response: ctype 0x%02x (0C), subunit_type 0x%02x (1F), subunit_id 0x%02x (07), opcode 0x%02x (30), unit_type 0x%02x, unit %d, company_id 0x%06" PRIx32,
                ctype, subunit_type, subunit_id, opcode, unit_type, unit, company_id );
            break;
        }
        case AVRCP_CMD_OPCODE_VENDOR_DEPENDENT:
            if (size - pos < 7) {
                log_error("avrcp: wrong packet size");
                return;
            };
            // operands:
            memcpy(operands, packet+pos, 7);
            pos += 7;
            // uint32_t company_id = operands[0] << 16 | operands[1] << 8 | operands[2];
            pdu_id = operands[3];

            if (connection->state != AVCTP_W2_RECEIVE_RESPONSE && pdu_id != AVRCP_PDU_ID_REGISTER_NOTIFICATION){
                log_info("AVRCP_CMD_OPCODE_VENDOR_DEPENDENT state %d", connection->state);
                return;
            }
            connection->state = AVCTP_CONNECTION_OPENED;


            // uint8_t unit_type = operands[4] >> 3;
            // uint8_t unit = operands[4] & 0x07;
            param_length = big_endian_read_16(operands, 5);

            // printf("    VENDOR DEPENDENT response: ctype 0x%02x (0C), subunit_type 0x%02x (1F), subunit_id 0x%02x (07), opcode 0x%02x (30), unit_type 0x%02x, unit %d, company_id 0x%06x\n",
            //     ctype, subunit_type, subunit_id, opcode, unit_type, unit, company_id );

            // if (ctype == AVRCP_CTYPE_RESPONSE_INTERIM) return;
            log_info("        VENDOR DEPENDENT response: pdu id 0x%02x, param_length %d, status %s", pdu_id, param_length, avrcp_ctype2str(ctype));
            switch (pdu_id){
                case AVRCP_PDU_ID_GetCurrentPlayerApplicationSettingValue:{
                    uint8_t num_attributes = packet[pos++];
                    int i;
                    avrcp_repeat_mode_t  repeat_mode =  AVRCP_REPEAT_MODE_INVALID;
                    avrcp_shuffle_mode_t shuffle_mode = AVRCP_SHUFFLE_MODE_INVALID;
                    for (i = 0; i < num_attributes; i++){
                        uint8_t attribute_id    = packet[pos++];
                        uint8_t value = packet[pos++];
                        switch (attribute_id){
                            case 0x02:
                                repeat_mode = (avrcp_repeat_mode_t) value;
                                break;
                            case 0x03:
                                shuffle_mode = (avrcp_shuffle_mode_t) value;
                                break;
                            default:
                                break;
                        }
                    }
                    avrcp_emit_repeat_and_shuffle_mode(avrcp_controller_context.avrcp_callback, connection->avrcp_cid, ctype, repeat_mode, shuffle_mode);
                    break;
                }
                case AVRCP_PDU_ID_SetPlayerApplicationSettingValue:{
                    uint8_t event[6];
                    int offset = 0;
                    event[offset++] = HCI_EVENT_AVRCP_META;
                    event[offset++] = sizeof(event) - 2;
                    event[offset++] = AVRCP_SUBEVENT_PLAYER_APPLICATION_VALUE_RESPONSE;
                    little_endian_store_16(event, offset, connection->avrcp_cid);
                    offset += 2;
                    event[offset++] = ctype;
                    (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
                    break;
                }
                case AVRCP_PDU_ID_SET_ABSOLUTE_VOLUME:{
                    uint8_t event[7];
                    int offset = 0;
                    event[offset++] = HCI_EVENT_AVRCP_META;
                    event[offset++] = sizeof(event) - 2;
                    event[offset++] = AVRCP_SUBEVENT_SET_ABSOLUTE_VOLUME_RESPONSE;
                    little_endian_store_16(event, offset, connection->avrcp_cid);
                    offset += 2;
                    event[offset++] = ctype;
                    event[offset++] = packet[pos++];
                    (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
                    break;
                }
                case AVRCP_PDU_ID_GET_CAPABILITIES:{
                    avrcp_capability_id_t capability_id = (avrcp_capability_id_t) packet[pos++];
                    uint8_t capability_count = packet[pos++];
                    int i;
                    switch (capability_id){
                        case AVRCP_CAPABILITY_ID_COMPANY:
                            // log_info("Supported companies %d: ", capability_count);
                            for (i = 0; i < capability_count; i++){
                                uint32_t company_id = big_endian_read_24(packet, pos);
                                pos += 3;
                                log_info("  0x%06" PRIx32 ", ", company_id);
                            }
                            break;
                        case AVRCP_CAPABILITY_ID_EVENT:
                            // log_info("Supported events %d: ", capability_count);
                            for (i = 0; i < capability_count; i++){
                                uint8_t event_id = packet[pos++];
                                log_info("  0x%02x %s", event_id, avrcp_event2str(event_id));
                            }
                            break;
                    }
                    break;
                }
                case AVRCP_PDU_ID_GET_PLAY_STATUS:{
                    uint32_t song_length = big_endian_read_32(packet, pos);
                    pos += 4;
                    uint32_t song_position = big_endian_read_32(packet, pos);
                    pos += 4;
                    uint8_t play_status = packet[pos];
                    // log_info("        GET_PLAY_STATUS length 0x%04X, position 0x%04X, status %s", song_length, song_position, avrcp_play_status2str(play_status));

                    uint8_t event[15];
                    int offset = 0;
                    event[offset++] = HCI_EVENT_AVRCP_META;
                    event[offset++] = sizeof(event) - 2;
                    event[offset++] = AVRCP_SUBEVENT_PLAY_STATUS;
                    little_endian_store_16(event, offset, connection->avrcp_cid);
                    offset += 2;
                    event[offset++] = ctype;
                    little_endian_store_32(event, offset, song_length);
                    offset += 4;
                    little_endian_store_32(event, offset, song_position);
                    offset += 4;
                    event[offset++] = play_status;
                    (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
                    break;
                }
                case AVRCP_PDU_ID_REGISTER_NOTIFICATION:{
                    avrcp_notification_event_id_t  event_id = (avrcp_notification_event_id_t) packet[pos++];
                    uint16_t event_mask = (1 << event_id);
                    uint16_t reset_event_mask = ~event_mask;
                    switch (ctype){
                        case AVRCP_CTYPE_RESPONSE_INTERIM:
                            // register as enabled
                            connection->notifications_enabled |= event_mask;
                            // printf("INTERIM notifications_enabled 0x%2x, notifications_to_register 0x%2x\n", connection->notifications_enabled,  connection->notifications_to_register);
                            break;
                        case AVRCP_CTYPE_RESPONSE_CHANGED_STABLE:
                            // received change, event is considered deregistered
                            // we are re-enabling it automatically, if it is not
                            // explicitly disabled
                            connection->notifications_enabled &= reset_event_mask;
                            if (! (connection->notifications_to_deregister & event_mask)){
                                avrcp_register_notification(connection, event_id);
                                // printf("CHANGED_STABLE notifications_enabled 0x%2x, notifications_to_register 0x%2x\n", connection->notifications_enabled,  connection->notifications_to_register);
                            } else {
                                connection->notifications_to_deregister &= reset_event_mask;
                            }
                            break;
                        default:
                            connection->notifications_to_register &= reset_event_mask;
                            connection->notifications_enabled &= reset_event_mask;
                            connection->notifications_to_deregister &= reset_event_mask;
                            break;
                    }

                    switch (event_id){
                        case AVRCP_NOTIFICATION_EVENT_PLAYBACK_STATUS_CHANGED:{
                            uint8_t event[7];
                            int offset = 0;
                            event[offset++] = HCI_EVENT_AVRCP_META;
                            event[offset++] = sizeof(event) - 2;
                            event[offset++] = AVRCP_SUBEVENT_NOTIFICATION_PLAYBACK_STATUS_CHANGED;
                            little_endian_store_16(event, offset, connection->avrcp_cid);
                            offset += 2;
                            event[offset++] = ctype;
                            event[offset++] = packet[pos];
                            (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
                            break;
                        }
                        case AVRCP_NOTIFICATION_EVENT_TRACK_CHANGED:{
                            uint8_t event[6];
                            int offset = 0;
                            event[offset++] = HCI_EVENT_AVRCP_META;
                            event[offset++] = sizeof(event) - 2;
                            event[offset++] = AVRCP_SUBEVENT_NOTIFICATION_TRACK_CHANGED;
                            little_endian_store_16(event, offset, connection->avrcp_cid);
                            offset += 2;
                            event[offset++] = ctype;
                            (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
                            break;
                        }
                        case AVRCP_NOTIFICATION_EVENT_NOW_PLAYING_CONTENT_CHANGED:{
                            uint8_t event[6];
                            int offset = 0;
                            event[offset++] = HCI_EVENT_AVRCP_META;
                            event[offset++] = sizeof(event) - 2;
                            event[offset++] = AVRCP_SUBEVENT_NOTIFICATION_NOW_PLAYING_CONTENT_CHANGED;
                            little_endian_store_16(event, offset, connection->avrcp_cid);
                            offset += 2;
                            event[offset++] = ctype;
                            (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
                            break;
                        }
                        case AVRCP_NOTIFICATION_EVENT_AVAILABLE_PLAYERS_CHANGED:{
                            uint8_t event[6];
                            int offset = 0;
                            event[offset++] = HCI_EVENT_AVRCP_META;
                            event[offset++] = sizeof(event) - 2;
                            event[offset++] = AVRCP_SUBEVENT_NOTIFICATION_AVAILABLE_PLAYERS_CHANGED;
                            little_endian_store_16(event, offset, connection->avrcp_cid);
                            offset += 2;
                            event[offset++] = ctype;
                            (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
                            break;
                        }
                        case AVRCP_NOTIFICATION_EVENT_VOLUME_CHANGED:{
                            uint8_t event[7];
                            int offset = 0;
                            event[offset++] = HCI_EVENT_AVRCP_META;
                            event[offset++] = sizeof(event) - 2;
                            event[offset++] = AVRCP_SUBEVENT_NOTIFICATION_VOLUME_CHANGED;
                            little_endian_store_16(event, offset, connection->avrcp_cid);
                            offset += 2;
                            event[offset++] = ctype;
                            event[offset++] = packet[pos++] & 0x7F;
                            (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, sizeof(event));
                            break;
                        }
                        // case AVRCP_NOTIFICATION_EVENT_PLAYER_APPLICATION_SETTING_CHANGED:{
                        //     uint8_t num_PlayerApplicationSettingAttributes = packet[pos++];
                        //     int i;
                        //     for (i = 0; i < num_PlayerApplicationSettingAttributes; i++){
                        //         uint8_t PlayerApplicationSetting_AttributeID = packet[pos++];
                        //         uint8_t PlayerApplicationSettingValueID = packet[pos++];
                        //     }
                        //     break;
                        // }
                        // case AVRCP_NOTIFICATION_EVENT_ADDRESSED_PLAYER_CHANGED:
                        //     uint16_t player_id = big_endian_read_16(packet, pos);
                        //     pos += 2;
                        //     uint16_t uid_counter = big_endian_read_16(packet, pos);
                        //     pos += 2;
                        //     break;
                        // case AVRCP_NOTIFICATION_EVENT_UIDS_CHANGED:
                        //     uint16_t uid_counter = big_endian_read_16(packet, pos);
                        //     pos += 2;
                        //     break;
                        default:
                            log_info("avrcp: not implemented");
                            break;
                    }
                    if (connection->notifications_to_register != 0){
                        avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
                    }
                    break;
                }

                case AVRCP_PDU_ID_GET_ELEMENT_ATTRIBUTES:{
                    uint8_t num_attributes = packet[pos++];
                    unsigned int i;
                    struct item {
                        uint16_t len;
                        uint8_t  * value;
                    } items[AVRCP_MEDIA_ATTR_COUNT];
                    memset(items, 0, sizeof(items));

                    uint16_t string_attributes_len = 0;
                    uint8_t  num_string_attributes = 0;
                    uint16_t total_event_payload_for_string_attributes = HCI_EVENT_PAYLOAD_SIZE-2;
                    uint16_t max_string_attribute_value_len = 0;
                    if (ctype == AVRCP_CTYPE_RESPONSE_IMPLEMENTED_STABLE || ctype == AVRCP_CTYPE_RESPONSE_CHANGED_STABLE){
                        for (i = 0; i < num_attributes; i++){
                            // use local variables to avoid compiler warning
                            uint32_t avrcp_media_attribute_id =  big_endian_read_32(packet, pos);
                            avrcp_media_attribute_id_t attr_id = (avrcp_media_attribute_id_t) avrcp_media_attribute_id;
                            pos += 4;
                            // uint16_t character_set = big_endian_read_16(packet, pos);
                            pos += 2;
                            uint16_t attr_value_length = big_endian_read_16(packet, pos);
                            pos += 2;

                            // debug - to remove later
                            uint8_t  value[100];
                            uint16_t value_len = sizeof(value) <= attr_value_length? sizeof(value) - 1 : attr_value_length;
                            memcpy(value, packet+pos, value_len);
                            value[value_len] = 0;
                            // printf("Now Playing Info %s: %s \n", attribute2str(attr_id), value);
                            // end debug

                            if ((attr_id >= 1) || (attr_id <= AVRCP_MEDIA_ATTR_COUNT)) {
                                items[attr_id-1].len = attr_value_length;
                                items[attr_id-1].value = &packet[pos];
                                switch (attr_id){
                                    case AVRCP_MEDIA_ATTR_TITLE:
                                    case AVRCP_MEDIA_ATTR_ARTIST:
                                    case AVRCP_MEDIA_ATTR_ALBUM:
                                    case AVRCP_MEDIA_ATTR_GENRE:
                                        num_string_attributes++;
                                        string_attributes_len += attr_value_length;
                                        if (max_string_attribute_value_len < attr_value_length){
                                            max_string_attribute_value_len = attr_value_length;
                                        }
                                        break;
                                    default:
                                        break;
                                }
                            }
                            pos += attr_value_length;
                        }
                    }

                    // subtract space for fixed fields
                    total_event_payload_for_string_attributes -= 14 + 4;    // 4 for '\0'

                    // @TODO optimize space by repeatedly decreasing max_string_attribute_value_len until it fits into buffer instead of crude divion
                    uint16_t max_value_len = total_event_payload_for_string_attributes > string_attributes_len? max_string_attribute_value_len : total_event_payload_for_string_attributes/(string_attributes_len+1) - 1;
                    // printf("num_string_attributes %d, string_attributes_len %d, total_event_payload_for_string_attributes %d, max_value_len %d \n", num_string_attributes, string_attributes_len, total_event_payload_for_string_attributes, max_value_len);

                    const uint8_t attribute_order[] = {
                        AVRCP_MEDIA_ATTR_TRACK,
                        AVRCP_MEDIA_ATTR_TOTAL_TRACKS,
                        AVRCP_MEDIA_ATTR_SONG_LENGTH,
                        AVRCP_MEDIA_ATTR_TITLE,
                        AVRCP_MEDIA_ATTR_ARTIST,
                        AVRCP_MEDIA_ATTR_ALBUM,
                        AVRCP_MEDIA_ATTR_GENRE
                    };

                    uint8_t event[HCI_EVENT_BUFFER_SIZE];
                    event[0] = HCI_EVENT_AVRCP_META;
                    pos = 2;
                    event[pos++] = AVRCP_SUBEVENT_NOW_PLAYING_INFO;
                    little_endian_store_16(event, pos, connection->avrcp_cid);
                    pos += 2;
                    event[pos++] = ctype;
                    for (i = 0; i < sizeof(attribute_order); i++){
                        avrcp_media_attribute_id_t attr_id = (avrcp_media_attribute_id_t) attribute_order[i];
                        uint16_t value_len = 0;
                        switch (attr_id){
                            case AVRCP_MEDIA_ATTR_TITLE:
                            case AVRCP_MEDIA_ATTR_ARTIST:
                            case AVRCP_MEDIA_ATTR_ALBUM:
                            case AVRCP_MEDIA_ATTR_GENRE:
                                if (items[attr_id-1].value){
                                    value_len = items[attr_id-1].len <= max_value_len ? items[attr_id-1].len : max_value_len;
                                }
                                event[pos++] = value_len + 1;
                                if (value_len){
                                    memcpy(event+pos, items[attr_id-1].value, value_len);
                                    pos += value_len;
                                }
                                event[pos++] = 0;
                                break;
                            case AVRCP_MEDIA_ATTR_SONG_LENGTH:
                                if (items[attr_id-1].value){
                                    little_endian_store_32(event, pos, btstack_atoi((char *)items[attr_id-1].value));
                                } else {
                                    little_endian_store_32(event, pos, 0);
                                }
                                pos += 4;
                                break;
                            case AVRCP_MEDIA_ATTR_TRACK:
                            case AVRCP_MEDIA_ATTR_TOTAL_TRACKS:
                                if (items[attr_id-1].value){
                                    event[pos++] = btstack_atoi((char *)items[attr_id-1].value);
                                } else {
                                    event[pos++] = 0;
                                }
                                break;
                        }
                    }
                    event[1] = pos - 2;
                    // printf_hexdump(event, pos);
                    (*avrcp_controller_context.avrcp_callback)(HCI_EVENT_PACKET, 0, event, pos);
                    break;
                }
                default:
                    break;
            }
            break;
        case AVRCP_CMD_OPCODE_PASS_THROUGH:{
            // 0x80 | connection->cmd_operands[0]
            uint8_t operation_id = packet[pos++];
            switch (connection->state){
                case AVCTP_W2_RECEIVE_PRESS_RESPONSE:
                    if (connection->continuous_fast_forward_cmd){
                        connection->state = AVCTP_W4_STOP;
                    } else {
                        connection->state = AVCTP_W2_SEND_RELEASE_COMMAND;
                    }
                    break;
                case AVCTP_W2_RECEIVE_RESPONSE:
                    connection->state = AVCTP_CONNECTION_OPENED;
                    break;
                default:
                    // check for notifications? move state transition down
                    // log_info("AVRCP_CMD_OPCODE_PASS_THROUGH state %d\n", connection->state);
                    break;
            }
            if (connection->state == AVCTP_W4_STOP){
                avrcp_emit_operation_status(avrcp_controller_context.avrcp_callback, AVRCP_SUBEVENT_OPERATION_START, connection->avrcp_cid, ctype, operation_id);
            }
            if (connection->state == AVCTP_CONNECTION_OPENED) {
                // RELEASE response
                operation_id = operation_id & 0x7F;
                avrcp_emit_operation_status(avrcp_controller_context.avrcp_callback, AVRCP_SUBEVENT_OPERATION_COMPLETE, connection->avrcp_cid, ctype, operation_id);
            }
            if (connection->state == AVCTP_W2_SEND_RELEASE_COMMAND){
                // PRESS response
                request_pass_through_release_control_cmd(connection);
            }
            break;
        }
        default:
            break;
    }
}

static void avrcp_controller_handle_can_send_now(avrcp_connection_t * connection){
    int i;
    switch (connection->state){
        case AVCTP_W2_SEND_PRESS_COMMAND:
            connection->state = AVCTP_W2_RECEIVE_PRESS_RESPONSE;
            avrcp_send_cmd(connection->l2cap_signaling_cid, connection);
            break;
        case AVCTP_W2_SEND_COMMAND:
        case AVCTP_W2_SEND_RELEASE_COMMAND:
            connection->state = AVCTP_W2_RECEIVE_RESPONSE;
            avrcp_send_cmd(connection->l2cap_signaling_cid, connection);
            break;
        case AVCTP_CONNECTION_OPENED:
            if (connection->notifications_to_register != 0){
                for (i = 1; i <= AVRCP_NOTIFICATION_EVENT_VOLUME_CHANGED; i++){
                    if (connection->notifications_to_register & (1<<i)){
                        connection->notifications_to_register &= ~ (1 << i);
                        avrcp_prepare_notification(connection, (avrcp_notification_event_id_t) i);
                        connection->state = AVCTP_W2_RECEIVE_RESPONSE;
                        avrcp_send_cmd(connection->l2cap_signaling_cid, connection);
                        return;
                    }
                }
            }
            return;
        default:
            return;
    }
}

static void avrcp_controller_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
    avrcp_connection_t * connection;

    switch (packet_type) {
        case L2CAP_DATA_PACKET:
            connection = get_avrcp_connection_for_l2cap_signaling_cid(channel, &avrcp_controller_context);
            if (!connection) break;
            avrcp_handle_l2cap_data_packet_for_signaling_connection(connection, packet, size);
            break;
        case HCI_EVENT_PACKET:
            switch (hci_event_packet_get_type(packet)){
                case L2CAP_EVENT_CAN_SEND_NOW:
                    connection = get_avrcp_connection_for_l2cap_signaling_cid(channel, &avrcp_controller_context);
                    if (!connection) break;
                    avrcp_controller_handle_can_send_now(connection);
                    break;
            default:
                avrcp_packet_handler(packet_type, channel, packet, size, &avrcp_controller_context);
                break;
        }
        default:
            break;
    }
}

void avrcp_controller_init(void){
    avrcp_controller_context.role = AVRCP_CONTROLLER;
    avrcp_controller_context.connections = NULL;
    avrcp_controller_context.packet_handler = avrcp_controller_packet_handler;
    l2cap_register_service(&avrcp_controller_packet_handler, BLUETOOTH_PROTOCOL_AVCTP, 0xffff, LEVEL_0);
}

void avrcp_controller_register_packet_handler(btstack_packet_handler_t callback){
    if (callback == NULL){
        log_error("avrcp_register_packet_handler called with NULL callback");
        return;
    }
    avrcp_controller_context.avrcp_callback = callback;
}

uint8_t avrcp_controller_connect(bd_addr_t bd_addr, uint16_t * avrcp_cid){
    return avrcp_connect(bd_addr, &avrcp_controller_context, avrcp_cid);
}

uint8_t avrcp_controller_unit_info(uint16_t avrcp_cid){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_unit_info: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    connection->state = AVCTP_W2_SEND_COMMAND;

    connection->transaction_label++;
    connection->command_opcode = AVRCP_CMD_OPCODE_UNIT_INFO;
    connection->command_type = AVRCP_CTYPE_STATUS;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_UNIT; //vendor unique
    connection->subunit_id =   AVRCP_SUBUNIT_ID_IGNORE;
    memset(connection->cmd_operands, 0xFF, connection->cmd_operands_length);
    connection->cmd_operands_length = 5;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

static uint8_t avrcp_controller_get_capabilities(uint16_t avrcp_cid, uint8_t capability_id){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_capabilities: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    connection->state = AVCTP_W2_SEND_COMMAND;

    connection->transaction_label++;
    connection->command_opcode = AVRCP_CMD_OPCODE_VENDOR_DEPENDENT;
    connection->command_type = AVRCP_CTYPE_STATUS;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_PANEL;
    connection->subunit_id = AVRCP_SUBUNIT_ID;
    big_endian_store_24(connection->cmd_operands, 0, BT_SIG_COMPANY_ID);
    connection->cmd_operands[3] = AVRCP_PDU_ID_GET_CAPABILITIES; // PDU ID
    connection->cmd_operands[4] = 0;
    big_endian_store_16(connection->cmd_operands, 5, 1); // parameter length
    connection->cmd_operands[7] = capability_id;                  // capability ID
    connection->cmd_operands_length = 8;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

uint8_t avrcp_controller_get_supported_company_ids(uint16_t avrcp_cid){
    return avrcp_controller_get_capabilities(avrcp_cid, AVRCP_CAPABILITY_ID_COMPANY);
}

uint8_t avrcp_controller_get_supported_events(uint16_t avrcp_cid){
    return avrcp_controller_get_capabilities(avrcp_cid, AVRCP_CAPABILITY_ID_EVENT);
}


uint8_t avrcp_controller_play(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_PLAY, 0);
}

uint8_t avrcp_controller_stop(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_STOP, 0);
}

uint8_t avrcp_controller_pause(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_PAUSE, 0);
}

uint8_t avrcp_controller_forward(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_FORWARD, 0);
}

uint8_t avrcp_controller_backward(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_BACKWARD, 0);
}

uint8_t avrcp_controller_start_rewind(uint16_t avrcp_cid){
    return request_continuous_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_REWIND, 0);
}

uint8_t avrcp_controller_volume_up(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_VOLUME_UP, 0);
}

uint8_t avrcp_controller_volume_down(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_VOLUME_DOWN, 0);
}

uint8_t avrcp_controller_mute(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_MUTE, 0);
}

uint8_t avrcp_controller_skip(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_SKIP, 0);
}

uint8_t avrcp_controller_stop_rewind(uint16_t avrcp_cid){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_stop_rewind: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_W4_STOP) return ERROR_CODE_COMMAND_DISALLOWED;
    return request_pass_through_release_control_cmd(connection);
}

uint8_t avrcp_controller_start_fast_forward(uint16_t avrcp_cid){
    return request_continuous_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_FAST_FORWARD, 0);
}

uint8_t avrcp_controller_fast_forward(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_FAST_FORWARD, 0);
}

uint8_t avrcp_controller_rewind(uint16_t avrcp_cid){
    return request_single_pass_through_press_control_cmd(avrcp_cid, AVRCP_OPERATION_ID_REWIND, 0);
}


uint8_t avrcp_controller_stop_fast_forward(uint16_t avrcp_cid){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_stop_fast_forward: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_W4_STOP) return ERROR_CODE_COMMAND_DISALLOWED;
    return request_pass_through_release_control_cmd(connection);
}

uint8_t avrcp_controller_get_play_status(uint16_t avrcp_cid){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_play_status: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    connection->state = AVCTP_W2_SEND_COMMAND;
    connection->transaction_label++;
    connection->command_opcode = AVRCP_CMD_OPCODE_VENDOR_DEPENDENT;
    connection->command_type = AVRCP_CTYPE_STATUS;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_PANEL;
    connection->subunit_id = AVRCP_SUBUNIT_ID;
    big_endian_store_24(connection->cmd_operands, 0, BT_SIG_COMPANY_ID);
    connection->cmd_operands[3] = AVRCP_PDU_ID_GET_PLAY_STATUS;
    connection->cmd_operands[4] = 0;                     // reserved(upper 6) | packet_type -> 0
    big_endian_store_16(connection->cmd_operands, 5, 0); // parameter length
    connection->cmd_operands_length = 7;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

uint8_t avrcp_controller_enable_notification(uint16_t avrcp_cid, avrcp_notification_event_id_t event_id){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_play_status: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    avrcp_register_notification(connection, event_id);
    return ERROR_CODE_SUCCESS;
}

uint8_t avrcp_controller_disable_notification(uint16_t avrcp_cid, avrcp_notification_event_id_t event_id){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_play_status: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    connection->notifications_to_deregister |= (1 << event_id);
    return ERROR_CODE_SUCCESS;
}

uint8_t avrcp_controller_get_now_playing_info(uint16_t avrcp_cid){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_capabilities: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    connection->state = AVCTP_W2_SEND_COMMAND;

    connection->transaction_label++;
    connection->command_opcode = AVRCP_CMD_OPCODE_VENDOR_DEPENDENT;
    connection->command_type = AVRCP_CTYPE_STATUS;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_PANEL;
    connection->subunit_id = AVRCP_SUBUNIT_ID;
    int pos = 0;
    big_endian_store_24(connection->cmd_operands, pos, BT_SIG_COMPANY_ID);
    pos += 3;
    connection->cmd_operands[pos++] = AVRCP_PDU_ID_GET_ELEMENT_ATTRIBUTES; // PDU ID
    connection->cmd_operands[pos++] = 0;

    // Parameter Length
    big_endian_store_16(connection->cmd_operands, pos, 9);
    pos += 2;

    // write 8 bytes value
    memset(connection->cmd_operands + pos, 0, 8); // identifier: PLAYING
    pos += 8;

    connection->cmd_operands[pos++] = 0; // attribute count, if 0 get all attributes
    // every attribute is 4 bytes long

    connection->cmd_operands_length = pos;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

uint8_t avrcp_controller_set_absolute_volume(uint16_t avrcp_cid, uint8_t volume){
     avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_capabilities: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    connection->state = AVCTP_W2_SEND_COMMAND;

    connection->transaction_label++;
    connection->command_opcode = AVRCP_CMD_OPCODE_VENDOR_DEPENDENT;
    connection->command_type = AVRCP_CTYPE_CONTROL;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_PANEL;
    connection->subunit_id = AVRCP_SUBUNIT_ID;
    int pos = 0;
    big_endian_store_24(connection->cmd_operands, pos, BT_SIG_COMPANY_ID);
    pos += 3;
    connection->cmd_operands[pos++] = AVRCP_PDU_ID_SET_ABSOLUTE_VOLUME; // PDU ID
    connection->cmd_operands[pos++] = 0;

    // Parameter Length
    big_endian_store_16(connection->cmd_operands, pos, 1);
    pos += 2;
    connection->cmd_operands[pos++] = volume;

    connection->cmd_operands_length = pos;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

uint8_t avrcp_controller_query_shuffle_and_repeat_modes(uint16_t avrcp_cid){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_capabilities: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    connection->state = AVCTP_W2_SEND_COMMAND;

    connection->transaction_label++;
    connection->command_opcode = AVRCP_CMD_OPCODE_VENDOR_DEPENDENT;
    connection->command_type = AVRCP_CTYPE_STATUS;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_PANEL;
    connection->subunit_id = AVRCP_SUBUNIT_ID;
    big_endian_store_24(connection->cmd_operands, 0, BT_SIG_COMPANY_ID);
    connection->cmd_operands[3] = AVRCP_PDU_ID_GetCurrentPlayerApplicationSettingValue; // PDU ID
    connection->cmd_operands[4] = 0;
    big_endian_store_16(connection->cmd_operands, 5, 5); // parameter length
    connection->cmd_operands[7] = 4;                     // NumPlayerApplicationSettingAttributeID
    // PlayerApplicationSettingAttributeID1 AVRCP Spec, Appendix F, 133
    connection->cmd_operands[8]  = 0x01;    // equalizer  (1-OFF, 2-ON)
    connection->cmd_operands[9]  = 0x02;    // repeat     (1-off, 2-single track, 3-all tracks, 4-group repeat)
    connection->cmd_operands[10] = 0x03;    // shuffle    (1-off, 2-all tracks, 3-group shuffle)
    connection->cmd_operands[11] = 0x04;    // scan       (1-off, 2-all tracks, 3-group scan)
    connection->cmd_operands_length = 12;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

static uint8_t avrcp_controller_set_current_player_application_setting_value(uint16_t avrcp_cid, uint8_t attr_id, uint8_t attr_value){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_capabilities: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    connection->state = AVCTP_W2_SEND_COMMAND;

    connection->transaction_label++;
    connection->command_opcode = AVRCP_CMD_OPCODE_VENDOR_DEPENDENT;
    connection->command_type = AVRCP_CTYPE_CONTROL;
    connection->subunit_type = AVRCP_SUBUNIT_TYPE_PANEL;
    connection->subunit_id = AVRCP_SUBUNIT_ID;
    int pos = 0;
    big_endian_store_24(connection->cmd_operands, pos, BT_SIG_COMPANY_ID);
    pos += 3;
    connection->cmd_operands[pos++] = AVRCP_PDU_ID_SetPlayerApplicationSettingValue; // PDU ID
    connection->cmd_operands[pos++] = 0;
    // Parameter Length
    big_endian_store_16(connection->cmd_operands, pos, 3);
    pos += 2;
    connection->cmd_operands[pos++] = 2;
    connection->cmd_operands_length = pos;
    connection->cmd_operands[pos++]  = attr_id;
    connection->cmd_operands[pos++]  = attr_value;
    connection->cmd_operands_length = pos;
    avrcp_request_can_send_now(connection, connection->l2cap_signaling_cid);
    return ERROR_CODE_SUCCESS;
}

uint8_t avrcp_controller_set_shuffle_mode(uint16_t avrcp_cid, avrcp_shuffle_mode_t mode){
    if (mode < AVRCP_SHUFFLE_MODE_OFF || mode > AVRCP_SHUFFLE_MODE_GROUP) return ERROR_CODE_UNSUPPORTED_FEATURE_OR_PARAMETER_VALUE;
    return avrcp_controller_set_current_player_application_setting_value(avrcp_cid, 0x03, mode);
}

uint8_t avrcp_controller_set_repeat_mode(uint16_t avrcp_cid, avrcp_repeat_mode_t mode){
    if (mode < AVRCP_REPEAT_MODE_OFF || mode > AVRCP_REPEAT_MODE_GROUP) return ERROR_CODE_UNSUPPORTED_FEATURE_OR_PARAMETER_VALUE;
    return avrcp_controller_set_current_player_application_setting_value(avrcp_cid, 0x02, mode);
}

uint8_t avrcp_controller_disconnect(uint16_t avrcp_cid){
    avrcp_connection_t * connection = get_avrcp_connection_for_avrcp_cid(avrcp_cid, &avrcp_controller_context);
    if (!connection){
        log_error("avrcp_get_capabilities: could not find a connection.");
        return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
    }
    if (connection->state != AVCTP_CONNECTION_OPENED) return ERROR_CODE_COMMAND_DISALLOWED;
    l2cap_disconnect(connection->l2cap_signaling_cid, 0);
    return ERROR_CODE_SUCCESS;
}