Muitas pessoas são movidas por desafios, e eu não sou diferente. Desde que eu recebi o meu primeiro ESP32 da SparkFun, fiquei interessado mais na questão de ter um Bluetooth junto com o WiFi do que qualquer outro atributo do ESP32.

E ai vieram as primeiras decepções, que muitos usuários do ESP32 já estavam enfrentando. Além da falta de documentação em relação ao uso do Bluetooth, algumas pessoas estavam relatando que a Espressif ainda não tinha terminado toda a implementação da pilha, parei de me interessar em fazer funcionar.

Eis que surge uma oportunidade de usar o Bluetooth no ESP32. Fiz a devida atualização da plataforma ESP-IDF, que já tratamos aqui anteriormente e comecei a ler novamente a documentação.

Descobri que ainda estavam faltando alguns detalhes e que não seria tarefa trivial utilizar, mesmo que alguns testes dos exemplos prontos funcionavam com BLE, mas não com Bluetooth Classic. Não poderia utilizar a pilha da Espressif.

Na minha busca em alternativas, me deparei com a BTstack da BlueKitchen, que é uma pilha de Bluetooth que suporta SPP (Serial Port Profile) e tem suporte para o ESP32.

Instalando a BTstack

Para instalar a BTstack, devemos antes instalar o ESP-IDF, que pode ser feito por este link.

Feita a instalação do ESP-IDF, devemos fazer o clone do repositorio na mesma pasta em que está a pasta esp-idf, no meu caso a pasta /home/pedro/esp.

No terminal:

$ git clone https://github.com/bluekitchen/btstack.git

Vá para a pasta btstack/port/esp32/.

$ cd btstack/port/esp32/

Execute o comando:

./integrate_btstack.py

Neste ponto, a BTstack deverá aparecer dentro da pasta components do ESP-IDF

../esp/esp-idf/components/btstack/

Neste diretório temos os exemplos para fazer diversos testes, mas vamos focar no Bluetooth Classic com SPP, muito utilizado em projetos maker.

O exemplo “spp_counter”, será o nosso exemplo base, e com algumas alterações podemos realizar os mais diversos tipos de integração.

Código fonte de teste

/*
 * 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 
 * contact@bluekitchen-gmbh.com
 *
 */

#define __BTSTACK_FILE__ "spp_counter.c"

// *****************************************************************************
/* EXAMPLE_START(spp_counter): SPP Server - Heartbeat Counter over RFCOMM
 *
 * @text The Serial port profile (SPP) is widely used as it provides a serial
 * port over Bluetooth. The SPP counter example demonstrates how to setup an SPP
 * service, and provide a periodic timer over RFCOMM.   
 */
// *****************************************************************************

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

#define RFCOMM_SERVER_CHANNEL 1
#define HEARTBEAT_PERIOD_MS 1000

static char lineBuffer[30];

static void packet_handler (uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size);

static uint16_t rfcomm_channel_id;
static uint8_t  spp_service_buffer[150];
static btstack_packet_callback_registration_t hci_event_callback_registration;


/* @section SPP Service Setup 
 *s
 * @text To provide an SPP service, the L2CAP, RFCOMM, and SDP protocol layers 
 * are required. After setting up an RFCOMM service with channel nubmer
 * RFCOMM_SERVER_CHANNEL, an SDP record is created and registered with the SDP server.
 * Example code for SPP service setup is
 * provided in Listing SPPSetup. The SDP record created by function
 * spp_create_sdp_record consists of a basic SPP definition that uses the provided
 * RFCOMM channel ID and service name. For more details, please have a look at it
 * in \path{src/sdp_util.c}. 
 * The SDP record is created on the fly in RAM and is deterministic.
 * To preserve valuable RAM, the result could be stored as constant data inside the ROM.   
 */

/* LISTING_START(SPPSetup): SPP service setup */ 
static void spp_service_setup(void){

    // register for HCI events
    hci_event_callback_registration.callback = &packet_handler;
    hci_add_event_handler(&hci_event_callback_registration);

    l2cap_init();

    rfcomm_init();
    rfcomm_register_service(packet_handler, RFCOMM_SERVER_CHANNEL, 0xffff);  // reserved channel, mtu limited by l2cap

    // init SDP, create record for SPP and register with SDP
    sdp_init();
    memset(spp_service_buffer, 0, sizeof(spp_service_buffer));
    spp_create_sdp_record(spp_service_buffer, 0x10001, RFCOMM_SERVER_CHANNEL, "SPP Counter");
    sdp_register_service(spp_service_buffer);
    printf("SDP service record size: %u\n", de_get_len(spp_service_buffer));
}
/* LISTING_END */

/* @section Bluetooth Logic 
 * @text The Bluetooth logic is implemented within the 
 * packet handler, see Listing SppServerPacketHandler. In this example, 
 * the following events are passed sequentially: 
 * - BTSTACK_EVENT_STATE,
 * - HCI_EVENT_PIN_CODE_REQUEST (Standard pairing) or 
 * - HCI_EVENT_USER_CONFIRMATION_REQUEST (Secure Simple Pairing),
 * - RFCOMM_EVENT_INCOMING_CONNECTION,
 * - RFCOMM_EVENT_CHANNEL_OPENED, 
* - RFCOMM_EVETN_CAN_SEND_NOW, and
 * - RFCOMM_EVENT_CHANNEL_CLOSED
 */

/* @text Upon receiving HCI_EVENT_PIN_CODE_REQUEST event, we need to handle
 * authentication. Here, we use a fixed PIN code "0000".
 *
 * When HCI_EVENT_USER_CONFIRMATION_REQUEST is received, the user will be 
 * asked to accept the pairing request. If the IO capability is set to 
 * SSP_IO_CAPABILITY_DISPLAY_YES_NO, the request will be automatically accepted.
 *
 * The RFCOMM_EVENT_INCOMING_CONNECTION event indicates an incoming connection.
 * Here, the connection is accepted. More logic is need, if you want to handle connections
 * from multiple clients. The incoming RFCOMM connection event contains the RFCOMM
 * channel number used during the SPP setup phase and the newly assigned RFCOMM
 * channel ID that is used by all BTstack commands and events.
 *
 * If RFCOMM_EVENT_CHANNEL_OPENED event returns status greater then 0,
 * then the channel establishment has failed (rare case, e.g., client crashes).
 * On successful connection, the RFCOMM channel ID and MTU for this
 * channel are made available to the heartbeat counter. After opening the RFCOMM channel, 
 * the communication between client and the application
 * takes place. In this example, the timer handler increases the real counter every
 * second. 
 *
 * RFCOMM_EVENT_CAN_SEND_NOW indicates that it's possible to send an RFCOMM packet
 * on the rfcomm_cid that is include

 */ 

/* LISTING_START(SppServerPacketHandler): SPP Server - Heartbeat Counter over RFCOMM */
static void packet_handler (uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
    UNUSED(channel);

/* LISTING_PAUSE */ 
    bd_addr_t event_addr;
    uint8_t   rfcomm_channel_nr;
    uint16_t  mtu;
    int i;

    switch (packet_type) {
        case HCI_EVENT_PACKET:
            switch (hci_event_packet_get_type(packet)) {
/* LISTING_RESUME */ 
                case HCI_EVENT_PIN_CODE_REQUEST:
                    // inform about pin code request
                    printf("Pin code request - using '0000'\n");
                    hci_event_pin_code_request_get_bd_addr(packet, event_addr);
                    gap_pin_code_response(event_addr, "0000");
                    break;

                case HCI_EVENT_USER_CONFIRMATION_REQUEST:
                    // ssp: inform about user confirmation request
                    printf("SSP User Confirmation Request with numeric value '%06"PRIu32"'\n", little_endian_read_32(packet, 8));
                    printf("SSP User Confirmation Auto accept\n");
                    break;

                case RFCOMM_EVENT_INCOMING_CONNECTION:
                    // data: event (8), len(8), address(48), channel (8), rfcomm_cid (16)
                    rfcomm_event_incoming_connection_get_bd_addr(packet, event_addr); 
                    rfcomm_channel_nr = rfcomm_event_incoming_connection_get_server_channel(packet);
                    rfcomm_channel_id = rfcomm_event_incoming_connection_get_rfcomm_cid(packet);
                    printf("RFCOMM channel %u requested for %s\n", rfcomm_channel_nr, bd_addr_to_str(event_addr));
                    rfcomm_accept_connection(rfcomm_channel_id);
                    break;
               
                case RFCOMM_EVENT_CHANNEL_OPENED:
                    // data: event(8), len(8), status (8), address (48), server channel(8), rfcomm_cid(16), max frame size(16)
                    if (rfcomm_event_channel_opened_get_status(packet)) {
                        printf("RFCOMM channel open failed, status %u\n", rfcomm_event_channel_opened_get_status(packet));
                    } else {
                        rfcomm_channel_id = rfcomm_event_channel_opened_get_rfcomm_cid(packet);
                        mtu = rfcomm_event_channel_opened_get_max_frame_size(packet);
                        printf("RFCOMM channel open succeeded. New RFCOMM Channel ID %u, max frame size %u\n", rfcomm_channel_id, mtu);
                    }
                    break;
                case RFCOMM_EVENT_CAN_SEND_NOW:
                    rfcomm_send(rfcomm_channel_id, (uint8_t*) lineBuffer, strlen(lineBuffer));  
                    break;

/* LISTING_PAUSE */                 
                case RFCOMM_EVENT_CHANNEL_CLOSED:
                    printf("RFCOMM channel closed\n");
                    rfcomm_channel_id = 0;
                    break;
                
                default:
                    break;
            }
            break;

        case RFCOMM_DATA_PACKET:
            printf("Recebido: ");

            for (i=0;i<size;i++){
                putchar(packet[i]);
            }

	    if (rfcomm_channel_id){
                sprintf(lineBuffer, "Loopback %s\n", packet);
                rfcomm_request_can_send_now_event(rfcomm_channel_id);
            }

            break;

        default:
            break;
    }
/* LISTING_RESUME */ 
}
/* LISTING_END */

int btstack_main(int argc, const char * argv[]);

int btstack_main(int argc, const char * argv[]){
    (void)argc;
    (void)argv;

    spp_service_setup();

    gap_discoverable_control(1);
    gap_ssp_set_io_capability(SSP_IO_CAPABILITY_DISPLAY_YES_NO);
    gap_set_local_name("ESP32-Serial");

    // turn on!
    hci_power_control(HCI_POWER_ON);
    
    return 0;
}

Para testar o funcionamento, utilizei o programa para Android “Bluetooth Terminal HC-05”.

Conclusão

Pelos teste que fiz, pude notar que a BTstack foi a melhor opção para SPP em modo Bluetooth Classic. Não posso dizer em relação aos outros exemplos, pois não utilizei a ponto de tirar alguma conclusão.

O que posso dizer é que eu fiquei muito satisfeito com a documentação e com os exemplos prontos que a Bluekitchen disponibilizou.

Happy Hacking and Happy 2018!