ExpressLRS - ELRS TX Simple Code for ESP32

ELRS_TX_SimpleCode.cpp

#include <M5Stack.h>

#define PACKED __attribute__((packed))

#define SERIAL_BAUDRATE 420000  // ELRS モジュールの通信速度

#define GPIO_PIN_RCSIGNAL_TX 21 // ELRS TX モジュールとの接続ピン（半二重）
#define GPIO_PIN_RCSIGNAL_RX 21 // ELRS TX モジュールとの接続ピン（半二重）


// CRC8 計算
#define CRSF_CRC_POLY 0xd5

static byte getCRC8(byte *buf, size_t size)
{
  byte crc8 = 0x00;

  for (int i = 0; i < size; i++)
  {
    crc8 ^= buf[i];

    for (int j = 0; j < 8; j++)
    {
      if (crc8 & 0x80)
      {
        crc8 <<= 1;
        crc8 ^= CRSF_CRC_POLY;
      }
      else
      {
        crc8 <<= 1;
      }
    }
  }
  return crc8;
}

void ICACHE_RAM_ATTR duplex_set_TX()
{
  portDISABLE_INTERRUPTS();

  gpio_set_pull_mode((gpio_num_t)GPIO_PIN_RCSIGNAL_TX, GPIO_FLOATING);
  gpio_set_pull_mode((gpio_num_t)GPIO_PIN_RCSIGNAL_RX, GPIO_FLOATING);
  gpio_set_level((gpio_num_t)GPIO_PIN_RCSIGNAL_TX, 1);
  gpio_set_direction((gpio_num_t)GPIO_PIN_RCSIGNAL_TX, GPIO_MODE_OUTPUT);
  constexpr uint8_t MATRIX_DETACH_IN_HIGH = 0x38;             // routes 1 to matrix slot
  gpio_matrix_in(MATRIX_DETACH_IN_HIGH, U1RXD_IN_IDX, false); // Disconnect RX from all pads
  gpio_matrix_out((gpio_num_t)GPIO_PIN_RCSIGNAL_TX, U1TXD_OUT_IDX, false, false);

  portENABLE_INTERRUPTS();
}

/**
 * Define the shape of a standard header
 */
typedef struct crsf_header_s
{
  uint8_t device_addr; // from crsf_addr_e
  uint8_t frame_size;  // counts size after this byte, so it must be the payload size + 2 (type and crc)
  uint8_t type;        // from crsf_frame_type_e
} PACKED crsf_header_t;

/**
 * Crossfire packed channel structure, each channel is 11 bits
 */
typedef struct crsf_channels_s
{
  unsigned ch0 : 11;
  unsigned ch1 : 11;
  unsigned ch2 : 11;
  unsigned ch3 : 11;
  unsigned ch4 : 11;
  unsigned ch5 : 11;
  unsigned ch6 : 11;
  unsigned ch7 : 11;
  unsigned ch8 : 11;
  unsigned ch9 : 11;
  unsigned ch10 : 11;
  unsigned ch11 : 11;
  unsigned ch12 : 11;
  unsigned ch13 : 11;
  unsigned ch14 : 11;
  unsigned ch15 : 11;
} PACKED crsf_channels_t;
typedef struct  {
  crsf_header_t header;
  crsf_channels_t ch; // payload

  byte crc = 0xff;
} PACKED RC_CHANNEL;

#define CRSF_ADDRESS_FLIGHT_CONTROLLER    0xC8
#define CRSF_ADDRESS_CRSF_TRANSMITTER     0xEE
#define CRSF_FRAMETYPE_RC_CHANNELS_PACKED 0x16

static RC_CHANNEL rc;

void setup()
{
  M5.begin();
  Serial1.begin(SERIAL_BAUDRATE, SERIAL_8N1, -1, GPIO_PIN_RCSIGNAL_TX, false, 500);
  delay(200);
}

void loop()
{

  // CRSFパケット ヘッダ
  rc.header.device_addr = CRSF_ADDRESS_CRSF_TRANSMITTER;
  rc.header.frame_size = sizeof(RC_CHANNEL)-2;
  rc.header.type = CRSF_FRAMETYPE_RC_CHANNELS_PACKED;

  // プロポのチャンネル情報を書き換える
  rc.ch.ch0 += 1;
  rc.ch.ch1 += 2;
  rc.ch.ch2 += 3;
  rc.ch.ch3 += 4;

  // CRC計算
  rc.crc = getCRC8(&rc.header.type, rc.header.frame_size-1);

  // 半二重 送信モードへ
  duplex_set_TX();

  // 送信
  Serial1.write((byte *)&rc, sizeof(RC_CHANNEL));

  delay(1);
}

受信の最小限のコードはこちら。

https://gist.github.com/GOROman/e194f501fbbfce589767966ce4241c6d

https://github.com/ExpressLRS/ExpressLRS/wiki/CRSF-Protocol

PING Packet
byte ping[] = {0xEE, 0x04, 0x28, 0x00, 0xEA, 0x54};