/** * @file DShotRMT.cpp * @brief DShot signal generation using ESP32 RMT with continuous repeat and pause between frames, including BiDirectional support * @author Wastl Kraus * @date 2025-06-11 * @license MIT */ #include // --- DShotRMT Class --- // This class provides an abstraction for sending and optionally receiving DShot frames. // It uses ESP32's RMT peripheral for precise timing control, including BiDirectional RX. DShotRMT::DShotRMT(gpio_num_t gpio, dshot_mode_t mode, bool isBidirectional) : _gpio(gpio), _mode(mode), _isBidirectional(isBidirectional) {} // Sets up RMT TX and RX channels as well as encoder configuration void DShotRMT::begin() { // TX RMT Channel Configuration _rmt_tx_channel_config = { .gpio_num = _gpio, .clk_src = DSHOT_CLOCK_SRC_DEFAULT, .resolution_hz = DSHOT_RMT_RESOLUTION, .mem_block_symbols = 64, .trans_queue_depth = 2, // .flags = { // invert Signal if BiDirectional DShot Mode // .invert_out = _isBidirectional, // .with_dma = false} }; rmt_new_tx_channel(&_rmt_tx_channel_config, &_rmt_tx_channel); rmt_enable(_rmt_tx_channel); // RX RMT Channel Configuration (for BiDirectional DShot) if (_isBidirectional) { _rmt_rx_channel_config = { .gpio_num = _gpio, .clk_src = DSHOT_CLOCK_SRC_DEFAULT, .resolution_hz = DSHOT_RMT_RESOLUTION, .mem_block_symbols = 64, // .flags = { // .invert_in = false, // .with_dma = false} }; rmt_new_rx_channel(&_rmt_rx_channel_config, &_rmt_rx_channel); rmt_enable(_rmt_rx_channel); _receive_config.signal_range_min_ns = 300; _receive_config.signal_range_max_ns = 5000; } // Use a copy encoder to send raw symbols if (!_dshot_encoder) { rmt_copy_encoder_config_t enc_cfg = {}; rmt_new_copy_encoder(&enc_cfg, &_dshot_encoder); } // Configure transmission looping _transmit_config.loop_count = 0; _transmit_config.flags.eot_level = _isBidirectional; } // Encodes and transmits a valid DShot Throttle value (48 - 2047) void DShotRMT::setThrottle(uint16_t throttle) { // Safety first - double check input range and 11 bit "translation" throttle = constrain(throttle, DSHOT_THROTTLE_MIN, DSHOT_THROTTLE_MAX) & 0b0000011111111111; _lastThrottle = throttle; // Convert throttle value to DShot Paket Format _tx_packet = assambleDShotPaket(_lastThrottle); // Encode RMT symbols size_t count = 0; encodeDShotTX(_tx_packet, _tx_symbols, count); // Send the packet rmt_transmit(_rmt_tx_channel, _dshot_encoder, _tx_symbols, count * sizeof(rmt_symbol_word_t), &_transmit_config); // Take a break esp_rom_delay_us(120); } // --- Get eRPM from ESC --- // Receives and decodes a response frame from ESC containing eRPM info uint32_t DShotRMT::getERPM() { if (_isBidirectional) { if (_rmt_rx_channel == nullptr) return _last_erpm; // Attempt to receive a new frame if (!rmt_receive(_rmt_rx_channel, _rx_symbols, sizeof(_rx_symbols), &_receive_config)) return _last_erpm; // _last_erpm = decodeDShotRX(_rx_symbols, DSHOT_BITS_PER_FRAME); return _last_erpm; } // Nothing to do here return _last_erpm; } // Translate eRPM value to RPM taking magnet count as parameter uint32_t DShotRMT::getMotorRPM(uint8_t magnet_count) { uint8_t pole_count = magnet_count / 2; if (pole_count == 0) pole_count = 1; uint32_t rpm = getERPM() / pole_count; return rpm; } // Calculate CRC for DShot Paket uint16_t DShotRMT::calculateCRC(uint16_t dshot_packet) { uint16_t _packet = (dshot_packet << 1) | (_isBidirectional ? 1 : 0); // Clear container before new calculation _packet_crc = DSHOT_NULL_PACKET; // CRC calculation for DShot (4 bits) _packet_crc = ((_packet ^ (_packet >> 4) ^ (_packet >> 8)) & 0b0000000000001111); // CRC is inverted for biDirectional DShot if (_isBidirectional) _packet_crc = (~_packet_crc) & 0b0000000000001111; return _packet_crc; } // Assamble DShot Paket (11 bit throttle + 1 bit telemetry request + 4 bit crc) uint16_t DShotRMT::assambleDShotPaket(uint16_t value) { // Dummy conversion to 11 bits uint16_t _value = value & 0b0000011111111111; // Clear container _tx_packet = DSHOT_NULL_PACKET; // Assemble raw DShot packet and add checksum _packet_crc = calculateCRC(_value); _tx_packet = (_value << 1) | (_isBidirectional ? 1 : 0); _tx_packet = (_tx_packet << 4) | _packet_crc; return _tx_packet; } // --- Encode DShot TX Frame --- // Converts a 16-bit packet into a valid DShot Frame for RMT void DShotRMT::encodeDShotTX(uint16_t dshot_packet, rmt_symbol_word_t *symbols, size_t &count) { // Always start encoding from the top count = 0; uint32_t ticks_per_bit = 0; uint32_t ticks_zero_high = 0; uint32_t ticks_one_high = 0; switch (_mode) { case DSHOT150: ticks_per_bit = 64; ticks_zero_high = 24; ticks_one_high = 48; break; case DSHOT300: ticks_per_bit = 32; ticks_zero_high = 12; ticks_one_high = 24; break; case DSHOT600: ticks_per_bit = 16; ticks_zero_high = 6; ticks_one_high = 12; break; case DSHOT1200: ticks_per_bit = 8; ticks_zero_high = 3; ticks_one_high = 6; break; case DSHOT_OFF: default: ticks_per_bit = 0; ticks_zero_high = 0; ticks_one_high = 0; break; } uint32_t ticks_zero_low = ticks_per_bit - ticks_zero_high; uint32_t ticks_one_low = ticks_per_bit - ticks_one_high; // Fill the 16 DShot-Bits Array with selected timings for (int i = 15; i >= 0; i--) { bool bit = (dshot_packet >> i) & 0x01; if (_isBidirectional) { symbols[count].level0 = 0; symbols[count].duration0 = bit ? ticks_one_high : ticks_zero_high; symbols[count].level1 = 1; symbols[count].duration1 = bit ? ticks_one_low : ticks_zero_low; } else { symbols[count].level0 = 1; symbols[count].duration0 = bit ? ticks_one_high : ticks_zero_high; symbols[count].level1 = 0; symbols[count].duration1 = bit ? ticks_one_low : ticks_zero_low; } count++; } } // Decodes a response frame from ESC containing eRPM info uint16_t DShotRMT::decodeDShotRX(const rmt_symbol_word_t *symbols, uint32_t count) { // Container for received frame uint16_t _rec_frame = DSHOT_NULL_PACKET; // Fill the Frame bit by bit for (size_t i = 0; i < DSHOT_BITS_PER_FRAME && i < count; ++i) { bool bit = (symbols[i].duration0 < symbols[i].duration1); _rec_frame = (_rec_frame << 1) | bit; } // Store the received CRC for checking uint16_t _temp = _rec_frame >> 4; // Masking the received CRC uint8_t crc_recv = _rec_frame & 0x0F; // Calculate CRC for received frame again uint8_t crc_calc = (_temp ^ (_temp >> 4) ^ (_temp >> 8)) & 0b0000000000001111; if (_isBidirectional) crc_calc = (~crc_calc) & 0x0F; // Checking CRC if (crc_recv != crc_calc) return _last_erpm; // Cut "telemetric" bit leaving "raw" value uint16_t raw = _temp >> 1; return _last_erpm = raw; }