/** * @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::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() { // RX RMT Channel Configuration (for BiDirectional DShot) if (_isBidirectional) { rmt_rx_channel_config_t 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 = 100; _receive_config.signal_range_max_ns = 10000; } // TX RMT Channel Configuration rmt_tx_channel_config_t 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 = 1, .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); // 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 = -1; _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 10 bit "translation" throttle = (constrain(throttle, DSHOT_THROTTLE_MIN, DSHOT_THROTTLE_MAX)) & 0b0000011111111111; // Has Throttle really changed? if (throttle == _lastThrottle) return; _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); // Restart transmission with new data rmt_disable(_rmt_tx_channel); rmt_enable(_rmt_tx_channel); rmt_transmit(_rmt_tx_channel, _dshot_encoder, _tx_symbols, count * sizeof(rmt_symbol_word_t), &_transmit_config); } // --- Get eRPM from ESC --- // Receives and decodes a response frame from ESC containing eRPM info uint32_t DShotRMT::getERPM() { if (_isBidirectional) { static size_t rx_size = sizeof(_rx_symbols); if (_rmt_rx_channel == nullptr) return _last_erpm; // Attempt to receive a new frame if (!rmt_receive(_rmt_rx_channel, _rx_symbols, rx_size, &_receive_config)) return _last_erpm; uint16_t received_bits = 0; _received_packet = 0; // Decode raw RMT encoded bits for (int i = 0; i < DSHOT_BITS_PER_FRAME; ++i) { rmt_symbol_word_t symbols = _rx_symbols[i]; // Validate signal polarity if (symbols.level0 != 1 || symbols.level1 != 0) break; uint32_t total_ticks = symbols.duration0 + symbols.duration1; bool bit = (symbols.duration0 > (total_ticks / 2)); _received_packet <<= 1; _received_packet |= bit ? 1 : 0; received_bits++; } if (received_bits < 16) return _last_erpm; // Extract data & checksum from packet uint16_t packet_data = _received_packet >> 4; uint8_t recalc_packet_crc = (packet_data ^ (packet_data >> 4) ^ (packet_data >> 8)) & 0x0F; uint8_t packet_crc = _received_packet & 0x0F; if (recalc_packet_crc != packet_crc) return _last_erpm; // Assume received value is DShot eRPM uint16_t throttle = packet_data >> 1; // Filter noise values if (throttle < DSHOT_THROTTLE_MIN || throttle > DSHOT_THROTTLE_MAX) return _last_erpm; // Approximate eRPM (ESC dependent, scale factor can be tuned) _last_erpm = throttle * 100; 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) { // Clear container before new calculation _packet_crc = DSHOT_NULL_PACKET; // CRC is inverted for biDirectional DSHot _packet_crc = _isBidirectional ? (~(dshot_packet ^ (dshot_packet >> 4) ^ (dshot_packet >> 8))) & 0x0F : (dshot_packet ^ (dshot_packet >> 4) ^ (dshot_packet >> 8)) & 0x0F; return _packet_crc; } // Assamble DShot Paket (10 bit throttle + 1 bit telemetry request + 4 bit crc) uint16_t DShotRMT::assambleDShotPaket(uint16_t value) { // Clear container _tx_packet = DSHOT_NULL_PACKET; // dummy 10bit convertion _tx_packet = value & 0b0000011111111111; // Assemble raw DShot packet and add checksum _tx_packet = (value << 1) | (_isBidirectional ? 1 : 0); _packet_crc = calculateCRC(_tx_packet); _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; // Safety first 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; 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++; } // Append the Pause Bits symbols[count].level0 = 0; symbols[count].duration0 = ticks_per_bit * PAUSE_BITS; symbols[count].level1 = 0; symbols[count].duration1 = 0; count++; }