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DShotRMT
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...update CRC calculation 

...simplified CRC calculation
This commit is contained in:
Wastl Kraus 2025-09-01 16:31:50 +02:00
parent e016bb3985
commit 759b7ef63c
2 changed files with 24 additions and 34 deletions
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50
DShotRMT.cpp
View File

@ -278,13 +278,17 @@ uint32_t DShotRMT::getMotorRPM(uint8_t magnet_count)
// Build a complete DShot packet
dshot_packet_t DShotRMT::_buildDShotPacket(const uint16_t value)
{
// Initialize packet structure
// Init packet structure
dshot_packet_t packet = {};
// Build packet
packet.throttle_value = value;
packet.telemetric_request = _is_bidirectional ? 1 : 0;
packet.checksum = _calculateCRC(packet);
// CRC is calculated over 11bit
uint16_t data = (packet.throttle_value << 1) | packet.telemetric_request;
packet.checksum = _calculateCRC(data);
return packet;
}
@ -292,18 +296,17 @@ dshot_packet_t DShotRMT::_buildDShotPacket(const uint16_t value)
// Parse DShot packet into 16-bit format
uint16_t DShotRMT::_parseDShotPacket(const dshot_packet_t &packet)
{
uint16_t data = (packet.throttle_value << 1) | packet.telemetric_request;
// Parse DShot frame into "raw" 16 bit value
uint16_t data_and_telemetry = (packet.throttle_value << 1) | packet.telemetric_request;
uint16_t parsed_packet = (data_and_telemetry << 4) | packet.checksum;
// Add CRC checksum
return (data << 4) | _calculateCRC(packet);
return parsed_packet;
}
// Calculate CRC checksum
uint16_t DShotRMT::_calculateCRC(const dshot_packet_t &packet)
// Calculate CRC
uint16_t DShotRMT::_calculateCRC(const uint16_t data)
{
uint16_t data = (packet.throttle_value << 1) | packet.telemetric_request;
// DShot CRC calculation
// DShot CRC
uint16_t crc = (data ^ (data >> 4) ^ (data >> 8)) & 0b0000000000001111;
// Invert CRC for bidirectional DShot mode
@ -421,32 +424,19 @@ uint16_t DShotRMT::_decodeDShotFrame(const rmt_symbol_word_t *symbols)
// Extract CRC from gcr answer
uint16_t received_crc = raw_gcr_data & 0b0000000000001111;
// Decode GCR-encoded 10-bit value to get the original 10-bit value and check CRC
uint16_t received_data = 0;
// GCR first bit is XORed with 1
uint16_t last_bit = 1;
for (int i = 0; i < 10; ++i)
{
bool current_bit = (raw_gcr_data >> (15 - i)) & 1;
bool decoded_bit = current_bit ^ last_bit;
received_data |= (decoded_bit << (9 - i));
last_bit = current_bit;
}
// Calculate CRC from the received and decoded data
uint16_t calculated_crc = (received_data ^ (received_data >> 4) ^ (received_data >> 8)) & 0b0000000000001111;
// Validate CRC (inverted for bidirectional DShot)
if (received_crc != ((~calculated_crc) & 0b0000000000001111))
// Calculate expected CRC using the new, centralized function
uint16_t data_for_crc = (decoded_value << 1) | 1; // Telemetry request bit is always 1 for bidirectional
uint16_t calculated_crc = _calculateCRC(data_for_crc);
// Validate CRC
if (received_crc != calculated_crc)
{
_dshot_log(CRC_CHECK_FAILED);
return DSHOT_NULL_PACKET;
}
// The data is eRPM * 100
return received_data;
return decoded_value;
}
// Check if enough time has passed for next transmission

8
DShotRMT.h
View File

@ -38,7 +38,7 @@ constexpr uint32_t DSHOT_PULSE_MIN = 3000;
constexpr uint32_t DSHOT_PULSE_MAX = 60000;
// DShot Mode Enumeration
typedef enum dshot_mode_e
typedef enum
{
DSHOT_OFF,
DSHOT150,
@ -48,7 +48,7 @@ typedef enum dshot_mode_e
} dshot_mode_t;
// DShot Packet Structure
typedef struct dshot_packet_s
typedef struct
{
uint16_t throttle_value : 11;
uint16_t telemetric_request : 1;
@ -56,7 +56,7 @@ typedef struct dshot_packet_s
} dshot_packet_t;
// DShot Timing Configuration Structure
typedef struct dshot_timing_s
typedef struct
{
uint32_t frame_length_us;
uint16_t ticks_per_bit;
@ -149,7 +149,7 @@ private:
// --- PACKET MANAGEMENT ---
dshot_packet_t _buildDShotPacket(const uint16_t value);
uint16_t _parseDShotPacket(const dshot_packet_t &packet);
uint16_t _calculateCRC(const dshot_packet_t &packet);
uint16_t _calculateCRC(const uint16_t data);
// --- FRAME PROCESSING ---
uint16_t _sendDShotFrame(const dshot_packet_t &packet);