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VW MQB: Refactor CRC constants
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Big switch statement in volkswagen_mqb_checksum was refactored with map of arrays.
With this approach there's no need for specifying all 16 byte values if constant is the same for all of them.
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@JaCzekanski
JaCzekanski committed Sep 11, 2024
1 parent c43cd3a commit 6a22559
Showing 1 changed file with 63 additions and 60 deletions.
123 changes: 63 additions & 60 deletions opendbc/can/common.cc
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
#include "opendbc/can/common.h"

#include <array>
#include <unordered_map>

unsigned int honda_checksum(uint32_t address, const Signal &sig, const std::vector<uint8_t> &d) {
int s = 0;
Expand Down Expand Up @@ -112,6 +113,62 @@ struct CrcInitializer {

static CrcInitializer crcInitializer;

static const std::unordered_map<uint32_t, std::array<uint8_t, 16>> crc_mqb_constants{
// LWI_01 Steering Angle
{0x86, {0x86}},

// LH_EPS_03 Electric Power Steering
{0x9F, {0xF5}},

// Getriebe_11 Automatic Gearbox
{0xAD, {0x3F, 0x69, 0x39, 0xDC, 0x94, 0xF9, 0x14, 0x64, 0xD8, 0x6A, 0x34, 0xCE, 0xA2, 0x55, 0xB5, 0x2C}},

// ESP_21 Electronic Stability Program
{0xFD, {0xB4, 0xEF, 0xF8, 0x49, 0x1E, 0xE5, 0xC2, 0xC0, 0x97, 0x19, 0x3C, 0xC9, 0xF1, 0x98, 0xD6, 0x61}},

// ESP_05 Electronic Stability Program
{0x106, {0x07}},

// ACC_10 Automatic Cruise Control
{0x117, {0x16}},

// TSK_06 Drivetrain Coordinator
{0x120, {0xC4, 0xE2, 0x4F, 0xE4, 0xF8, 0x2F, 0x56, 0x81, 0x9F, 0xE5, 0x83, 0x44, 0x05, 0x3F, 0x97, 0xDF}},

// Motor_20 Driver Throttle Inputs
{0x121, {0xE9, 0x65, 0xAE, 0x6B, 0x7B, 0x35, 0xE5, 0x5F, 0x4E, 0xC7, 0x86, 0xA2, 0xBB, 0xDD, 0xEB, 0xB4}},

// ACC_06 Automatic Cruise Control
{0x122, {0x37, 0x7D, 0xF3, 0xA9, 0x18, 0x46, 0x6D, 0x4D, 0x3D, 0x71, 0x92, 0x9C, 0xE5, 0x32, 0x10, 0xB9}},

// HCA_01 Heading Control Assist
{0x126, {0xDA}},

// GRA_ACC_01 Steering wheel controls for ACC
{0x12B, {0x6A, 0x38, 0xB4, 0x27, 0x22, 0xEF, 0xE1, 0xBB, 0xF8, 0x80, 0x84, 0x49, 0xC7, 0x9E, 0x1E, 0x2B}},

// ACC_07 Automatic Cruise Control
{0x12E, {0xF8, 0xE5, 0x97, 0xC9, 0xD6, 0x07, 0x47, 0x21, 0x66, 0xDD, 0xCF, 0x6F, 0xA1, 0x94, 0x74, 0x63}},

// EV_Gearshift "Gear" selection data for EVs with no gearbox
{0x187, {0x7F, 0xED, 0x17, 0xC2, 0x7C, 0xEB, 0x44, 0x21, 0x01, 0xFA, 0xDB, 0x15, 0x4A, 0x6B, 0x23, 0x05}},

// ACC_02 Automatic Cruise Control
{0x30C, {0x0F}},

// SWA_01 Lane Change Assist (SpurWechselAssistent)
{0x30F, {0x0C}},

// ACC_04 Automatic Cruise Control
{0x324, {0x27}},

// Klemmen_Status_01 ignition and starting status
{0x3C0, {0xC3}},

// ESP_20 Electronic Stability Program
{0x65D, {0xAC, 0xB3, 0xAB, 0xEB, 0x7A, 0xE1, 0x3B, 0xF7, 0x73, 0xBA, 0x7C, 0x9E, 0x06, 0x5F, 0x02, 0xD9}},
};

unsigned int volkswagen_mqb_checksum(uint32_t address, const Signal &sig, const std::vector<uint8_t> &d) {
// Volkswagen uses standard CRC8 8H2F/AUTOSAR, but they compute it with
// a magic variable padding byte tacked onto the end of the payload.
Expand All @@ -128,68 +185,14 @@ unsigned int volkswagen_mqb_checksum(uint32_t address, const Signal &sig, const
// Look up and apply the magic final CRC padding byte, which permutes by CAN
// address, and additionally (for SOME addresses) by the message counter.
uint8_t counter = d[1] & 0x0F;
switch (address) {
case 0x86: // LWI_01 Steering Angle
crc ^= (uint8_t[]){0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86, 0x86}[counter];
break;
case 0x9F: // LH_EPS_03 Electric Power Steering
crc ^= (uint8_t[]){0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5, 0xF5}[counter];
break;
case 0xAD: // Getriebe_11 Automatic Gearbox
crc ^= (uint8_t[]){0x3F, 0x69, 0x39, 0xDC, 0x94, 0xF9, 0x14, 0x64, 0xD8, 0x6A, 0x34, 0xCE, 0xA2, 0x55, 0xB5, 0x2C}[counter];
break;
case 0xFD: // ESP_21 Electronic Stability Program
crc ^= (uint8_t[]){0xB4, 0xEF, 0xF8, 0x49, 0x1E, 0xE5, 0xC2, 0xC0, 0x97, 0x19, 0x3C, 0xC9, 0xF1, 0x98, 0xD6, 0x61}[counter];
break;
case 0x106: // ESP_05 Electronic Stability Program
crc ^= (uint8_t[]){0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07}[counter];
break;
case 0x117: // ACC_10 Automatic Cruise Control
crc ^= (uint8_t[]){0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16, 0x16}[counter];
break;
case 0x120: // TSK_06 Drivetrain Coordinator
crc ^= (uint8_t[]){0xC4, 0xE2, 0x4F, 0xE4, 0xF8, 0x2F, 0x56, 0x81, 0x9F, 0xE5, 0x83, 0x44, 0x05, 0x3F, 0x97, 0xDF}[counter];
break;
case 0x121: // Motor_20 Driver Throttle Inputs
crc ^= (uint8_t[]){0xE9, 0x65, 0xAE, 0x6B, 0x7B, 0x35, 0xE5, 0x5F, 0x4E, 0xC7, 0x86, 0xA2, 0xBB, 0xDD, 0xEB, 0xB4}[counter];
break;
case 0x122: // ACC_06 Automatic Cruise Control
crc ^= (uint8_t[]){0x37, 0x7D, 0xF3, 0xA9, 0x18, 0x46, 0x6D, 0x4D, 0x3D, 0x71, 0x92, 0x9C, 0xE5, 0x32, 0x10, 0xB9}[counter];
break;
case 0x126: // HCA_01 Heading Control Assist
crc ^= (uint8_t[]){0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA, 0xDA}[counter];
break;
case 0x12B: // GRA_ACC_01 Steering wheel controls for ACC
crc ^= (uint8_t[]){0x6A, 0x38, 0xB4, 0x27, 0x22, 0xEF, 0xE1, 0xBB, 0xF8, 0x80, 0x84, 0x49, 0xC7, 0x9E, 0x1E, 0x2B}[counter];
break;
case 0x12E: // ACC_07 Automatic Cruise Control
crc ^= (uint8_t[]){0xF8, 0xE5, 0x97, 0xC9, 0xD6, 0x07, 0x47, 0x21, 0x66, 0xDD, 0xCF, 0x6F, 0xA1, 0x94, 0x74, 0x63}[counter];
break;
case 0x187: // EV_Gearshift "Gear" selection data for EVs with no gearbox
crc ^= (uint8_t[]){0x7F, 0xED, 0x17, 0xC2, 0x7C, 0xEB, 0x44, 0x21, 0x01, 0xFA, 0xDB, 0x15, 0x4A, 0x6B, 0x23, 0x05}[counter];
break;
case 0x30C: // ACC_02 Automatic Cruise Control
crc ^= (uint8_t[]){0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F}[counter];
break;
case 0x30F: // SWA_01 Lane Change Assist (SpurWechselAssistent)
crc ^= (uint8_t[]){0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C}[counter];
break;
case 0x324: // ACC_04 Automatic Cruise Control
crc ^= (uint8_t[]){0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27, 0x27}[counter];
break;
case 0x3C0: // Klemmen_Status_01 ignition and starting status
crc ^= (uint8_t[]){0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3}[counter];
break;
case 0x65D: // ESP_20 Electronic Stability Program
crc ^= (uint8_t[]){0xAC, 0xB3, 0xAB, 0xEB, 0x7A, 0xE1, 0x3B, 0xF7, 0x73, 0xBA, 0x7C, 0x9E, 0x06, 0x5F, 0x02, 0xD9}[counter];
break;
default: // As-yet undefined CAN message, CRC check expected to fail
auto crc_const = crc_mqb_constants.find(address);
if (crc_const != crc_mqb_constants.end()) {
crc ^= crc_const->second[counter];
} else { // As-yet undefined CAN message, CRC check expected to fail
printf("Attempt to CRC check undefined Volkswagen message 0x%02X\n", address);
crc ^= (uint8_t[]){0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}[counter];
break;
}
crc = crc8_lut_8h2f[crc];

crc = crc8_lut_8h2f[crc];
return crc ^ 0xFF; // Return after standard final XOR for CRC8 8H2F/AUTOSAR
}

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