I am interested in trying to use the LPC824 CRC hardware to calculate the CRC for the Modbus protocol.
I use a 512 byte CRC lookup table for the fastest software calculations but now am using a little slower version that uses only a 16 byte table, all to save on the limited flash. It would be much better to use the hardware somehow and Modbus is a very popular serial protocol used on micro controllers.
I have seen that it may be possible on other hardware CRC blocks such as below
void ModbusSlave::_crc_append(uint8_t* buffer, uint8_t* length)
{
CRC0->GPOLY_ACCESS16BIT.GPOLYL = 0x8005;
CRC0->CTRL = CRC_CTRL_WAS_MASK | CRC_CTRL_TOT(1) | CRC_CTRL_TOTR(1);
CRC0->ACCESS16BIT.DATAL = 0xFFFF;
CRC0->CTRL &= ~CRC_CTRL_WAS_MASK;
for (int i=0; i<(*length); i++) {
CRC0->ACCESS8BIT.DATALL = buffer[i];
}
buffer[*length] = CRC0->ACCESS8BIT.DATALU;
buffer[*length+1] = CRC0->ACCESS8BIT.DATALL;
*length = *length + 2;
}
My feeble attempt to duplicate this does not work
uint16_t CalcModbusChecksum(uint8_t* buffer, uint8_t* length)
{
uint16_t ret;
uint8_t len = *length;
Chip_Clock_EnablePeriphClock(SYSCTL_CLOCK_CRC);
Chip_CRC_SetPoly(CRC_MODE_POLY_CRC32,CRC_MODE_WRDATA_BIT_RVS|CRC_MODE_SUM_BIT_RVS);
Chip_CRC_SetSeed(0x8005);
Chip_CRC_Write16(0xFFFF);
while (len--){
*((uint8_t *)&LPC_CRC->WRDATA32) = *buffer++;
}
ret = (uint16_t)Chip_CRC_Sum();
return ret;
} // CalcModbusChecksum
Any help would be appreciated.
This would be very useful to add in the LPC Open code.
Thanks
