Using the LPC11E68 CRC Engine to Calculate HDLC FCS

[Carlos_Mendoza]

Using as base the periph_crc example that comes with LPCOpen the following code can be used to calculate the frame check sequence of a HDLC frame using the LPC11E68 CRC:

 

#define HDLC_FRAME_FCS           0xF0B8         // When correct FCS is included in CRC before the compliment and byte swap.

// Chip_CRC_Use_HDLC()
// Configure the CRC Engine for the CRC used for HDLC FCS.

STATIC INLINE void Chip_CRC_Use_HDLC(void)

{
               LPC_CRC->MODE = MODE_CFG_CCITT | CRC_MODE_WRDATA_BIT_RVS | CRC_MODE_SUM_BIT_RVS;
               LPC_CRC->SEED = CRC_SEED_CCITT;
}

// HdlcCheckFCS()
// Evaluate the HDLC Frame Check Sequence (CRC).
// pBuffer and length refer to the entire frame including the FCS bytes
// after 7E/7D un-byte-stuffing, but not including the start/stop flags.
// Returns true if valid.
// Returns false if not valid.

uint8_t HdlcCheckFCS(uint8_t *pBuffer, uint8_t length)

{

   Chip_CRC_Init();
   Chip_CRC_Use_HDLC();

   uint8_t index = 0;
   uint8_t count = 0;

   while(count++ < length)
   {
      Chip_CRC_Write8(pBuffer[index++]);
   }

   uint32_t sum = Chip_CRC_Sum();

   Chip_CRC_Deinit();

   return sum == HDLC_FRAME_FCS;

}‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The LPCOpen package can be downloaded from this page:

LPCOpen Software for LPC11XX|NXP 

Hope it helps!

Best regards,

Carlos Mendoza