nRF8002 - CRC calculation for configuration file

Question

Hi, 
 i have a question relative to the configuration tool File Format. 
 I'd like to modify (automatically) the configuration file in order to change the "Device Name" field and customize it for each product before to record configuration in OTP. 
 I tried to do this with a basic text editor and then flash the configuration file.
However, in that case the CRC calculation falls into error... 
 Is it possible to detail the CRC calculation made in order to generate a new valid CRC after file modification ?? 
 Best Regards,

run_ar · Accepted Answer

The nRF8002 uses CRC-16-CCITT, this covers the packet header and data.

A Command Frame is built up like this:
Name, Size, Description
Header
Length, 1, Packet length excluding itself
SeqNo, 1, Sequence number
Data
CfgData, 0..60, Serialized configuration data
CRC
CRC, 2, CRC-16-CCITT covering header and data

uint16_t crcproduct = 0x0000, data_len = 0x0000;
uint16_t crc = 0xffff;

uint16_t crc_16_ccitt(uint16_t crc, uint8_t * data_in, uint16_t data_len)
{
  uint16_t i;

  for(i = 0; i < data_len; i++)
  {
    crc  = (unsigned char)(crc >> 8) | (crc << 8);
    crc ^= data_in[i];
    crc ^= (unsigned char)(crc & 0xff) >> 4;
    crc ^= (crc << 8) << 4;
    crc ^= ((crc & 0xff) << 4) << 1;
  }
  return crc;
}

data_len = sizeof setup1; //remember to remove the old CRC
crcproduct = crc_16_ccitt(crc, &setup1 [0], data_len);