I am working on a handler for IoT data from an electricity meter which communicates via TTL serial at 115200 baud. It only sends data in packets of less than 1 kbytes every 5-10 seconds.

In order to validate the data I need to check the CRC16 checksum at the end and here is where I don't find a good way to do it...
The application will run on Linux so I checked for operating support but found only sksum, which apparently does not do CRC16.

Is there some package or code available somewhere which can calculate the CRC16 value over a byte array of some 1000 bytes?

In a description of the protocol after showing the data structure it adds this:

crc16 = libscrc.ibm(example_data).to_bytes(2, 'big').hex() >> '7945'

Googling libscrc brings me to Python code on GitHub, which I am not really able to use, never programmed Python...
https://github.com/hex-in/libscrc

Anyone able to help with FPC implementation?

I have found a c++ function that purportedly does CRC16:

unsigned int CRC16(unsigned int crc, unsigned char *buf, int len) {
for (int pos = 0; pos < len; pos++)
{

		crc ^= (unsigned int)buf[pos];    // * XOR byte into least sig. byte of

crc

                                          // * Loop over each bit
        for (int i = 8; i != 0; i--)
        {
            // * If the LSB is set
            if ((crc & 0x0001) != 0)
            {
                // * Shift right and XOR 0xA001
                crc >>= 1;
				crc ^= 0xA001;
			}
            // * Else LSB is not set
            else
                // * Just shift right
                crc >>= 1;
		}
	}
	return crc;

}

Can someone please decode this into pascal?

Is there some package or code available somewhere which can calculate the CRC16 value over a byte array of some 1000 bytes?

http://www.retroarchive.org/swag/CRC/index.html

Hi,

On 2022-10-25 09:30, Bo Berglund via fpc-pascal wrote:

< snip >

Anyone able to help with FPC implementation?

Take a look here,
https://forum.lazarus.freepascal.org/index.php?topic=54791.0

regards,

I couldn't verify the code but it should be  relatively close to your  c++ example. Not sure of the width of int type, I supposed it's 16 bits wide:

function CRC16( crc: Word; buf: PByte; len: Word; Poly:Word=$A001): Word;
var
    pos: Word;
    i: Word;
begin
      for pos:= 0 to len-1
      do
        begin
        crc:= crc xor Word(buf[pos]);    // * XOR byte into least sig. byte of crc
        // * Loop over each bit
        for i:= 8 downto 1
        do
          begin
          // * If the LSB is set
          if ((crc and $0001)  0)
          then
              begin
              // * Shift right and XOR 0xA001
              crc:= crc shr 1;
                 crc:= crc xor Poly;
              end
          // * Else LSB is not set
          else
              // * Just shift right
              crc:= crc shr 1;
          end;
        end;
       Result:= crc;
end;
var
    S: String;
begin
      Readln( S);
      WriteLn( IntToHex( CRC16( 0, PByte(@S[1]), Length(S), $8005), 4));
end.

Il 25/10/22 09:58, Marco Borsari via fpc-pascal ha scritto:

Maybe you'll find this implementation more efficient:

https://gist.github.com/prof7bit/7fc558626f94bd8a81b7

Giuliano

To array of bytes, check this:

https://github.com/fluisgirardi/pascalscada_v0/blob/master/src/scada/crc16utils.pas

There are two routines: one to calculate, another to check if crc16 matches.

Em ter., 25 de out. de 2022 às 08:13, Giuliano Colla via fpc-pascal <