Very nice and short.
It looks like you can recursively call it to build your crc for the entire
message+header.
// Calculate the CRC for the header and message.
crc = sysCRC16(TNC_AX25_HEADER, sizeof(TNC_AX25_HEADER), 0xffff);
crc = sysCRC16(tncBuffer, tncLength, crc ^ 0xffff);
// Save the CRC in the message.
*tncBufferPnt++ = crc & 0xff;
*tncBufferPnt = (crc >> 8) & 0xff;
Could you recursively call it as you aquire the data and build up your
message?
Original Message:
-----------------
From: [EMAIL PROTECTED]
Date: Mon, 5 Dec 2005 09:42:40 -0700 (MST)
To: [EMAIL PROTECTED], discuss-gnuradio@gnu.org
Subject: Re: [Discuss-gnuradio] gmsk error
This is the whole thing. You don't need a lookup table.
/**
* Calculate the CRC-16 CCITT of <b>buffer</b> that is <b>length</b>
bytes long.
* The <b>crc</b> parameter allow the calculation on the CRC on
multiple buffers.
*
* @param buffer Pointer to data buffer.
* @param length number of bytes in data buffer
* @param crc starting value
*
* @return CRC-16 of buffer[0 .. length]
*/
uint16_t sysCRC16(uint8_t *buffer, uint8_t length, uint16_t crc)
{
uint8_t i, bit, value;
for (i = 0; i < length; ++i)
{
value = buffer[i];
for (bit = 0; bit < 8; ++bit)
{
crc ^= (value & 0x01);
crc = ( crc & 0x01 ) ? ( crc >> 1 ) ^ 0x8408 : ( crc >> 1 );
value = value >> 1;
} // END for
} // END for
return crc ^ 0xffff;
}
On Mon, 5 Dec 2005, [EMAIL PROTECTED] wrote:
> On Thu, 1 Dec 2005 16:02:59 -0700 (MST), mgray wrote:
> > The following is a link to CRC16 for the PIC controller with similiar
> > memory limitations:
>
> > http://www.kd7lmo.net/picobeacon_code.html
>
> I looked at the code and all I could find was the function sysCRC16 in
> lines 1899-1916 of the PicoBeacon.c.
>
> I could not find a lookup table. Is there any look up table or is it just
> the codes in the lines I mentioned?
>
> Mike
>
>
>
>
>
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