On Fri, Jun 12, 2015 at 02:05:04PM +0200, Peter Korsgaard wrote:
> >>>>> "Sascha" == Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> writes:
>
> > This patch adds support for Reliable Asynchronous Transfer Protocol (RATP)
> > as described in RFC916.
>
> > Communication over RS232 is often unreliable as characters are lost or
> > misinterpreted. This protocol allows for a reliable packet based communication
> > over serial lines.
>
> > The implementation simply follows the state machine described in the RFC text.
>
> Almost ;)
>
> > +static int ratp_recv_pkt_data(struct ratp *ratp, void *data, uint8_t len,
> > + int poll_timeout_ms)
> > +{
> > + uint16_t crc_expect, crc_read;
> > + int ret, i;
> > +
> > + for (i = 0; i < len + 2; i++) {
> > + ret = ratp_getc(ratp, data + i, poll_timeout_ms);
> > + if (ret < 0)
> > + return ret;
> > + }
> > +
> > + crc_expect = cyg_crc16(data, len);
>
> Why crc16? RFC916 states that the checksum is the inverted 1s complement
> 16bit sum, E.G. like TCP/UDP/IP header checksums:
Indeed CRC16 is not correct here according to RFC916. We can implement
the original checksum algorithm, I'm not sure if that's a good idea
though. Plain checksumming does not detect lost 0 characters.
Sascha
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