From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:6f8:1178:4:290:27ff:fe1d:cc33]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1Z4Mh6-000456-Mo for barebox@lists.infradead.org; Mon, 15 Jun 2015 05:12:25 +0000 Date: Mon, 15 Jun 2015 07:12:02 +0200 From: Sascha Hauer Message-ID: <20150615051202.GJ6325@pengutronix.de> References: <1434005650-28131-1-git-send-email-s.hauer@pengutronix.de> <1434005650-28131-2-git-send-email-s.hauer@pengutronix.de> <87bngli13j.fsf@dell.be.48ers.dk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87bngli13j.fsf@dell.be.48ers.dk> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH 1/4] Add Reliable Asynchronous Transfer Protocol To: Peter Korsgaard Cc: Barebox List On Fri, Jun 12, 2015 at 02:05:04PM +0200, Peter Korsgaard wrote: > >>>>> "Sascha" == Sascha Hauer 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 -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox