From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grant Edwards Subject: Re: New serial card development Date: Tue, 23 Oct 2012 18:45:51 +0000 (UTC) Message-ID: References: <5074703E.408@commtech-fastcom.com> <20121014093704.GA6207@thunk.org> <20121016002608.64b33de5@pyramind.ukuu.org.uk> <20121016023226.GA17446@thunk.org> <20121019212158.GB4721@thunk.org> <20121023192633.18849645@pyramind.ukuu.org.uk> Return-path: Received: from plane.gmane.org ([80.91.229.3]:51991 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932824Ab2JWSqN (ORCPT ); Tue, 23 Oct 2012 14:46:13 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1TQjUV-00080q-L2 for linux-serial@vger.kernel.org; Tue, 23 Oct 2012 20:46:15 +0200 Received: from dsl.comtrol.com ([64.122.56.22]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 23 Oct 2012 20:46:15 +0200 Received: from grant.b.edwards by dsl.comtrol.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 23 Oct 2012 20:46:15 +0200 Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: linux-serial@vger.kernel.org On 2012-10-23, Alan Cox wrote: >> Can it be guaranteed that it's going to be fast enough at high >> baud-rates to prevent any gap between the first byte and subsequent >> bytes? > > Possibly not for some protocols (or worse yet 'almost always' for > some protocols). > > It's something to look at once the basic bits are in. > >> I now work for a company that has manufactured PC serial boards for >> 25+ years, and we still get regular requests for that feature (and our >> boards do support it -- though our Linux driver does not). > > In which case when we get to addressing this it will be good to make > sure we cover your needs as well. FWIW, in some products we're planning that will require support for various industrial serial protocols, I'm leaning towards abandoning the tty driver approach and writing a stand-alone character device driver. The byte-stream oriented tty/line-discipline layer just doesn't fit well when dealing with frame-oriented industrial protocols that depend on things like 9th bit addressing and detecting sub-millisecond inter-byte timeouts. When I add in the lack of long-term stability in the tty API it seems like it might not be such a bad idea to give up trying to make the tty abstraction fit a use case that's just nothing like a teletype. -- Grant Edwards grant.b.edwards Yow! Gibble, Gobble, we at ACCEPT YOU ... gmail.com