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From devnull@lkml.org Tue Apr 23 14:16:38 2024 Delivery-date: Sat, 20 Jan 2007 16:40:38 +0000 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965297AbXATPl4 (ORCPT ); Sat, 20 Jan 2007 10:41:56 -0500 Received: from miggins.aqhostdns.com ([216.93.243.2]:44282 "EHLO miggins.aqhostdns.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965296AbXATPlz (ORCPT ); Sat, 20 Jan 2007 10:41:55 -0500 X-Greylist: delayed 65064 seconds by postgrey-1.27 at vger.kernel.org; Sat, 20 Jan 2007 10:41:55 EST Received: from cpe-66-68-176-215.austin.res.rr.com ([66.68.176.215]:35426 helo=[192.168.1.100]) by miggins.aqhostdns.com with esmtpsa (SSLv3:RC4-MD5:128) (Exim 4.63) (envelope-from ) id 1H81QU-0003yL-Db for linux-kernel@vger.kernel.org; Fri, 19 J Subject: Serial port blues From: Joe Barr To: Linux Kernel mailing List Content-Type: multipart/mixed; boundary="=-yyTwYkKzxGpZ8FEa4rxS" Date: Fri, 19 Jan 2007 15:37:34 -0600 Message-Id: <1169242654.20402.154.camel@warthawg-desktop> Mime-Version: 1.0 X-Mailer: Evolution 2.8.1 X-Antivirus-Scanner: Scanned and found to be clean by AQHost - http://www.AQHost.com X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - miggins.aqhostdns.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [0 0] / [47 12] X-AntiAbuse: Sender Address Domain - pjprimer.com X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org --=-yyTwYkKzxGpZ8FEa4rxS Content-Type: text/plain Content-Transfer-Encoding: 7bit I'm forwarding this post by the author of a great little program for digital amateur radio on Linux, because I'm curious whether or not the problem he is seeing can be resolved outside the kernel. All comments welcome on/off list. Thanks, Joe Barr K1GPL -- It's a strange world when proprietary software is not worth stealing, but free software is. --=-yyTwYkKzxGpZ8FEa4rxS Content-Disposition: inline Content-Description: Forwarded message - FSK/CW and ioctl jitter / latency Content-Type: message/rfc822 Return-path: Envelope-to: k1gpl@linuxhamshack.org Delivery-date: Fri, 19 Jan 2007 14:33:39 -0500 Received: from warthawg by miggins.aqhostdns.com with local-bsmtp (Exim 4.63) (envelope-from ) id 1H7zUV-00036d-UI for k1gpl@linuxhamshack.org; Fri, 19 Jan 2007 14:33:38 -0500 X-Spam-Checker-Version: SpamAssassin 3.1.7 (2006-10-05) on miggins.aqhostdns.com X-Spam-Level: X-Spam-Status: No, score=-2.2 required=5.0 tests=AWL,BAYES_00 autolearn=ham version=3.1.7 Received: from [68.168.78.211] (port=47980 helo=mta16.adelphia.net) by miggins.aqhostdns.com with esmtp (Exim 4.63) (envelope-from ) id 1H7zUV-000359-Nm for k1gpl@linuxhamshack.org; Fri, 19 Jan 2007 14:33:35 -0500 Received: from [192.168.2.51] (really [24.126.19.211]) by mta16.adelphia.net (InterMail vM.6.01.05.04 201-2131-123-105-20051025) with ESMTP id <20070119191640.SDAU2311.mta16.adelphia.net@[192.168.2.51]>; Fri, 19 Jan 2007 14:16:40 -0500 Message-ID: <45B11CEC.4080806@w1hkj.com> Date: Fri, 19 Jan 2007 14:33:00 -0500 From: w1hkj User-Agent: Mozilla Thunderbird 1.0.6 (X11/20050716) X-Accept-Language: en-us, en MIME-Version: 1.0 To: David , Dave Cooper , Phil Moore , jhaynesatalumni , David Karipides , Walter Fey , edw3nr , Mike Phipps , Rick Kunath , Brett Owen Rees VK2TMG , David Quental , =?ISO-8859-1?Q?P=E4r_Crusefalk?= , PA0R , Bob Christenson , Joe Barr , Joe Veldhuis , Diane Bruce , Walter Giovanni Subject: FSK/CW and ioctl jitter / latency Content-Type: text/plain; charset=ISO-8859-1; format=flowed X-Antivirus-Scanner: Scanned and found to be clean by AQHost - http://www.AQHost.com Content-Transfer-Encoding: 7bit I've spent the last day staring at the oscilloscope and pins RTS and DTR on the serial output for 4 different computers running 4 different versions of Linux. Also have exhausted the search on the internet for information regarding both the latency and jitter associated with ioctl calls to the serial driver (both ttyS and ttyUSB). I'm sure it is out there somewhere, I just cannot find it. I am now convinced that the current serial port drivers available to us on the Linux platform WILL NOT support CW and/or RTTY that is software generated in a satisfactory manner. To test the latency and jitter of the ioctl calls to set or clear RTS and / or DTR I built a basic square wave generator with microsecond timing precision. The timing could be derived either from the select system call or by controlled i/o to the sound card. Both provide very precise timing of the program loop. Each time through the loop either the RTS/DTR was set or cleared. The timing jitter for each 1/2 cycle was from 0 to +4 msec. This varied between systems as each had different cpu clock rates. The jitter is caused by the asynchronous response of the kernel to the request to control the port. ioctl requests apparantly do not have a very high priority for the kernel. They are probably just serviced by a first-in first-out interrupt service request loop. That type of jitter is tolerable up to about 20 wpm CW. It totally wipes out the ability to generate an FSK signal on the DTR or RTS pin. Direct access to the serial port(s) is a kernel perogative in Linux. Only kernel level drivers are allowed such port access. So ... bottom line is that all of my attempts over the past couple of months to provide CW and / or FSK output signal have been to fraught with pitfalls. The CW seems OK for slow speed keying, but the FSK seems impossible to achieve. The FSK using the UART is also limited by the Linux operating system and the current drivers. That limitation excludes the use of 45 or 56 baud BAUDOT. Until such time as new information becomes available I am going to comment out all references to CW and / or FSK via RTS/DTR. I also question how useful the FSK on TxD (UART derived) might be to most users since the 45.45 baudrate is not available in the serial port driver. That function will also be commented out. All this should not really come as a surprise since Linux is not a real-time operating system. By the way, I did try the tests with the test program running with nice -20. Not much difference. Sorry folks, but we win some and lose some. 73, Dave, W1HKJ --=-yyTwYkKzxGpZ8FEa4rxS-- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/