Date: Mon, 12 Jul 2004 20:22:15 +0100 From: Andy Holyer <andyh@hhbb.co.uk> To: "Alex Mitchell" <alex@vestigocorp.com> Cc: freebsd-questions@FreeBSD.org Subject: Re: LRZSZ Message-ID: <C894EC53-D438-11D8-A8CC-000D93511A6A@hhbb.co.uk> In-Reply-To: <FKEJLIBBEDCPHJIAGPPBMEOBGDAA.alex@vestigocorp.com> References: <FKEJLIBBEDCPHJIAGPPBMEOBGDAA.alex@vestigocorp.com>
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On 9 Jul 2004, at 21:55, Alex Mitchell wrote: > > A very large automotive supplier (our client) uses HHP Dolphin 7200 > scanners to scan their automotive crates. The scans are batched in > the scanners. When they are ready to upload the data to our server, > they dock the scanner in the cradle. The cradle is connected to a 56K > US Robotics modem. We wrote the scanner application using 16bit C > compiler (because the scanners are DOS based). We're using a Y-Modem > protocol to upload the data files. The scanner dials into a modem > pool to upload the data. When a connection is established, LRZ is > used to receive the data files from the scanner. With smaller files > (7K and smaller), this works fine. I've tried uploading a 12K file. > After uploading 8K, the scanner returns an NAK error. This error > keeps repeating until the scanner gives up and the upload fails. I've > tried a 24K file, it fails after 16K. I've tried a 56K file and it > fails at 16K. NAK error each time. I've tried the above scenario on > FreeBSD 4.7 and FreeBSD 5.2.1 about 30 times for each file size, with > the exact same result each time. I had a very similar problem about 10 years ago. Macs trying to send mail just hung when they had more than x lines of text. It turned out in the end that the then MacOs TCP/IP stack was ignoring the stated MTU, and just tried to send the whole thing in one huge packet. On dial-up, this overflowed the kernel IO buffer size, and hung the process. In the end I looked at the serial port handling code in the kernel, and the buffer size was sensible for a 1990-era machine with 64MB of ram, being about 1K each. Since we had plenty of RAM on the boxes, I sacrificed a bit by upping the buffer size define to something big (I think 64K), rebuilt the kernel and the problem went away. I wonder if something similar is happening to you? --- Andy Holyer, Technical stuff Hedgehog Broadband, 11 Marlborough Place Brighton BN1 1UB 08451 260895 x 241
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