Date: Fri, 17 Mar 1995 18:52:32 +1000 From: Bruce Evans <bde@zeta.org.au> To: dufault@hda.com, freebsd-hackers@freefall.cdrom.com Subject: Re: Multiport serial cards Message-ID: <199503170852.SAA12539@godzilla.zeta.org.au>
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>I'm interested in a board that will let me receive continuous data at >28.8 on four ports without any problems. At roughly 300 us per >character that will mean we have to service each port every 4.8 ms with >a 16550, or roughly 1.2 ms per port. (Of course lots of times when >you're in the interrupt you'll be able to to serve more than one port) This is a small load for sio. The overhead using an AST/4 on a DX2/66 should be about 6% for input-only and 4% for output-only plus whatever you protocol handler adds. >I think I should use a board with a large FIFO, which I don't think >any of these have. A 1-char "FIFO" as found on 8250's should be adequate provided you have no bus-hogging devices. sio can handle continuous data in both directions at once at 115.2 on 2 ports (but not 3) on a 486DX/33 with 8250's. The system load for this is about 60% (too high for continuous use). A 486DX2/66 with 16550's can probably handle about 6 times as many ports. Bruce
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