Date: Thu, 30 Jan 1997 20:40:20 +1100 From: Bruce Evans <bde@zeta.org.au> To: freebsd-hardware@freebsd.org, plm@xs4all.nl Subject: Re: Fast 16550A compatible serial card?? Message-ID: <199701300940.UAA05534@godzilla.zeta.org.au>
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>As cheap alternative to a Hayes ESP someone recommended me a serial >card called T9000+. It contains a 16550A compatible, yet runs at >max. speed of 460k8. > >Is this possible? And is it possible under FreeBSD? 16550A's are specified to work up to 1.5Mbps. Supporting 460.8Kbps properly would require a few changes (it might work modulo some buffer overflows at 460.8Kbps when the software thinks the speed is 115.2Kbps). Expect an ISA bus overhead of 15-20% per port at 46080 cps bidirectional saturated (corresponding to 4-5% at 11520 cps). At 150000 cps, the ISA bus overhead would be 50-65% per port (too large for normal operation) and the fifo trigger level would certainly have to be reduced to avoid silo overflows, and you would need a fast cpu faster than a 486 just to complete the i/o processing in the remaining 50-35% of the time. Bruce
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