I've got a 28.8k PC Card modem (Xircom) which uses a proprietary serial
buffering scheme that emulates an 8250 (greatest design oversight to an
otherwise good modem). The port is locked at 115200 LAP-M/v.42bis on a
Pentium 75 but I can only get about 2300 cps on a 28.8k connection
transferring a 330K ZIP files using Z-modem (Statistically an inadequate
sample). No retrain or renegotiation during the sessions. ATI6 at
disconnection reports 28.8k connection. Xircom has told me it usually
maxes out in the lab at 2900 cps using the above parameters. They blame
the 8250 emulation but also say they're working on the v.42bis side of
things.

Does the 8250 affect transfer speed in a single tasking environment on a
Pentium 75 with a locked baud rate of 115200? 2900 cps is pretty
disgraceful. What would contribute to this? Does it have anything to do
with the lack of support for DMA access under the current PCMCIA 2.1
standard?

nb: The Xircom's serial buffering is proprietary with the computer side
seeing the UART as an 8250. I can easily multitask under Win95 with
either Windows or DOS comms running without any data loss, serial
overruns etc.


mslim{at}ne.com.au


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