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I've got what appears to be a generic 8-bit 2-port serial card; both
UARTs are 16550's. I/O over the first port (COM1:, or /dev/cua0)
works wonderfully - I/O over the second port (COM2:, or /dev/cua1)
is excruciatingly slow. This behavior occurs whether I'm trying to
log in at a prompt from agetty, or if I do a "cu -l /dev/cua1" and
send commands to the modem. Sending "ATZ" to the modem via /dev/cua0
gets me an "OK" immediately - sending "ATZ" to the same modem via
/dev/cua1 will get me an "OK" in 3-4 seconds. (The RD light on the
modem makes it appear that outbound characters go immediately.) As
you can imagine, the port isn't very useful to me in its current state.
I've tried swapping in a new 16550 and it didn't make a bit of
difference. I've also tried configuring the kernel for automatic
serial port configuration, or for manual configuration - and there
are no cards in the machine which conflict with the IRQ (IRQ 3).
I've looked through the docs and the source and the Serial-HOWTO,
but haven't seen anything that gives me any ideas. Has anyone else
experienced this? Is it a know bug? (Kernel is 1.0, from a Slackware
distribution with other bits tacked on. :)
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"Over 2MB of news are posted each day. This is a staggering figure
when you consider that most news feeds are run over 1200 baud modems."
- Nemeth, et al, "Unix System Administration Handbook" (1989)