Re: [OFF-TOPIC] CRC errors & 33.6 3 COM external modem

[peterc@verrine.demon.co.uk (Peter Corlett)]

Person, Roderick <personrp@ccbh.com> wrote:
[...]
> been spending time upgrading hardway. I aquired a 33.6 3Com
> external modem. Quite a boost from my old 14.4...I quess If I did
> get so many F#$ CRC errors.

I found that my USR Courier did exactly the same thing - lots of
suspicious PPP errors which went away if I lowered the port speed to
below 9600. It turned out to be lost interrupts. It sounds like you
have the same problem.

I've seen three culprits for this one:

1) You've got a slow/buggy UART on your I/O card. It should be a
   16550A or better. You can tell what kind you have by running
   "setserial /dev/ttySx" (x for your port numbe) as root. If it says
   8250, 16450, you should buy another one.

2) You have an IRQ conflict. "cat /proc/interrupts", and check
   they're all where you expect them to be. This is quite likely the
   case if your modem is on /dev/ttyS[23] and you've got a lot of
   other cards.

3) The one I've not seen documented elsewhere: hdparm. I originally
   used hdparm on my old 486 to speed up my disk accesses by enabling
   32 bit accesses and multiple mode. Alas, multiple mode hogged the
   bus, so every time I accessed the disk, I'd lose serial
   interrupts. Using "-u1" here fixed this. *WARNING*: some
   motherboards don't like this, like my current Pentium one, and may
   trash the disk (as I discovered the hard way.)

-- 
Peter Corlett, Many-hatted BOFH, tw2.com Limited.
use Standard::Disclaimer qw/Not my employer's opinion/;