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SubjectRe: Dreadful xfer rates and TCPv4 bad checksum in 2.1.1xx with PPP
David G Hamblen wrote:
>
> Responding to my own post, I've got a little more info. I borrowed a
> Gateway Telepath xjack pcmcia 33.6 fax/modem, and it works fine at 33.6K.
> Conclusion: something about my serial port (16450) and the serial driver
> is garbling data. The internal modem on COM2 and the Hayes modem on COM1
> both give lots of checksum errors and slow transfers at 14.4, while the
> pcmcia modem works well.

If it's a 16450, that's your problem. you need a 16550(a) to reliably
handle speeds above 9600 bps. The '450 doesn't have a FIFO, so an
interrupt is generated for _every_ byte sent/received. This leads to
dropped characters, hence the checksum errors.

--

Brian Gerst

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