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Date:      Fri, 11 Feb 2000 18:51:57 +0100
From:      "Jose M. Alcaide" <jose@we.lc.ehu.es>
To:        freebsd-mobile@FreeBSD.org
Subject:   "interrupt-level buffer overflows" with Xircom RealPort Modem 56
Message-ID:  <38A44C3D.6B2B39A6@we.lc.ehu.es>

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Hello,

I have just purchased a Xircom RealPort Modem 56 (PCMCIA). I easily
got it working as sio1 adding an entry to pccard.conf. However,
messages like these appeared on the console while I was testing
the modem from user-ppp (term), typing commands such as "AT&V" or
"ATI11", which give some lines of output:

sio1: 31 more interrupt-level buffer overflows (total 31)
sio1: 273 more interrupt-level buffer overflows (total 273)
sio1: 437 more interrupt-level buffer overflows (total 710)

... and so on.

After reading the sio(4) manpage and briefly examining sio.c, I disabled
the FIFO with sio flags 0x20, and the messages went away. However,
this modem supposedly has (or emulates) a 16550A, which has a 16-byte FIFO.
I also tried sio flags 0x08 (polled output) and 0x08000000 (8-byte FIFO)
to no avail. Only disabling the FIFO works, but this could affect
performance.

The laptop is new, a Dell Inspiron 3700 with a Celeron 433, so that
this is not a CPU speed problem. And a PCMCIA Ethernet card works
fine, so that this is not a general interrupt processing problem.

A final note: I had "AUTO_EOI1" enabled in the kernel, but removing it
did not make any effect on the buffer overflows.

Any ideas? Is anyone using other similar Xircom modems, and having this
same problem?

Thanks,
-- JMA
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José Mª Alcaide                         | mailto:jose@we.lc.ehu.es
Universidad del País Vasco              | mailto:jmas@FreeBSD.org
Dpto. de Electricidad y Electrónica     | http://www.we.lc.ehu.es/~jose
Facultad de Ciencias - Campus de Lejona | Tel.:  +34-946012479
48940 Lejona (Vizcaya) - SPAIN          | Fax:   +34-946013071
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 "Beware of Programmers who carry screwdrivers"  --  Leonard Brandwein


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