modem woes / IRQ sharing: 3COM PCI FaxModem

[Rick C. Petty]

After many troubles getting various controllerless modems to work, I
purchased a USRobotics (OEM 2977) controller-based PCI modem.  Under a
GENERIC 5.1-RELEASE kernel, the modem is detected:

sio0: <3COM PCI FaxModem> port 0xb800-0xb807 irq 5 at device 7.0 on pci1
sio0: moving to sio4
sio4: type 16550A

However, attempting ppp(8) or cu(1) causes a partial freeze-- it lets me
swap virtual consoles but I can't type anything except on /dev/ttyv0 (which
I have turned off) nor does the network stack respond to anything beyond a
ping(8).  Some googling suggested that this was a shared IRQ problem.  I
tried using various combinations of the sio(4) flags, and eventually I
arrived at 0x6 (disable FIFO, no AST/4-compatible IRQ control register) and
at boot, the sio4 link changed to:

sio4: type 16550A fifo disabled lookalike with 1 bytes FIFO

and I was able to send one byte before it froze.  I am unsure how to make
the kernel reassign the IRQ for this card, if it even is an IRQ problem,
because it's a PCI card and it's sharing with all the other PCI devices.
BTW, adding the following to /boot/device.hints:

hint.sio.4.flags="6"

didn't work, I actually had to nstead assign it to sio0 before it would
recognize the flags option...  the problem is that I cannot totally
disable the sio0 device because I need it for the touchscreen in X, and I
can't figure out how to trick sio(4) to use the flags for sio4 only!

Any suggestions on how to get this modem to work and/or to remap the IRQ or
anything of the sort?  FYI, I had difficulty getting the same hardware to
work in windoze-- after manually installing the .INI the modem wouldn't
query until I disabled the use of FIFO buffers, suggesting this modem
doesn't have a 16550-compatible UART.

There's a linux "driver" which is just a binary to configure the serial
port, but I couldn't get it to run because it requires
/compat/linux/proc/bus/pci/devices which linprocfs(5) doesn't support..

-- Rick C. Petty        Senior Software Engineer, KIWI Computer
---------------------------------------------------------------
rick at kiwi-computer.com            http://www.kiwi-computer.com/