UART device driver (Was: [9fans] random moving of cursor arrow)

[Lucio De Re <lucio@proxima.alt.za>]

On Fri, Jul 25, 2003 at 10:08:08AM -0400, Scott Schwartz wrote:
>
> When doing a pull over ppp, eia1status reports lots of overruns.  Watching
> the modem lights it looks like CS is always lit (not so under linux.)
> So I think something is not quite right in the uart driver.

There's been a rewrite since 3rd Ed (you may recall lack of serial
mouse support when 4th Ed was first released), and I had already
noted bad mouse response on an AMD 586 wanna-be, but recently a
faster CPU started showing signs of stress.  At a glance, the
interupt handler does not seem bloated, but I haven't had a chance
to compare different versions.

I understand this is Presotto territory so we may have to wait for
his return.  I'll have alook around in the meantime, the 8250 is
one chip I understood pretty well in my day.  The FIFO adds a little
complexity I have not yet explored, but I don't think it's excessive.

I have a vested interest, anyway: I have a six-port BOCA card with
the most creative way of mapping its six ports to the I/O and
interrupt space and I'd like some suggestions on representing this
in plan9.ini.

For each port, I can specify one of two addresses, where the first
four may map to the conventional 3F8, 2F8, 3E8 and 2E8 of COM1, 2,
3 and 4 of yore.  3E0 and 2E0 are the options for the last two.
The alternatives are 220, 228, 240, 248, 260, 268 (all hex, of
course).

I think I can disable a port by leaving out the corresponding
jumper, too.

Then for each port I have a choice of IRQ 4, 3, 10, 11, 12 and 15,
respectively, or I can choose SHARED for any or all of them.
Shared, in turn, can be IRQ 4 or 5.

I'm looking for a way to indicate each of these options in plan9.ini,
keeping in mind that I may want to use the default eia0 and eia1
(I don't know how far these stretch, given that on the original PC
COM3 and COM4 uncomfortably shared IRQ$ and IRQ3 with COM1 and
COM2, respectively).

I thought of a six-character string like 112200 with 1 for IOP
option 1, 2 for option 2 and 0 for disabled, but it's ugly and
still does not help with shared IRQs.

I won't mind using six description lines, but I don't know the
plan9.ini syntax scanner well enough to implement such a thing
without some advice.

++L

PS: One last question, how would I handle a USB modem?  Will I have
to provide my own support?