Re: MacPPC serial ports in 4.0.1 - not quite

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> I could tell from the lights on the modem that the data was going
> out, and that the responses were coming in from the modem, but the
> data never shows up on reads from the device.  [...]

> Oddly enough, when this happened, the "top" display began to show
> about 20% user CPU usage, when there was absolutely no excuse for it
> that I could find.  I'm theorizing that whatever got confused in the
> kernel to "lose" the incoming serial data may also have messed up the
> CPU accounting stats.  This may or may not be related.

To me, this sounds as though the driver went wonky (perhaps due to the
hardware not behaving the way the driver expects) and started waking up
userland as though there were data available when there actually was
nothing.  This strikes me as substantially more likely than the CPU
state accounting getting borked in such a peculiar way.

This does assume that userland is using select()/poll() to prompt read
attempts on the serial line, rather than (say) forking a process which
does a blocking read, but that seems likely given what you've said
about the userland code.

It's reminiscent of my own experiences with macppc serial; I found that
if I used the serial line for anything substantial it would wedge in
some way.  That machine seems to have stopped working, though, and for
the next week I'm in the wrong city to investigate.  My macppc issues
were with 1.4T, which seems to point towards it being something very
long-standing.

/~\ The ASCII                             Mouse
\ / Ribbon Campaign
 X  Against HTML                mouse%rodents-montreal.org@localhost
/ \ Email!           7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B