I've been experiencing random ppp hangs while running ppp over a 28.8k
modem line.  I finally managed to track this down to some degree.

Particulars of hardware:
CPU: Am486DX2 66MHz
RAM: 16MB
serial port: 82450(8250 clone?) UART (no fifo)
local modem: motorola premier 33.6

With much rooting around with kgdb and ddb, I discovered that bashing
the TS_BUSY bit in the t_state field of the tty that the modem is on
suddenly un-wedges the serial line.  I haven't yet bothered to trace
it farther, but (yowch... wedged as I was typing this) it seems that
something in the com driver is failing to clear that bit when it
should.

BTW, how come kgdb won't let you write to kernel memory?  Or set
breakpoints? :-)

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