Date: Fri, 8 Nov 1996 00:00:04 -0800 (PST) From: Bruce Evans <bde@zeta.org.au> To: freebsd-bugs Subject: Re: kern/1976: psm and syscons conflicts have escalated Message-ID: <199611080800.AAA16943@freefall.freebsd.org>
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The following reply was made to PR kern/1976; it has been noted by GNATS.
From: Bruce Evans <bde@zeta.org.au>
To: FreeBSD-gnats-submit@FreeBSD.org, Tor.Egge@idt.ntnu.no
Cc: Subject: Re: kern/1976: psm and syscons conflicts have escalated
Date: Fri, 8 Nov 1996 18:38:44 +1100
>>Fix:
>
> psm interrupt must block clock software interrupt to be able to block
> the keyboard polling.
>
> This might mean that tty_imask must block the clock software
> interrupt :-(
It already does :-) (all h/w interrupts and all splnnn()s block
softclock()).
psmintr() and psm_poll_status() and the keyboard <-> psm interface seem
to be too simple to work. psmintr() assumes that the interrupt is always
for it and that exactly one scancode is delivered. If the configuration
in GENERIC is correct:
1. psm_poll_status() steals keyboard scancodes.
2. Now equality is restored - the syscons timeout routine steals psm
scancodes :-).
3. The different irq for psm is the only thing that separates psm
scancodes from keyboard scancodes. Polling cannot work.
psm_poll_status() tests the magic bits 0x03. 0x01 is KB_BUF_FULL and
0x02 is KB_READY. Actually, psm_poll_status() is not so magic, just
badly written and probably broken. 0x02 is also PSM_OUTPUT_ACK.
psm_poll_status() bogusly reads the input to ack output and loops
forever unless the (ack) input happens to be ready then or interrupts
are bogusly enabled so that an interrupt can clear the input.
4. psm_poll_status() is sometimes (e.g. in psmopen()) used without
blocking tty interrupt. This bug makes the bugs in 1) and 3) less
serious.
Summary: equality isn't quite restored. psm_poll_status() is actually a
broken version of kbd_wait(), and it is only used to issue commands, not
to poll for input, so it only hangs the system sometimes :-]. However,
syscons now polls for input, and this cannot work.
Bruce
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