Re: Severe deadlock issues with 5.0/MP

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

>> - If I type too fast or paste things into the serial console window
>> (which I am accessing over ssh), lots of characters simply vanish,
>> or are distorted.  Anyone seen anything similar?
> AFAIK: The serial interface of older, SBus era machines has no
> hardware FIFO, or a very short FIFO.

Yes.  The 8530 has basically no FIFO.  It has a received-character
register which can hold a character while another is being received,
and perhaps one more register's worth of buffering, but that's it.
This is why kernels for machines that use it tend to use a two-level
interrupt scheme, with the hardware interrupt very cheaply moving the
data and status to a relatively large ring buffer and scheduling a
software interrupt to do the real work.

> So it is normal that they [lose] characters if they come in too fast.
> I saw the same effect on my SBus machines.

Yes.  But "type too fast" doesn't qualify.  What's a very fast typist?
200 wpm is surely over the top.  That's 1000 chars/minute, or 16
chars/sec (I type faster than most and I'd have trouble typing 16
keystrokes a second even without caring what keys I struck).  If the
kernel takes over 1/16 of a second to field the interrupt and move the
received byte to the ring buffer, something's seriously busted.

Pasting things into a window running a serial comm program, on the
other hand, should be able to run at the rate of the serial line; at
that sort of data rate, dropouts are no surprise unless the line is
running at very slow speeds (like 300 baud).

> Regarding serial break and ddb(4): There may be a sysctl(8) to enable
> / disable ddb(4) upon break.

ddb.fromconsole, I think it is, to control whether ddb can be entered
from the console (whatever that means for the console in use - a break
condition on most serial consoles, L1-A on a Sun keyboard, Ctl-Alt-Esc
on peecees, etc).

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