Subject: DEC 3000/300 interrupt handling and serial port speed.
To: None <>
From: Paul Mather <>
List: port-alpha
Date: 04/04/2000 10:09:06
Sorry to harp on about this still, but I know there are quite a few
people on here who know quite a bit about DEC 3000/300 hardware, so I
figure one of these days an answer might pop out... ;-)

Is it possible to drive the alternate console/printer port of the
DEC3000/300 at a speed other than 9600??

I dug out my "DEC 3000 Model 300 Series AXP Hardware Reference
Guide," and in Chapter 6 ("Setting the Alternate Console Feature") it

	"The alternate console/printer port on the back of the system
	unit is set at the factory to the parameter settings listed
	in Table 6-2.  These settings cannot be changed."

Table 6-2 basically states that the port is 9600/8N1.

By "these settings cannot be changed" does it mean that the port is
somehow hard-wired to those settings, or that SRM simply defaults to it
on power-up?

In addition, I notice that under NetBSD, when the alternate
console/printer port is going full steam (e.g., RX/TX to an attached
modem), the number of interrupts on INT 17 and 19 rises to well over
1000/sec, and when it does, the incidences of pppd spew (messages about
bad fcs; exceeded MRU; VJ uncompress failed; bad seq #; etc. [sometimes
even a "silo overflow!"]) into my console rises accordingly.

This makes me wonder: could NetBSD on the DEC 3000/300 handle the
interrupt rate of a serial port set to 57600 or, dare I say it, 115200??

(I know the max rate in /sys/arch/alpha/tc/scc.c is set to 57600; is
this the most the hardware can manage??)




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