[vmips] Linux almost works...

[Brian R. Gaeke]

And then spake Cable Guy, as follows:
> Could interrupts have anything to do with it, or does Linux use
> polling?  I know you mentioned something about that in the vmips docs.

The Linux "serial console" stuff uses polling, but the normal terminal
driver (used for, e.g., /dev/ttyS0) uses interrupts.

> I would rather stay with the DZ serial stuff since even though it's
> weird, it's brutally simple.  An interrupt on each charatcter.  Using
> the "silo" will get you 64 chars before an interrupt.  I was shocked. 
> It seems very primitive, even for the 70s when this stuff came out.

Easy to implement, though!

> I've gotten it to spit out one more line after the "DZ11 write LPR as
> 1e1b".  It's: "Algorithmics/MIPS FPU Emulator v1.5"
> That's cool, though, because I built my toolchain without FPU support.

This is also a good sign, because the Linux/MIPS kernel will load the FPU
emulator the first time a process tries to use the FPU, and the kernel
doesn't use the FPU, so it must be some other process.

> > > Is it possible to jack in a "serial port emulator" into VMIPS?
> > I'm not entirely sure what you mean here.
> In the bootup messages I notce that ttys00 through ttyS03 are
> registered.

The DZ11 supports 4 serial lines, but only one is emulated by current
versions of VMIPS. 

> I was wondering if there was some way to hook into a
> /dev/tty-something with a terminal emulator program and undertake
> communications with a virtual tty of Linux as exposed by VMIPS. 

You can use Minicom (a Linux serial terminal emulator program) to talk
to a pseudo-terminal, and tell VMIPS to use the pseudo-terminal as the
serial console line for the DZ11.  I got it to work a few times with the
SPIM Console, but I haven't used it much.

You might be interested to know that there's a fledgling interactive mode
that you can bring up in current VMIPS CVS by typing Ctrl-Shift-Minus
at the console. Currently it only lets you run or halt the machine,
or dump the state of the CPU, but it shouldn't be hard to add more
commands in future.

-Brian

-- 
Brian R. Gaeke, brg at dgate.org -- GnuPG encrypted mail gleefully accepted