Re: Can't get my PC164 to boot

jestabro@amt.tay1.dec.com
Mon, 25 Nov 1996 22:25:58 +0500

>>> Eric Smith said:
> Jay Estabrook <jestabro@amt.tay1.dec.com> wrote:
> > You can't run a kernel expecting MILO PALcode under SRM PALcode,
> > for example, which is what the "no floppy controllers found" message
> > indicates (actually, what causes that message is that interrupts are being
> > delivered to the kernel in a way the kernel doesn't expect).
>
> Is it really the PALcode that is at fault, or is it that Milo and SRM
> initialize the interrupt controller differently? I was under the impression
> that Milo actually contains and uses the SRM PALcode, but perhaps I'm
> mistaken.

No, MILO does not use SRM PALcode. Only the Evaluation Board PALcode sets
are available as source, which is what the MILOs are built with. And yes,
those boxes that aren't EB's are run with modified EB PALcode, like AVANTI
and MIKASA.

The EB PALcodes are pretty simple, as they don't worry much about
interrupts, expecting the kernel to take care of finding the interrupt
summary registers and dispatching to the appropriate handler. See all the
grotty details in arch/alpha/kernel/irq.c.

When configured for running under SRM console and PALcode, the interrupt
handling of the kernel expects to be told *which* interrupt has occurred.
One can't, unfortunately, use the non-SRM interrupt handling routines, like
alcor_and_xlt_device_interrupt(), when running under SRM, as the interrupt
summary registers have been changed by the SRM PALcode when *it* decodes the
interrupt, and so will no longer indicate the appropriate state. However,
the update_hw() routine needs to know all the grotty details about where the
interrupt registers are, under SRM as well as MILO, to properly manage the
interrupt mask.

Note that the AXPpci33 (NONAME) PALcode built into that MILO, actually
delivers interrupts the same way as SRM PALcode, so the same kernel will
run under MILO and SRM PALcodes.

Someday, get Dave Rusling to explain why its beneficial to have the kernel
know all the interrupt details, as under the EB PALcode.

--Jay++

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American Non Sequitur Society: we don't make sense, but we do like pizza...

Jay A Estabrook Alpha Migration Tools - LINUX Project
Digital Equipment Corp. (508) 952-4202 or (DTN) 227-4202
151 Taylor Street - TAY1-2 enet: jestabro@amt.tay1.dec.com
Littleton, MA 01460-1407 decnet: tallis::jestabro
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