Axp-List Archive
Re: Boot sequence

Subject: Re: Boot sequence
From: Hannes Reinecke (civhr@civ.hw.ac.uk)
Date: Mon Jul 10 02:39:30 2000


bryan@ak.net wrote:
>
> My guess, based on x86 PCs, would be that once the alpha's firmware
> gets linux running, it's out of the picture, like the BIOS on x86s.
> But I'm confused by the thread which suggests a connection between
> SRM and linux sound drivers. Once the kernel is loaded, can't it
> deal with hardware on its own?
>
Sort of. Some instructions (e.g. interrupts, context swapping etc.)
cannot be executed directly but rather within a special context. This
abstract layer is the so--called 'Privileged Architecture Library' and
it is accessible _always_, not only during boot-time.
A different story is the SRM, which is a console interface for the PAL
code, and this is accessible only during boot. Indeed, it is used for
booting :-).
And this is also the main difference between MILO and SRM: if a machine
check (i.e. hardware fault of sorts) occurs, the machine will just dump
you to the console in the case of SRM, whereas it will attempt to reboot
with MILO/AlphaBIOS (since there is no console to switch to).

> Ah, maybe I can answer my own question -- I think I remember that
> the firmware passes the kernel a list of the devices in the system.
> Is that right? If so, then linux would be unable to use any
> hardware not recognized by the firmware. Is that right?
>
Again, sort of. Linux can only _boot_ from devices recognised at
startup. Once the kernel is started, it does it own device detection.

HTH,

Hannes

-- 
Hannes Reinecke                                 <civhr@civ.hw.ac.uk>
Fluid Loading and Instrumentation Center  Tel: (+44) 131 449 5111 x4456
Dept. of Civil & Offshore Engineering           Fax: (+44) 131 451 3154
Heriot Watt University, Edinburgh EH14 4AS

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