[parisc-linux] [prumpf@jcsbs.lanobis.de: temporary registers]

[Phil Schwan <pschwan@thepuffingroup.com>]

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This mail was sent while I was moving the mailing lists to their new
home.  I apologise for the delay.

-Phil

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From: Philipp Rumpf <prumpf@jcsbs.lanobis.de>
To: parisc-linux@thepuffingroup.com
Subject: temporary registers
Date: Thu, 29 Apr 1999 16:50:05 +0000
Message-ID: <19990429165005.06165@insula.local>

I am currently trying to get basic kernel stuff for the pa1.1 port to work.
We have 6 temporary registers that are read/writable by PL0-code only. I
think we should use them to save commonly used values to have them ready
in interrupt handlers.

I propose to use them in the following way:

CR24 - current, 0 while we are handling an interruption
	current is where the registers' contents are stored when we enter
an interruption handler. We have to set it to some "special value" when we
already use the register save slots in current so we don't overwrite them.
(we can save the registers on the kernel stack in that case).

CR30 - kernel stack pointer, 0 when we are using the kernel stack
	when this is 0, GR30 is the valid kernel stack pointer

CR31 - kernel global pointer

this leaves us 3 more registers to save the registers in to handle inter-
ruptions.

	Philipp