Subject: Re: feasible to return from the kernel to OpenFirmware?
To: None <email@example.com>
From: Derek Peschel <firstname.lastname@example.org>
Date: 01/09/2002 18:15:24
On Wed, Jan 09, 2002 at 10:20:05PM -0000, email@example.com wrote:
> | I have OpenFirmware on my machine (PowerMacintosh G4). As I see it,
> | the bootloader (and the kernel, which it chains to) are just gigantic
> | subroutines called by OF. Therefore, the kernel ought to be able to
> | return to OF as the result of some flavor of cpu_reboot, with things
> | set up so that I could continue using OF (all CLAIMed memory freed,
> | etc.)
> Sure. When you halt a SPARC it returns to the firmware. However,
> if you try to boot some other kernel, the firmware is intelligent and
> resets itself. So in theory there's no reason you couldn't at least
> return to the `ok' prompt.
> In practice, the kernel has probably changed the configuration of
> important devices, so the firmware may not be able to deal with that.
The Sparc code contains various functions (I forget the order in which
they call each other; I'm still using MacOS for networking):
and on OpenFirmware machines, one of them eventually calls OF_exit
and assumes it won't return. The MacOS code also has OF_exit but
assumes it might return (thus the endless loop I mentioned). So
I think the Mac implementation of OF is conspiring against me.
Do you know how the firmware knows to reset itself?