Subject: Re: the prom: to map or not to map
To: None <netbsd-ports@NetBSD.ORG>
From: Jason Brazile <email@example.com>
Date: 06/11/1997 10:09:15
> The OpenFirmware is non-reentrant, too. This is taken care of by the
> OpenFirmware device drivers by disabling interrupts before jumping to the
> firmware routines.
Wow. Its hard to imagine having interrupts disabled during an entire
disk block transfer for instance. But that seems like a very interesting
way to get a port going quickly.
> Now for why this isn't the prom: the firmware, upon startup, copies itself
> from rom to ram (the speicification requires this, but note that OpenFirmware
> on PowerMacs doesn't do it), relocates itself to the ram addresses, and
> then runs from the ram image.
Also very interesting. I guess it allocates its own stack too?
> Even when I get around to use native deivce drivers for all the devices in
> a machine, I will still leave this prom copy in main memory in order to
> allow proper exit from the OS into the prom interpreter (the equivalent
> of L1-A on Suns). On my machine, the prom copy occupies about .5 MB of
> ram, so that isn't enough to worry about (the machine has 64 MB standard).
I see. I guess the alternative would be to only allow entry back to the
firmware on shutdown where you would have to read it back in from rom as
a shutdown hook or something. Certainly for .5 MB and the convenience of
being able to pop into the firmware at any moment this makes the most
Thanks for the info.