Rene Herman wrote:
On 17-12-07 03:05, H. Peter Anvin wrote:
Incidentally, I had the thought earlier today that port 0xf0 might be
a suitable delay port. It is used only by the 387-emulating-a-287
hack for IRQ 13, which Linux doesn't use on 486+.
[EMAIL PROTECTED]:~/src/port80$ su -c ./port80
cycles: out 2400, in 2400
[EMAIL PROTECTED]:~/src/port80$ su -c ./portf0
cycles: out 2400, in 2400
(Duron 1300)
I suppose you mean using it instead of port 0x80 always and not just as
an alternate port? For the latter 0xed is alright I guess...
FWIW, the criterion used in the kernel for when to use IRQ 13 is:
/*
* External FPU? Set up irq13 if so, for
* original braindamaged IBM FERR coupling.
*/
if (boot_cpu_data.hard_math && !cpu_has_fpu)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
setup_irq(FPU_IRQ, &fpu_irq);
In that case we can't actually use port 0xF0 (it is, however, safe to
use it during setup, specifically before we can take our first FPU
exception.)
-hpa
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