[OpenBIOS] About udelay

Mark Cave-Ayland mark.cave-ayland at ilande.co.uk
Sat May 4 00:07:24 CEST 2013

On 03/05/13 22:54, Lennart Sorensen wrote:

>> I see that you used a loop to simulate a wait time. I think there must be a better way of doing it. Doesn't the Sparc emulator have access to a hardware clock that we can use instead of a loop?
> I would have thought the compiler was allowed to optimize away a loop
> that incremented something that noone ever looks at.  It doesn't do
> anything after all.

Fortunately the use of the "volatile" quantifier in the patch makes sure 
that this doesn't happen. Both myself and Artyom have tested the patch 
and it works for both of us, so I'm reasonably confident.

The reason that the udelay() implementation is a trivial one is because 
we need something simple in order to get a working OpenBIOS (and 
hopefully 1.1 release) into QEMU git master in time for feature freeze 
on Monday. If anyone else would like to investigate using timers for 
udelay() on SPARC32/64, I'd be very happy to accept patches from next 
week onwards.



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