Re: [Gumstix-users] Can anyone confirm or deny the existence of the GPU clock divider?

[Jeff D. <je...@gr...>]

On 12/21/2010 2:26 PM, Darren wrote:
> I read somewhere (can't find it now) that there is a clock divider for the power
> VR SGX that's set to 2, essentially cutting GPU performance in half by default.
>
> Can anyone verify if this is true or not?  And if so how to set the clock
> divider to be faster?

Yes, that is the power-on default.  Something has to set the register to get 
it to full speed.  You used to have to use the devmem2 tool to set it 
yourself, which was eventually added to the rc.pvr script 
(/etc/init.d/pvr-init) in openembedded.  I think the newer SGX drivers do it 
for you.

This is from an old pvr-init script:

         # Set SGX to full speed
         devmem2 0x48004b40 w 0

You could read the register after boot (and maybe only after running some 3D 
graphics) to see if something is already setting it.

> Also can anyone shed any light on the actual CPU speed of the overo Fire and if
> it's safe to run at higher speeds?  Is the Fire a 500, 600 or 720 MHz part?
>   I've run a 600 and 720 with no problems so far, but was wondering if I need to
> do anything like use a heatsink when running at faster than 500?

The web site sells them as 600 MHz.  I don't think there's any way to tell 
what the part is rated for.  600 used to be (still is?) considered mild 
overclocking.

-- 
Jeff DeFouw <je...@gr...>
Programmer
Grand Rapids Technologies