Questions About Cpufreq

[sbock]

I've a few questions about CPUfreq respectively overclocking with the Wiz in general.

So at default state the Wiz CPU is clocked @533 MHz. The RAM runs @133 MHz, so the devider is 4. The memory bandwidth is 533 MByte/sec.

I presume when we raise the CPU frequency the RAM will be overclocked successive.
Most of the Wiz run @800 MHz, so in this case the RAM will be @200 MHz. Now the memory bandwith should be 800 MByte/sec.

-Is this correct?
-So is the performance gain we see when overclocking the Wiz a result of an increased memory bandwith and not first of all more CPU power?

Thoughts and comments are welcome...

Regards,
Stephan

 

[MWeston]

My guess would be that the clocks are derived separately on different PLLs using the main clocks of 12MHz and 27MHz. I don't have access to the datasheets as most people don't but I would imagine 200MHz would never work on 133MHz RAM and that can't be right.

Also, based on the performance numbers seen, it looks to be all just CPU overclocking and not the memory. I think a few people have the datasheet and can clarify this.

 

[Pickle]

Im pretty sure they are separate, I know someone tried messing with the timings, but they are pretty tight as it is and no improvements were made without adding stability problems

 

[notaz]

Yeah the memory is connected to system bus, which is clocked by different PLL. ARM is connected to system bus though it's own bus, and divider of 4 only applies for the ARM bus.

 

[sbock]

Thanks to all the gurus for the answers. So the memory bandwith stays constant during over and under clocking? This means Cpufreq /Pollox works different then the GP2x counterpart. At least according to god_at_hell in the readme of his GP2x tweak tool:

QUOTE
RAM-Divider
Same as CPU-Divider ... it divides the RAM-Clock. The RAM-Clock is the half of the CPU-Sourceclock. If you overclock your CPU, your RAM will be
overclocked too. The used RAM is PC133 RAM, so the maximal frequency specified is 133mhz. This means, if you go over 266mhz CPU clock, the RAM will
run outside it's specifications. Now the divider comes in handy. If you clock your GP2X at 300mhz, your RAM-Clock is 150MHZ. If you now choose a
divider of two, the resulting RAM-Frequency will be 75Mhz. I implemented this in the hope, that I can overclock my GP higher than before, but it
seems, that for me the CPU is the weak part. But if you're unlucky and have a bad RAM-Chip, this could be a solution for a faster CPU.


Do you think there is a possibility to change the memory clock or is the RAM always at its limits?
Is a manipulation af the RAM timings thinkably?

Regards,
Stephan