Rockbox Technical Forums

Rockbox Development => Starting Development and Compiling => Topic started by: DefineByte on July 31, 2007, 08:23:33 AM

Title: Disabling iPod Video CPU Overclocking
Post by: DefineByte on July 31, 2007, 08:23:33 AM
If I wanted to revert the iPod Video boost frequency back to the default 75MHz what changes would I need to make to the source?

Just curious. :)

edit: oops. I think I should have posted this in 'Getting Started and Compiling'. >.>

edit2: Thanks GodEater.
Title: Re: Disabling iPod Video CPU Overclocking
Post by: Llorean on July 31, 2007, 12:46:54 PM
The CPU isn't overclocked. 80mhz is what it's officially designed for.

Why exactly do you want to underclock it?
Title: Re: Disabling iPod Video CPU Overclocking
Post by: DefineByte on July 31, 2007, 02:46:58 PM
Humpf. I was sure it was 75MHz. :-X

Never mind then. xD
Title: Re: Disabling iPod Video CPU Overclocking
Post by: Llorean on July 31, 2007, 02:54:25 PM
Well, the information we have states that the PortalPlayer CPUs are either rated t 80mhz or 100mhz (depending on target). That's one of the few things we actually do know (or at least, think that we do). :)
Title: Re: Disabling iPod Video CPU Overclocking
Post by: DefineByte on July 31, 2007, 03:01:47 PM
I was looking around a few sources and they said 75MHz. Of course I use the term 'sources' in the loosest possible sense, being forum posts etc. It didn't seem right that you were overclocking, I have to admit.
Title: Re: Disabling iPod Video CPU Overclocking
Post by: Llorean on July 31, 2007, 03:06:34 PM
Rockbox isn't going to intentionally run hardware beyond known safe limits. In the one case (that I know of) where something is overclocked, it's the MP3 decoder chip (I believe) on the Archos units, which is overclocked up to double speed when pitch is at 200%, and this has been tested for extremely long runtimes without any ill effects.

But in this case, as far as I know, we're just getting the full use out of the chip that we're supposed to be getting.
Title: Re: Disabling iPod Video CPU Overclocking
Post by: Mad Cow on July 31, 2007, 04:49:46 PM
There was some experimentation with overclocking the ipod video, I remember they guy got it to around 120 mhz before it started crashing. But that's kinda off topic.
Title: Re: Disabling iPod Video CPU Overclocking
Post by: Llorean on July 31, 2007, 04:52:17 PM
Yeah, if I recall he runs his iPod with an unboosted frequency of 60 and a boosted of 90, relatively destroying battery life (there's no real reason to increase the unboosted frequency, it just means more wasted clock cycles when you don't need to be boosted, though it does make the UI a bit more snappy, not a huge concern and something that will improve with dual core).
Title: Re: Disabling iPod Video CPU Overclocking
Post by: Mad Cow on July 31, 2007, 10:59:51 PM
Yeah, if I recall he runs his iPod with an unboosted frequency of 60 and a boosted of 90, relatively destroying battery life (there's no real reason to increase the unboosted frequency, it just means more wasted clock cycles when you don't need to be boosted, though it does make the UI a bit more snappy, not a huge concern and something that will improve with dual core).

The battery difference in minimal in alot of cases, for example the gigabeat gets about 20 minutes more play time with boosting enabled as opposed to running 100% all the time.
Title: Re: Disabling iPod Video CPU Overclocking
Post by: Llorean on July 31, 2007, 11:07:49 PM
The Gigabeat is a unique case, we're not sure the boosting was enabled properly, nor are we sure that the processor doesn't have its own power management features (as far as I know).

Other players have showed significant improvement once CPU scaling is enabled. Please try not to make general statements based off the results on one player.
Title: Re: Disabling iPod Video CPU Overclocking
Post by: mikeage on July 31, 2007, 11:53:26 PM
In earlier versions of Rockbox, the iPod (at least my 4G) ran at 75MHz when boosted.

It now runs at 80MHz. I don't recall exactly when the frequencies were changed.