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DS development > DS Arm7 & Arm9 System Clock

#135348 - kiwi.ds - Sun Jul 22, 2007 4:59 pm

I want to know the Arm7 system clock frequency.

Having searched some threads in this forum, such as this:

http://forum.gbadev.org/viewtopic.php?t=5983&start=0&postdays=0&postorder=asc&highlight=system+clock

It seems that both Arm9 and Arm7 system clocks share the same frequency (around 2^25 = 33.55MHz).

The DSTek said "
Quote:
Same as GBA, except F = 33.514 MHz (for ARM9 at least).


So is it true that the Arm7 system clock has a frequency of ~33.55MHz (Not in GBA mode)? Thanks.

EDIT: Does it also means that the Arm7's TimerX will be incremented everytime when its system clock is incremented (assume the prescalar is F/1)
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#135354 - Lick - Sun Jul 22, 2007 6:10 pm

Clockspeeds: 33Mhz (ARM7) and 67Mhz (ARM9).
Timerclocks: 33Mhz and 33Mhz.
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#135355 - kiwi.ds - Sun Jul 22, 2007 6:24 pm

thanks Lick, your answer is very helpful
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#135432 - kiwi.ds - Mon Jul 23, 2007 9:14 am

One more question
Is there any source to tell the more precise value of the timer clock's frequency? (instead of just 33MHz, or 33.5MHz)
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#135433 - Lick - Mon Jul 23, 2007 9:18 am

I just stick to 2^25 normally. But I believe it varies with the hardware.
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#135435 - masscat - Mon Jul 23, 2007 10:09 am

According to gbatek the system clock frequency is 33.513982 MHz. If you use 2^25 then you will have an error of about 0.12% (~2mins if timing 24hours). Depending on what you are doing that may or may not be important.
Using 0x2000000 (2^25) instead of 0x1FF61FE (33.514MHz) may make time calculations nicer.

The frequency of 33.513982 MHz will vary between DSs within the specification of the frequency source. The frequency of the source will also vary with temperature (again within the spec of the source). What these specs are I do not know but should not be anything to worry about.

#135436 - kiwi.ds - Mon Jul 23, 2007 10:30 am

Thanks Lick & masscat.

( I didn't notice the gbatek has DS Various section :P )
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