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1  Hardware and U-Boot firmware / Hardware / Re: Underclocking the Sheevaplug on: March 30, 2010, 06:11:33 PM
So far I've worked out that I need to set the following pins to the following values (this will run the ARM SoC at 1000MHz).

a) CPU_CLK Freq Select (a nibble made up of MPP[2],MPP[5],MPP[19] and MPP[10])
     Strapping this to 0x7 will run this clock at 1000MHz.

b) CPU_CLK to DDR_CLK ratio (a nibble made up of MPP[33],NF_ALE,NF_REn and NF_CLE)
     Straping this to 0x8 will set the ratio at 5:1.

c) CPU_CLK to CPU L2 Clock ratio (three bits made up of MPP[3],MPP[12] and NF_WEn)
     I'd strap this to 0x3 to give me a 3:1 ratio.

So this will probably give me the slowest Sheevaplug possible.

Does anyone know the following :-
a) Does the Sheevaplug have a firmware/software method of setting these registers (note that this would have to be implemented in some kind of logic cct controlled external to the Marvell SoC).
b) Alternatively, do these pins exist somewhere on the PCB for me do put a solder blob on?

This is the hardware forum. Lets see how many real hardware people are out there ;-)

Thanks in advance for any info.

Steve
2  Hardware and U-Boot firmware / Hardware / Re: Underclocking the Sheevaplug on: March 30, 2010, 02:43:44 PM
Thanks Mark,

I'm looking at the specs now. Still lost to how I actually set the CPU freq. In days gone by I would change a crystal. Maybe I have to start looking for a resonator!
Hope my surface mount soldering skills are up to scratch ;-)

Actually I do see reference to a PLL locked CPU reference oscillator in the specs you linked to Mark. Might be a good start to see if it can be done in software somehow. If I work it out I will report back, but if anyone has any further hints, please do pass them on!

Thanks again,

Steve.
3  Hardware and U-Boot firmware / Hardware / Re: Guruplug as access point? on: March 29, 2010, 04:44:24 PM
I've got my unit set up with hostapd. Even though iwconfig would bluntly refuse to put my rt73 unit into master mode, hostapd seems able to do it.
I'm using the 802.11 drivers option in hostapd. Might be worth a go if you haven't tried already.




Okay - this seems like an obvious question, but here goes:  the new Guruplug can be set up to be a wireless access point, right? 

I've read that for an access point to work under Linux the wireless chip/drivers have to support master mode.  I'm assuming this is the case with the Guruplug, but a Google search for 88w8786 "master mode" comes up empty.

Also, it doesn't have an antenna - does that mean it has a limited range?


Michael
4  Hardware and U-Boot firmware / Hardware / Underclocking the Sheevaplug on: March 29, 2010, 04:07:08 PM
Hello all,

I've searched high and low, but this info eludes me.
How (if possible) do I underclock the CPU in a SheevaPlug?

I don't need 1.2GHz of grunt in my simple application (off grid, 3g connected web-cam and weather station). I need extra low power and cool running.
If I could get this thing running at 600MHz, I'd be happy. I'd even try a bit lower if I could.
I'm running Debian on it, and the kernel has CPUIdle, etc. enabled, but the current draw is still over 1A @5V. I know I've got a long way to go with techniques such as tickless kernels, etc, but for now I'd like to start by hard-coding the max clock speed if possible.
So, is it possible to underclock these Marvells (pun intended!)?

Really appreciate any hints,

Steve.
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