Re: beaglebone: changing cpu frequency

[Radoslaw Kujawa <radoslaw.kujawa%c0ff33.net@localhost>]

On 3 Aug 2013, at 9:04 PM, Manuel Bouyer <bouyer%antioche.eu.org@localhost> 
wrote:

> On Sat, Aug 03, 2013 at 02:33:17PM -0400, Dennis Ferguson wrote:
>> [...]
>>> 
>>> Note that USB only guarantees 100ma. For highter currents, the device
>>> has to request it explicitely (and I'm not sure the BB does request it),
>>> and the host is free to refuse it.
>> 
>> This is very true if the thing powering the USB port is in fact a host or 
>> hub, and
>> not a power supply, but I think the only way to run that processor on less 
>> than
>> 0.5W at any frequency is to leave the SDRAM and flash turned off and it 
>> clearly
>> couldn't boot an operating system that way.
> 
> Reading the beaglebone manual again, it assume 500ma from the USB port
> (and runs fine from USB power from my host), so it's probably safe to
> assume 500Ma from USB in this case (on the beaglebone it's probably the
> onboard hub which requests 500ma to the host. I don't know for the bb black).

Indeed, the host reports BB as using up to 500mA, however the BeagleBone 
firmware configures TPS65217 to limit current to 1300mA when using an USB power 
source. 

Currently the tps65217pmic driver does not touch this setting at all, merely 
reports it during the boot process, but this is confusing.

-- 
Best regards,
Radoslaw Kujawa