BBB CPU clock (was: Re: FreeBSD on Cubieboard 2, UDOO and Galaxy Note 10.1 (Exynos).

[Paul Mather]

On Sep 30, 2013, at 5:04 PM, Jia-Shiun Li <jiashiun at gmail.com> wrote:

> On Mon, Sep 30, 2013 at 11:26 AM, Tim Kientzle <kientzle at freebsd.org> wrote:
>> 
>> My understanding:
>> 
>>  * We should query the PMIC to determine whether we're running from 5V supply or USB.
>> 
>>   * Based on that, we should adjust the CPU clocks.  We should be able to run 1GHz from 5v supply.
>> 
>> Connecting cpufreq would be a nice addition.
> 
> Hi Tim,
> 
> Yes you are right. I digged a bit the PMIC docs.
> I didn't realize that DCDC2/3 output to MPC/core are adjustable.
> 
> The PMIC capped USB input at 500mA by default, so if not changed otherwise,
> or to be safe with what most USB power supplies are, it is correct to only go up
> to 1GHz on DC input.
> 
> I played for a while manually setting PMIC from u-boot prompt, setting MPU volt
> to 1.325v, raise USB current limit, etc. but still cannot get it run
> above 800MHz.
> It always stopped booting at initing uhub. Looks like I need a bigger
> DC adapter.

What 5V adapter are you using?  The one recommended by Adafruit for the BeagleBone Black is a 5V 2A adapter.  The BBB system reference manual states, "A 5VDC supply can be used to provide power to the board. The power supply current depends on how many and what type of add-on boards are connected to the board. For typical use, a 5VDC supply rated at 1A should be sufficient. If heavier use of the expansion headers or USB host port is expected, then a higher current supply will be required."  The BBB Wiki (http://circuitco.com/support/index.php?title=BeagleBoneBlack) lists the power consumption of the BBB itself as 210--460 mA at 5V depending on "activity and processor speed."  I believe if you use capes with the BBB then you need to use the external PSU.

I've personally found the BBB to be a bit flaky when run via the USB OTG connector.  I prefer to run it via a 5V external PSU for stable operation.

Cheers,

Paul.