I can also confirm having issues with some off the shelf 5V supplies with the EVM and ended up using a 12V supply. My bench supplies are really clean, maybe I'll run a few experiments.

On Sat, Sep 17, 2016 at 11:35 AM, Tony Lindgren <tony@atomide.com> wrote:
* Michael Mrozek <EvilDragon@openpandora.org> [160917 07:35]:
> Am Wed, 14 Sep 2016 13:49:14 -0700 hat Tony Lindgren <tony@atomide.com>
> geschrieben:
>
> Hi Tony and Nikolaus,
>
> okay, I had a little chat with aTc right now, who has a Pyra prototype
> and also has issues booting it with a stock 5V AC adaptor (and without
> battery).
>
> I think we made quite a huge step with that issue.
>
> As mentioned, some users at IRC with the EVM don't have any issues with
> the EVM and more recent kernels.
>
> However, we all switched to using 12V AC adaptors with the EVM, as we
> ALWAYS had stability issues with 5V adaptors.
>
> I guess both you and Nikolaus are running your EVM with 5V?
> Then that would be a difference!

Interesting, will need to check the voltage here. I've been slowly
rearranging the devices in my rack and it certainly is possible that
I've moved my omap5-uevm from 12V input to a 5V input source around
May or so.

> aTc found some interesting information about that:
>
> page 19 of omap5432-ref-swcu130.pdf:
> if the input voltage from the jack is below approximately 5.60V, load
> switch U4 is enabled (driving the main 5V power rail DC_5V with the
> jack input), and if it is > 5.60V then load switch U18 is enabled
> (driving the main 5V power rail DC_5V with the SMPS 5V output).
>
> -----------
>
> So that means, if you use 5V, you most probably have U4 enabled whereas
> everyone who runs at 12V has U18 enabled (which uses SMPS 5V output
> instead of direct Jack input).
>
> It seems to be unstable when running directly from jack input.
> The igepv5 doesn't have that issue - so something is different here.
> Could it be that the power is filtered better on the igepv5?

I've always powered igepv5 with 5V input and never had any issues.

> What we've found out on the Pyra is that it runs A LOT more stable with
> a battery. I guess the battery provides a more stable power source than
> some random USB AC adaptor.
>
> So maybe it's a hardware issue of the EVM, which runs unstable whenever
> rail DC_5V is powered directly from the input jack and NOT from SMPS 5V
> output.
>
> It sounds like they forgot to smoothen and filter the power source
> here, so the better your AC adaptor is, the more stable it runs.

That seems like the best explanation so far :)

Tony
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