[Letux-kernel] 1.5GHz problems

H. Nikolaus Schaller hns at goldelico.com
Tue Aug 2 10:24:02 CEST 2016


> Am 02.08.2016 um 09:52 schrieb Matthijs van Duin <matthijsvanduin at gmail.com>:
> On 2 August 2016 at 08:45, H. Nikolaus Schaller <hns at goldelico.com> wrote:
>> So they should be modified dynamically when switching CPU frequencies?
> Yes, and the datasheet seems quite emphatic about it. See section
> 4.2.1 of the omap5 TRM and the large note at the end of section 4.3.2
> (Operating Performance Points -> MPU) of the omap5432 datasheet.
> (Random side note: the same restriction apparently applies to
> AM57xx/DRA7xx based on section 4.2.1 of its TRM, although it's not
> waved in your face as much as on the omap5.)

Ok, so it is something that should be more fundamentally fixed in the kernel.

>> Unfortunately I neither have JTAG equipment nor do we have access to the
>> JTAG interface on the Pyra CPU board. Since neither is needed in normal
>> situations. For a big pile of money we could have built some Pyra CPU
>> boards where these signals are made available on external test points.
> Ouch. You can get a perfectly adequate JTAG debugger (e.g. XDS100v2)
> for less than $100, but not having JTAG pinned out is a problem.

Well, having it pinned out is a space/pcb layout problem...

$100 is not the problem and I have an Openmoko Debug board (which
is also a JTAG debugger).

The problem is the time to set it up (which software to installation) and learn
how to use it appropriately. Like it takes 10 min to buy a pan at some super
market... But learning to cook usually needs more time.

> I read in the TRM that JTAG can alternatively be muxed to the SD card
> slot pins (intended for space-constrained applications like
> smartphones).

Ah yes, I remember. Section 30.2.4 Narrow Interface for Debug and Trace (NIDnT)
has some description - but I have not understood how to enable it before boot or
if that is done automatically.

So we sould need a NIDnT compatible JTAG probe.

> I have no idea however whether that needs any special
> config other than setting the pinmux.

Interesting idea for someone who wants to volunteer to experiment with that.
The setup will be a little tricky since we boot from this SD card but I guess it
is doable.

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