Re: Raspberry Pi 3?


Jeremy McDermond <mcdermj@...>
 

On Mar 10, 2016, at 4:39 AM, 'John Wiseman' john.wiseman@... [UniversalDigitalRadio] <UniversalDigitalRadio@yahoogroups.com> wrote:

The problem is that on the Pi3 the GPU clock frequency can vary, unless it
is locked to 250 MHz, then reducing performance.
Alright. Thanks for being patient and helping me understand the problem, John. I figured there was something I was missing.

The unfortunate thing is that it appears as though they’re doing the frequency scaling in the firmware, so the Linux kernel is not aware of it and won’t be able to correct for the clock changes in the UART driver. It’s also too bad that Broadcom threw this in the “aux” stuff. Apparently they added that module as an afterthought at the end (it also has the other two SPI busses in it) and the hardware isn’t really well thought out. It would certainly be more useful if it were on a clock mux like the rest of the clocks.

Apparently there is another tradeoff, though. If you set force_turbo=1, you’ll cause the GPU core to max clock rate and it will only reduce it in the event of low voltage or thermal issues. This should allow you to have full speed on the GPU along with a functional Mini-UART. The issue here is going to be power consumption and heat. I’ll be checking some of this out when I get hardware to do so.

I think the “official party line” from NWDR is that you should use the device tree overlay to disable bluetooth and restore the AMBA UART to the PiDv.

There is a load of stuff about this on the PI forums.
That’s part of why I didn’t see it. I’m not a big fan of web forums because they’re really a “pull” content system where I have to check different forums by hand, rather than an e-mail list that’s “push” in that it shows up in my central e-mail box. They do have an RSS/Atom feed, though, so I put it in my RSS reader so that I’ll hopefully stay better up to date with this stuff. I’m on one of the RPi kernel wonk’s list but I didn’t see anything about that there yet. I’ll be watching both for possible solutions and will let people know if there ends up being one.

73, John
--
Jeremy McDermond (NH6Z)
Xenotropic Systems
mcdermj@...

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