Re: raspberry pi zero W serial port overlay fun

[Brad Spencer <brad%anduin.eldar.org@localhost>]

Patrick Welche <prlw1%talktalk.net@localhost> writes:

[snip]

> - replace firmware:
>
>     mount /dev/sd0e /mnt
>     cd /mnt
>     for sfx in elf bin dat; do
>       rm *.${sfx}
>       cp /tmp/firmware/boot/*.${sfx} .
>     done;
>     rm dtb/*
>     cp /tmp/firmware/boot/bcm2708-rpi-zero-w.dtb dtb
>
>   NB in rpi.img.gz was called: bcm2835-rpi-zero-w.dtb, bcm2708, yet
>   dtc -I dtb -O dts  ./boot/overlays/disable-bt.dtbo
>   shows

[snip]


>
> Cheers,
>
> Patrick


Hello...

I really wish it was simpler to tell what was happening with this FDT
stuff...  like really super verbose debugging messsages...

I have the same speed shifting problem on some "Raspberry Pi 3 Model B
Rev 1.2" that you have on the Zero[*].  A third method with the RPI3
that can be used to work around this problem is to set forced_turbo=1 in
/boot/config.txt..  you won't be able to step speed any more, but the
serial port console works.

In an effort to do better than forcing turbo on all of the time I did
the above replacement that your posted about on my RPI3 that exhibits
this speed shifting on the console and all I had to do was replace the
firmware with the upstream version.  The only difference between what
you did and what I did was I included in /boot/dtb ALL of the dtb files
from upstream and did not include /boot/overlays at all.  I can't tell
any differences in dmesg between the two firmware types but the one from
NetBSD clearly exhibits the speed shifting problem while upstream does
not have the problem and allows for the frequency to be changed.  Adding
'dtdebug=1' to /boot/config.txt didn't add any additional messages as to
which DTB file was being used, if any...  I assume that something got
loaded because if I empty out /boot/dtb completely, the system doesn't
boot at all, it seems.

I did other experiements ...  and it seems that just replacing the
*.bin, *.elf and *.dat files and loaders is enough to "fix" this problem
on the RPI3.. that is the NetBSD dtb files (from -current 9.99.99, BTW)
worked fine with the upstream loaders and other files (I assume that is
what the *.bin, *.elf and *.dat stuff is mostly boot loaders).

Both -current and 9.2_STABLE have a working console.






[*] - A complete aside... I have a number of RPI3 systems and only some
of them exhibit this speed shifting... can't explain that as they claim
to all be the same version on the board and using the same SDCARD.
Literally using the same SDCARD on some has this problem and others do
not.





-- 
Brad Spencer - brad%anduin.eldar.org@localhost - KC8VKS - http://anduin.eldar.org