Re: raspberry pi zero W serial port overlay fun

[sc dying <sc.dying%gmail.com@localhost>]

On Wed, Jul 20, 2022 at 2:14 PM Patrick Welche <prlw1%talktalk.net@localhost> wrote:
>
> [I posted this to port-arm around 4th July, but hasn't made it. Reposting
>  here in case useful...]
>
>
> tl;dr On a raspberry pi zero W, updating the firmware allows the disable-bt
>       overlay to function resulting in a stable serial console.
>
> Experimental method(!)
>
> - grab https://nycdn.netbsd.org/pub/NetBSD-daily/HEAD/202207031950Z/evbarm-earmv6hf/binary/gzimg/rpi.img.gz
> - gunzip / dd to card / remove "console=fb" from first line of cmdline.txt
> - connect raspberry pi zero W 1.1 to serial port via pins 4,6,8,10 which boots
> - watch output with tip & baud rate 115200
> - all is well until /etc/rc.local is run, changing the cpu frequency,
>   which messes up the baud rate because the raspberry pi zero w, by
>   default, reserves its real UART for bluetooth, and attaches a "mini"
>   UART to the console, and this "mini" UART doesn't appear to have its
>   own clock:
> ...
> [   1.0000000] simplebus0 at armfdt0: Raspberry Pi Zero W Rev 1.1
> ...
> [   1.0000000] plcom0 at simplebus1: ARM PL011 UART
> ...
> [   1.0000000] com0 at simplebus1: BCM AUX UART, 1-byte FIFO
> [   1.0000000] com0: console
> ...
> Starting local daemons:.
> JRQ
>    ܊VP�҇KZ��     �       ���Q

Try adding this line to /boot/config.txt.

core_freq=250

[snip]
> BTW my impression is there is no bluetooth support, so we are not
> missing anything by disabling it? (as opposed to miniuart-bt).

bthfive worked at the time it was implemented till FDTized.
Currently btattach fails.

>
>
> Cheers,
>
> Patrick