[U-Boot] Raspberry Pi Compute Module 1 mini-UART

[edrose <edrose@outramresearch.co.uk>]

Hi Matthias,

Thank you very much for your help. Unfortunately I'm still a little stuck.


Matthias Brugger wrote
> 1) as you found out U-Boot is using an embedded device tree. The device
> tree it
> uses is specified in configs/rpi_*
> I suppose you are using rpi_3_defconfig, so your device-tree is:
> bcm2837-rpi-3-b
> You can find the device-tree files in arch/arm/dts where you can change
> the files.

I had a go at this, but with little success. The Compute Module 1 is
actually based off the hardware of the original 256Mb Raspberry Pi 1. I've
tried using the bcm2837-rpi-3-b device-tree, but I just get (what I've come
to call) the Rainbow Screen of Death and nothing boots. Using the
bcm2835-rpi-b tree allows it to boot.

I tried modifying the file to include the second UART port, by adding the
following lines to the end (underneath the definition for &uart0), but
unfortunately it doesn't seem to work:

&uart1 {
    pinctrl-names = "default";
    pinctrl-0 = <&uart1_gpio40>;
    status = "okay";
};

I'm testing this by calling `coninfo` in the uboot prompt. Two serial ports
show, however only one has an address next to it and it's the address of the
main serial port. It looks like the following:

List of available devices:                                                     
serial at 7e201000 00000007 IO                                                    
serial   00000003 IO stdin                                                     
nulldev  00000003 IO                                                           
vidconsole 00000002 .O stdout stderr

Am I interpreting that correctly? Or is the serial port somehow enabled
without an address?


'Matthias Brugger" wrote
> 2) you can update the config to use CONFIG_OF_BOARD instead of
> CONFIG_OF_EMBED.
> This will take the device-tree from the file specified in config.txt (or
> to be
> correct the RPi FW will pass this device-tree to U-Boot in a register at
> startup). 

Doing this (but leaving the default device tree the same) results in no
changes to the output of `coninfo`. Is there something I need to do to tell
uboot where in memory the device-tree is stored?

I've also tried playing around with CONFIG_SPECIFY_CONSOLE_INDEX but that
had no effect either. Is there something that needs adding to the header
file to specify the serial port?

Thanks once again for your help,
Ed



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