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

Matthias Brugger matthias.bgg at gmail.com
Tue Nov 26 18:09:05 UTC 2019

Hi Ed,

On 25/11/2019 21:47, edrose wrote:
> Hi,
> I'm working on a project that uses the Raspberry Pi Compute Module 1. Much
> like the CM 3, the CM 1 has two UART interfaces - the main UART at ttyAMA0,
> and a second "mini-UART" at ttyS0. The project uses the main UART since it
> works better at high speeds, so the console has been bumped over to the
> mini-UART. This works fine for kernel messages and as a TTY console for
> logging in and interacting with the device, however I've been unable to get
> u-boot to present it's console over the mini-UART.
> I've worked deep enough into this to know that u-boot doesn't use the device
> tree that is set-up in config.txt, so the parameters that I've put in there
> to activate and remap the mini-UART (UART1 in dts files) to pins 40/41
> doesn't apply to u-boot. I'm using the bcm2835-rpi-b dts file currently
> since it's the best fit for the hardware, but it leaves the mini-UART port
> disabled. I've tried playing around with the dts files to enable/remap the
> mini-UART port however I've been unsuccessful.
> Can anyone give me any pointers as to how I modify the dts files to enable
> and map the second UART for u-boot to be able to use it?

Basically there are two ways.

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.

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).

Good luck!


> Kindest regards,
> Ed
> --
> Sent from: http://u-boot.10912.n7.nabble.com/
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> https://lists.denx.de/listinfo/u-boot

More information about the U-Boot mailing list