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!
Matthias
Kindest regards, Ed
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