STM32MP135 Dev Board Buildroot

A Buildroot external tree for a custom PCB based on an MYiR MYC-YF135-256N SoM.

TODO: Add PCB Design Files

Harwdare

STM32MP135DAF7 inside the MYC-YF135-256N SoM from MYiR Electonics.
- 1 GHz
- 256MB RAM
- 256MB NAND (not used in this example)
Silicon Labs WF200D WiFi chipset.
Ti PCM3060 audio codec.
40-pin LCD, and 6-pin CTP connector compatible with Orient Display 480x272 TFT LCD panel.

Current State

Uses Linux kernel v6.1 (from STM)
Uses U-Boot 2023.07 (from STM)
Uses TF-A v2.8 (from STM)
Uses Optee-Os v3.19.0 (from STM)
Tested with Buildroot 2023.05
Uses mainline STM32 dtsi where possible, however some of the dt-bindings for the STM32MP135 have not made it to the mainline u-boot and Linux source yet. Fortunately STM provides customised TF-A, Optee, U-Boot, and Linux.
Includes a file system overlay with some configuration, but boot/extlinux.conf is the only file which is actually required.
Some other files in the overlay folder are just to override defaults or test features but are not strictly required.

Usage

Use like any external buildroot tree:

Clone this repository, as well as Buildroot.
In the Buildroot directory, create a config file based on this external tree:

BR2_EXTERNAL=../STM32MP135_Dev_Board_Buildroot make stm32mp135_dev_board_defconfig

Review or modify the system in make menuconfig.
Build the image using make.
NOTE: There is an issue with UBoot the first time you try to build, see below.
Use dd, Rufus, or your software of choice to image an SD card with the output/images/sdcard.img file.

Issues

A patch is included to modify the conf.mk file in output/build/optee-os-custom/core/arch/arm/plat-stm32mp1 to support 256MB RAM. Further information on the process is described by STM here. If you're getting errors about things being in the wrong memory location it could be a related issue.

WARNING: The load address in optee header 0xce000000 - 0xce081310 is not in reserved area: 0xce200000 - 0xd0000000.
ERROR:   OPTEE header parse error.

There is a problem with the PCM3060 driver reporting which format the codec supports. Although it seems to be correct, it doesn't seem to work and was giving an error:

44004000.audio-controller-pcm3060-dac: ASoC: pcm3060-dac <-> 44004000.audio-controller No matching formats

A patch is included to modify linux-custom/sound/soc/codecs/pcm3060.c on line 189, and change the .format to SNDRV_PCM_FMTBIT_S32_LE. TODO: Create a patch file for this.

The Overlay Folder

There are a few config files in the overlay file for either quality of life, or to make things actually work. Most are optional depending, or may even conflict with your desired settings.

/boot/extlinux.conf - Required to boot linux. U-Boot will look for this.
/etc/init.d/S40xorg - A dummy file to overwrite a default which is creatred when Xorg compiles.
/etc/opkg/distfeeds.conf - Contains OpenWRT package feed. Need to force it to search the correct architecture when using opkg.
/etc/X11/xorg.conf - Sometimes the default are bad, sometimes they aren't.
/etc/directfbrc - DirectFB config file because it doesn't seem to use FBDev by default, even though it says it does.
/lib/firmwmare/wfx - Firmware files for some wifi cards. SiliconLabs GitHub.
/root - Just some extra files for testing and playing with.

Trips and Tricks

Some things that caught me out, or helped me out, along the way:

I had trouble figuring out how to convince ARM Trusted Firmwawre to build a FIP package from within Buildroot. For reference, or if you want, or need, to create one manually you can do so from within the buildroot/output/build/arm-trusted-firmware/build/stm32mp1/debug directory:

fiptool create --tos-fw bl32.bin --fw-config fdts/stm32mp135_dev_board-tf-a-fw-config.dtb --hw-config u-boot.dtb --nt-fw u-boot.bin --tos-fw-config fdts/stm32mp135_dev_board-tf-a-bl32.dtb fip.bin

Where the u-boot.bin, and u-boot.dtb files are found in the buildroot/output/build/uboot directory.

Remember that the FIP package contains the second stage bootloader, and loads the U-Boot DTB file. So if you modify the device tree you will need to manually rebuild U-Boot, and ARM Trusted Firmware, and probably the Linux kernel as well depending on your changes.

make optee-os-rebuild
make linux-rebuild
make uboot-rebuild
make arm-trusted-firmware-rebuild
Finally; make to generate the image.

I had to install libssl-dev for the OpenSSL Headers in order to build ATF.
The WiFi was getting buffer errors when the SPI bus was running at 42MHz. It seems to be fine at 24MHz, it might be able to run a bit quicker but I haven't tried yet.
The /etc/X11/xinit/xinitrc file, by default, opens several xterm windows and starts a window manager. You may want to check and modify the last few lines of this file to suit your needs.

BasicCode / STM32MP135_Dev_Board_Buildroot