1. Preparing the elf file for the M4 core

Get STM32IDE, downloaded from ST's website https://www.st.com/en/development-tools/stm32cubeide.html

My machine runs Ubuntu, so it will differ. For this part it is really still just debugging the M4 core, nothing to do with remoteproc yet. You can do this part on a Windows machine, or do something similar with another Arm Cortex-M4 board

Once it is ready, create a project. Or, to have it ready for part 2, clone a code example with the following steps

bash
git clone https://github.com/STMicroelectronics/STM32CubeMP1.git

Open STM32IDE and do the following steps

  • Files
    • Open Projects from File system
      • Import Source: /STM32CubeMP1-master/Projects/STM32MP157C-DK2/Examples/GPIO/GPIO_

I use the GPIO_EXTI example.

Click build, and we get the elf file as follows

We directly use core-image-minimal, the image for the Linux side that I built in post [Yocto-STM32MP1] 1.

Note: switch the Boot mode switch to Production mode

2. Copy the elf file to the SD card

Find this file in System Explorer, then open a terminal there.

Plug in the SD card and copy that elf file to rootfs/home/rootfs.

bash
sudo cp GPIO_EXTI_CM4.elf /media/zk47/rootfs1/home/root/
sync

You need sudo to copy because that partition on the SD card needs root permission.

Okay, now connect the board, plug into the St-link port, then power up the board.

Remember to close STM32IDE before connecting ST-LINK to read the Kernel Debug Log; otherwise 2 programs both use the ST-Link and picocom conflicts with STM32IDE

3. Using remoteproc to load and run firmware on the M4 core

The board boots and we can see the elf file in home

bash
root@stm32mp1:~# ls
GPIO_EXTI_CM4.elf

We create the /lib/firmware folder and copy the elf file there

bash
mkdir /lib/firmware
cp GPIO_EXTI_CM4.elf /lib/firmware/

Now we simply configure firmware with the name of our elf file, then start it. We go to /sys/class/remoteproc

bash
root@stm32mp1:~# cd /sys/class/remoteproc/remoteproc0/
root@stm32mp1:/sys/class/remoteproc/remoteproc0# ls
coredump   device     firmware   fw_format  name       power      recovery   state      subsystem  uevent
bash
echo GPIO_EXTI_CM4.elf > firmware
echo start > state

4. Rebuilding core-image-minimal with a larger size

In the step above you will see an error that the image is too small, right? Because the yocto-built core-image-minimal is only about 14Mb; I create a bbappend that increases the size 1.5x

Create a new layer with Priority 7 (higher than meta-st-stm32mp)

bash
zk47@ltu:~/Youtube/Yocto/yocto-stm32mp1/build-stm32mp1$ bitbake-layers create-layer ../meta-stm32mp1
NOTE: Starting bitbake server...
Add your new layer with 'bitbake-layers add-layer ../meta-stm32mp1'

zk47@ltu:~/Youtube/Yocto/yocto-stm32mp1/build-stm32mp1$ bitbake-layers add-layer ../meta-stm32mp1/
NOTE: Starting bitbake server...

Edit /home/zk47/Youtube/Yocto/yocto-stm32mp1/meta-stm32mp1/conf/layer.conf, field BBFILE_PRIORITY_meta-stm32mp1 = "7"

We check show layers again

bash
zk47@ltu:~/Youtube/Yocto/yocto-stm32mp1/build-stm32mp1$ bitbake-layers show-layers
NOTE: Starting bitbake server...
layer                 path                                                                    priority
========================================================================================================
core                  /home/zk47/Youtube/Yocto/yocto-stm32mp1/poky/meta                       5
yocto                 /home/zk47/Youtube/Yocto/yocto-stm32mp1/poky/meta-poky                  5
yoctobsp              /home/zk47/Youtube/Yocto/yocto-stm32mp1/poky/meta-yocto-bsp             5
openembedded-layer    /home/zk47/Youtube/Yocto/yocto-stm32mp1/meta-openembedded/meta-oe       5
meta-python           /home/zk47/Youtube/Yocto/yocto-stm32mp1/meta-openembedded/meta-python   5
stm-st-stm32mp        /home/zk47/Youtube/Yocto/yocto-stm32mp1/meta-st-stm32mp                 6
meta-stm32mp1         /home/zk47/Youtube/Yocto/yocto-stm32mp1/meta-stm32mp1                   7

Now we create recipes-core/image/core-image-minimal.bbappend

bash
zk47@ltu:~/Youtube/Yocto/yocto-stm32mp1/meta-stm32mp1/recipes-core$ tree
.
└── images
    └── core-image-minimal.bbappend

The size shown by df -h is exactly the size of core-image-minimal.ext4 in the WORKDIR output

To change one file, the simplest way is to change IMAGE_OVERHEAD_FACTOR

bash
IMAGE_OVERHEAD_FACTOR = 5

Then we rebuild and follow the same steps as above.

The result after

bash
echo GPIO_EXTI_CM4.elf > firmware
echo start > state

Will be

bash
[   81.475582] remoteproc remoteproc0: powering up m4
[   81.689870] remoteproc remoteproc0: Booting fw image GPIO_EXTI_CM4.elf, size 2262096
[   81.697079] remoteproc remoteproc0: header-less resource table
[   81.702135] remoteproc remoteproc0: no resource table found for this firmware
[   81.709343] remoteproc remoteproc0: header-less resource table
[   81.715584] remoteproc remoteproc0: remote processor m4 is now up

Okay, now press the USER1 button on the board and LED LD5 blinks; press USER2 and LED LD6 blinks

The 2 LEDs are located here on the board