Hi 6by9,
Thank you very much for your answer.
I was not aware of the fact that CM5s used the D0 revision of BCM2712. I had this in mind for RPi5 but even did not made the analogy I used a 2Gb CM5 so it could use the same chip.
Anyway, I managed to go further by swapping the file system and kernel the other way round: using the OpenWRT kernel with the Raspberry OS filesystem allowed to get the system booted successfully, so the kernel was not involved.
Then I realized the only dtb file present in the boot partition was bcm2712-rpi-5-b.dtb
Adding the others bcm2712-rpi-cm5*.dtb files made the trick and I was able to boot to prompt. I'm still facing difficulties to get an ip and log to admin webpages, but this is probably due to missing or misconfigured dhcp server and I think this is out of this forum's scope. If needed I'll try to find help on OpenWRT forum.
Anyway this brings my curiosity to this dtb mecanism I'll have to dig in to understand their role in boot sequence, what is the difference between all the cm5 dtb files to select the correct one for my board., and so on. Given the names I guess it is bcm2712-rpi-cm5-cm4io.dtb as I use an IO board designed for CM4 and don't use the lite version of the CM5.
I hope this can help others who would like to follow the same path, waiting for a CM5 specific official image file from OpenWRT guys.
Thanks again 6by9 for your valuable help, active support on this forum and sharing your knowledge.
Thank you very much for your answer.
I was not aware of the fact that CM5s used the D0 revision of BCM2712. I had this in mind for RPi5 but even did not made the analogy I used a 2Gb CM5 so it could use the same chip.
Anyway, I managed to go further by swapping the file system and kernel the other way round: using the OpenWRT kernel with the Raspberry OS filesystem allowed to get the system booted successfully, so the kernel was not involved.
Then I realized the only dtb file present in the boot partition was bcm2712-rpi-5-b.dtb
Adding the others bcm2712-rpi-cm5*.dtb files made the trick and I was able to boot to prompt. I'm still facing difficulties to get an ip and log to admin webpages, but this is probably due to missing or misconfigured dhcp server and I think this is out of this forum's scope. If needed I'll try to find help on OpenWRT forum.
Anyway this brings my curiosity to this dtb mecanism I'll have to dig in to understand their role in boot sequence, what is the difference between all the cm5 dtb files to select the correct one for my board., and so on. Given the names I guess it is bcm2712-rpi-cm5-cm4io.dtb as I use an IO board designed for CM4 and don't use the lite version of the CM5.
I hope this can help others who would like to follow the same path, waiting for a CM5 specific official image file from OpenWRT guys.
Thanks again 6by9 for your valuable help, active support on this forum and sharing your knowledge.
Statistics: Posted by Screwface2591 — Tue Mar 18, 2025 6:04 pm