Solved / Tip - Unable to boot CM4 in device mode "Failed to write correct length, returned -7"
# │forum


03/08/2023, 11:46 PM
I hit an issue where I could no longer boot any of my CM4 modules in device mode from my Mac. This was particularly annoying as I had previously booted all of them to update firmware and write the OS. Every so often one of the devices would boot past "bootcode.bin" but more often than not I would get: Failed control transfer (-7,24) Failed to write correct length, returned -7 I tried different populations of boards and boards in different slots (knowing they previously worked) - to no avail. Then I realised I had "balena etcher" still running which I was using to write the OS. I closed the app and device booting worked consistently. I now see that balena must have been probing the USB bus for new storage devices causing the boot process to work. But I though I would point this oiut in case it helps anyone.


03/08/2023, 11:49 PM
That's good to know. Thank you for the tip!


03/09/2023, 4:27 AM
Noted. This is something that is easily overlooked and could result in rage quitting.