Slow Bootup on Preemptible Kernel (RT)

[ppoirier]

Hello

We are developping with ArduPilot on BeagleBone family.
There is an issue we cannot resolve with the PocketBeagle OSD3358-512M-BSM
When using Preemptible Kernel (RT) patch it takes over 90 seconds to boot.
The same kernel on a BeagleBone BLUE OSD335x C-SiP take only 15 Secs.

Here ie a link to this issue and discussion with RCNelson
https://github.com/beagleboard/linux/issues/168

Please advise

[Erik Welsh]

Unfortunately, this is probably a software issue related to the boot process. The hardware differences between the OSD335x on the BeagleBone Blue and the OSD335x-SM on the PocketBeagle are small (the OSD335x-SM integrates the EEPROM on I2C0 and reduces the size of the devices). The differences in hardware would not account for the 4x difference in boot times you are seeing.

Our speculation is that there is an issue in the boot procedure whereby the board ID value for the PocketBeagle is not enumerated properly in a some case statement. This in turn causes some kind of time out, or alternate execution path which takes much longer than the execution path for the BeagleBone Blue, which is properly enumerated. Our suggestion would be to understand the startup entire Linux boot procedure for the PocketBeagle vs the BeagleBone Blue. If you start with the BeagleBone Blue, it should be straight forward to understand when the PocketBeagle does something different on boot.

As a test, you can re-write the EEPROM on the PocketBeagle with the value from the BeagleBone Blue, but still use the PocketBeagle device tree. If you ground the “WP” test point on the back of the PocketBeagle, you can update the value of the EEPROM. See our app note (https://octavosystems.com/app_notes/osd335x-eeprom-during-boot/) for more information about how to program the EEPROM.

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