[amcfarland]

For reference, is case someone runs across something similar:

We went back through things with a fine toothed comb, we were able to get the new boards to boot a few days ago.   Our bench tester power up sequence had changed (thought the board with the OSD3358-512M-BSM powered up with the same sequencing as always).   An external +3.3V to +5.0V level converter tied to UART1 and UART4 (on a USB-to-Serial convertor connected to the Test Laptop) was powering up after SYS_3V3B, where before it was first.  It is totally unclear why the UART IO pins being unknown would affect the boot up process, but we are up and running.

I would note, I found some SD images would complete U-Boot and others would not.  This could be just timing, or U-Boot may be sensitive to data in the other UARTs.

In summary: Always verify all IO are in a known state at boot time if you are having odd boot issues.

[amcfarland]

After re-walking the PocketBeagle and our board schematics for the up-teenth time, we found the SYSBOOT pullup rail had been tied to our board’s common 3.3V rail, not the OSM3358-SM SYS_VDD1_3P3V rail. We verified on the scope that the 3.3V rail powers up much later than the +5V used for VIN_AC. I checked the power rail sequence and current requirements and added a jumper tying the SYSBOOT pullups to SYS_VDD2_3P3V (we don’t have access to SYS_VDD1_3P3V). The device boots properly now.

[amcfarland]

I would be interested in a reference design covering the addition of Wifi and Bluetooth connectivity.  It appears TI makes a line of modules that mate to the AM3358.   It is possible to dig through other BeagleBoard designs, but a clear reference of the suggested minimum pinout connections and Yocto image tweaks would be great.

[Author]

Posts