BeagleBoneBlack not booting with custom cape on

Hello,

I am using the BeagleBoneBlack (BBB) in the educational sector. For a project I designed a cape. It all works very nice, if I plug in the cape one the BBB is started. My OS is on the eMMC and I use the SD-Card rarely for storing files.

If I boot the BBB with the cape, it won’t work. I suspect it has something to do with my using reserved pins for the HDMI, although I do disable them in the uEnv.txt.
Booting with only the Cape connected to P9 works fine.

On P8 is use the Pins: 11,14,15,16,17,19,31,32,33,34,35,7,38,45.
In Derek Molloys Chart they are marked as reserved for hdmi.

For a dump of uboot see below.

Do you have an idea how what the problem is and how I can solve it?

Thank you very much in advance!

Kind regards,

Jan

— uboot dump —

If it were the reserved pins that were at fault, you would not be getting a printout from the serial port as the board would never boot anything.

Gerald

Be careful that your cape does not put a resistive load on those pins. I had an LED switching network connected to Pin 8.44.
This causes the BBB to not boot.

I don’t have my documentation with me, but there are several pins which have this property.

I added a series resistor, I think about 50kohm, which allows the LED switch circuit to work, but decreased the load enough for the boot process to proceed successfully.

I was using a BJT switching circuit. A MOSFET switch with very high input resistance would not have caused this type of problem.

Regards,
Greg

Look at page 67 and 68 of the “Beaglebone Black System Reference Manual” regarding the “Boot Configuration”.

Also this discussion:

https://groups.google.com/forum/#!category-topic/beagleboard/DdPYCIUB-Sg

Regards,
Greg