Pin 8_44 boot interference

Hi All…

I use pin 8_44 for digital input to the PRU. For those new to this issue, that is one of several pins that can change the boot behavior of the BBB, but the bottom line is that it should not be connected on startup. I didn’t know that when I started my project, but it wouldn’t have made a difference in my selection since input/output to the PRUs is fundamental to what I need to do and I would use any PRU pin I can get access to.

Currently, I have to disconnect the BBB every time I reboot the Beaglebone. This was not a problem at first, but now I use the device remotely quite a lot, and sometimes I have to reboot the entire PC that is local to the Beaglebone. I’ve tried rearranging the circuitry, but because I use a protection diode to allow >3.3V as a digital input, I have been unable to find a balance between high enough impedance to prevent boot issues and low enough to consistently recognize the digital inputs I need to measure.

Is there a simple way to disable the feature that looks for boot options on this pin (and any others)?

Thanks so much,



The boot pin sensing is fundamental to how the processor works.
It can not boot without that function.

The proper question to ask is how do I prevent my I-O from disturbing the boot process.
The solution is probably something like adding transmission gates that does not connect your I-O until System_Reset goes high.

— Graham

The CPU requires that function to boot.

The question you should be asking is how do you design your circuit, so that it does not interfere with the boot process.

Probably would require something like a transmission gate that does not connect your circuit to the pin until the System_Reset line goes high.

— Graham