BBB- Disable power via USB

GoogleGroups
1

Hi,

I need to disable the BBB from booting when usb is connected to the PC. I have an external supply that powers the BBB as well as other things. I would like the configuration such that even if a user connects to the BBB via USB it will not boot until the 5V main power supply is turned on.

Looking at the schematics and SRM I know that the TPS65217C senses the USB 5V on its pin 12 and that there is some registers that control how the TPS65217C responds to different signals and these registers are written to via I2C. i just don’t know how to do that. The following thread talks about some commands that can be added to uEnv.txt to write to the TPS65217C. I just wish there was more detail on how to do this.

https://groups.google.com/forum/#!searchin/beagleboard/USB$20power/beagleboard/yNjXHmb1WnA/nlBoqnetbgcJ

Are there easy instructions to modify the registers on the TPS65217C to disable USB powerup?

hardware: BBB A5C
OS: R. Nelsons’ Ubuntu 13.04 (works great!)

Thanks

T.

2

We have no instructions on how to break the board.The TPS65217C is designed to power the board from either of these sources, whichever one come first. If 5V is connected it switches to 5VDC when connected.

One way to do what you want is to remove the power connection in your cable, cut the wire. However, if you do that, the processor will not recognize the USB as being connected and will not enumerate.

On power off, the TPS65217C clears all the registers, so any registers that are set, will be reset on power up.

Gerald

3

Gerald,

Thank you for the reply.

A hypothetical thought-experiment question… if the trace that sends USB_DC to Pin 12 of the TPS65217C is absent yet still goes to the processor (P15) would that disable the USB 5V sense of the TPS65217C yet still allow the processor to recognized the USB when powered up? Thought experiment only!!

4

Yes. Cut the trace and it should work they way you want. But, don’t expect any RMA support.

Gerald

5

Thank you for the confirmation. I just wanted to make sure my understanding of how it was working is correct.

Believe me, I understand completely regarding any modification I make are my responsibility. That’s the beauty of the BBB, you learn alot about software and hardware and a boo-boo only cost you $45. I can live with that. In my engineering career I have blown up things a lot more expensive, ha!

thanks again

6

Well why no follow? Did it work?

7

That was over two years ago and I haven’t worked with BBB since, unfortunately. However for the sake of anyone else attempting the same thing, yes it worked (on that version anyways). By cutting that trace the BBB would only boot up when the +5V was connected and not when the USB was connected.

TB

8

Thanks for the update! I'm working with the BBB right now and it's
annoying having to unplug both the USB and the 5V power to get it to
power down... so your fix might be worth doing.

9

We solved this problem by adding the following code to our uEnv.txt file:

uenvcmd=i2c mw 0x24 0x01 0x2e 0x01; if run loadzimage; then run loadfdt;run mmcboot;fi;

The i2c command writes to the power management IC TPS65271 to disable the usb power before it boots Linux. If you plugin an USB cable now, the system boost up for one second until it executes the code in the uEnv.txt file and then it goes off. That is ok for our application.