lpcware

LPC4333: can't boot from USB

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by svenb on Sun Oct 19 11:24:33 MST 2014
Hi!

I have a LPC4333 which is on a self-made board. I'm trying to use the USB bootloader feature but can't get it to work, and I'm quite clueless about what is wrong. Maybe someone here has a hint on how to continue debugging this issue.

I configured the boot pins to boot from USB, then I toggle the reset pin. In dmesg, I then see this message:
[28578.835904] usb 2-1.1: new full-speed USB device number 33 using ehci-pci
[28578.902738] usb 2-1.1: device descriptor read/64, error -32

That is reproducable every time.
Since it looks like a communication problem, I attached my scope to the USB traces, and what I see there is this:
https://imgur.com/a/sI8GD#0

The communication looks perfectly clean for a while, then suddenly after the second reset, D- goes low in a weird pattern.

I checked the power supply; there are no spikes visible when the fault happens. There's also no excessive noise visible on the supply lines. I tried with a different USB cable as well. Here's a log from Linux' usbmon USB debugging tool for the communication which happens: http://paste.kde.org/piusouoga/didzqr/raw
I am not familiar enough with the USB protocol yet to read much from that to be honest; it seems like everything goes well for a while, then the error -32 fault happens but after that communication continues for a while. What also confuses me is that the fault is visible after ~70ms on the scope, but this log shows communication much later.

Another surprising thing is that the fault happens pretty much exactly 20ms after the start of the second reset. Does something special happen 20ms after a reset finished?

Might the USB PHY have been damaged during soldering? Could that fit the error I see?

As said, I am really quite clueless on this issue (I will continue trying to understand how USB initiation works though), so any hints and ideas would be appreciated.

Thanks and best regards,
Sven

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