AnsweredAssumed Answered

STM32L476 USB inconsistencies.

Question asked by shingadaddy on Mar 29, 2017
Latest reply on Dec 19, 2017 by waclawek.jan

I've been working with USB on my Nucleo board(S)  for some time now. Been comfortably successful at getting a few operational interfaces working with it. Including DFU. STM32L476. So time to make our own PCBS! We knocked out an order for 10 . Production needing 7 and having a few SPARES to help wear off the new. Ran into a little problem and I turned in an online help request. Waited all day and thought maybe someone there might notice I marked it Critical. Not sure of the turnaround time but everybody's critical  might be a little different. Hope I hear and in the mean time here's where I got too.

We have 10 Brand new (Identical) PCB's with STM32L476VG's on them.

They use the direct connected USB for communication. (PA11/PA12)

They are *all* loaded with the same binary, VIA DFU.

DFU works. Dependably.

The binary is the STM32CubleL4 HAL DEMO from EVAL board, with IO EXPANDER commented out. This runs the LEDS on EVAL and is the only thing needed to be removed for this to work. I figure it works good as a TEST LOAD.


Operationally :

  7 Enumerate/seem to work.  ------  3 DO NOT even enumerate correctly.


Do not meaning: 2 -  with DEVICE NOT RECOGNIZED responses.  1 -  PC IGNORING COMPLETELY


I use VBUS DETECT. USB 5VDC is getting to PA9 on the one the is completely ignored.  

We have matched lines on the USB traces about .7 inches between the type C USB connector and the MICRO. Connectivity is direct via usb line suppressors (TI_SN65220DBVR). No inline resistors. No Pull up on D+.I am going to gather these up personally and look into it. But this is being tested by very capable individuals with years of experience and there does not seem to be a difference in the PCBS PHYSICALLY or SIGNAL WISE. The code that is running on them is the STM32CubeL4 USB in DEVICE MODE -CDC DEMO from the EVAL project in TrueStudio.

My immediate questions would be.

1. Suggestions such as the "Oh yeah" type, as to what might be wrong?.

2. Since DFU mode works, (and 7 others) shouldn't the enumeration at least be functional on the operational testing?

3. Does DFU USE a different SPEED that is not as critical as USB FS.

4. Does the MSI trimmed with LSE, really provide precision/stability good enough for USB FS?

Crystal = Abracon ABS25-32.768KHZ-T

This is our first 10 in a production run and we are now a little nervous on the 70% operational aspect.

Power = CLEAN



Ground plane internally.

I had one nucleo dev board (Out of 5 or 6) that I used for a while until it acted like it had a heat sensitivity problem after some operational time. Then DEVICE NOT RECOGNIZED. On more than one computer. Unless I left it unplugged for about 30 minutes. Then BACK IN BUSINESS !   THAT is flakiness at its finest. And now I think - maybe we have more?


Just thought I'd drop this here too and see if anyone had any ideas. I really didn't think I had to get the LED out and chase it though the code (again) But here I am. Not amused at all.


Any input appreciated.

Thanks folks.