Custom Teensy 3.2 Board programs but disappears

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Hello everybody!

I've been developing a control system based on the Teensy 3.2 module and I finally rolled out my own boards based on the Teensy 3.2 reference design!
I bought a few MKL04 chips from Paul a while back and put two boards together - one with only the Teensy core components and VREG and one with that and all the additional periphery I designed around it.

Both boards show the same behavior.
If I plug in an USB cable, no device shows up in Device manager.
If I prepare a sketch for uploading and press the Program button, the PC registers an USB device, completes upload and loses the USB device again. That happens very fast.
The code in the sketch does not seem to execute.

Voltage regulation seems nominal and RESET & PROG are normally high.

I posted my schematic and PCB layout if you would like to look.
SCHEMATIC.PNGPCB.PNG

It's worth noting that I tried starting the board with and without the parallel caps to X2, it did not yield different results.
I did use a rather heavy Abracon ABMM2 18pF crystal, so that mighty be what's upsetting it.

I don't know where to start looking for signs of life. Any tips where to start?

Thanks!
Best,
S
 
I don't know where to start looking for signs of life. Any tips where to start?

First check the Teensy Loader's Help > Verbose Info. Sounds like things are working, but just double check to make sure it says all the blocks for your code were programmed.

If that looks good, maybe try editing mk20dx128.c to turn on a LED very early in the boot process. Remember, you need to turn on the GPIO clock, then write to the pin config register, then write to the direction register, and then write to the output register. Test your code on a regular Teensy 3.2.

If you can get the LED to light up with the 4 register writes at the very beginning (even before the watchdog disable), then start moving them farther into the boot process until you figure out where it's getting stuck.

Good luck! ;)
 
Thank you all for the feedback - I figured it out! A faulty footprint of the BAT54C caused the VBAT to remain low and that tripped the whole setup.

During my research I stumbled over a post that was describing the same "symptoms", but in their case it was caused by flipped D+ & D- signals on the USB so I tried this as well, but that just caused widows to report a device malfunction

Thanks for the tip Paul, it was useful to take a look at the mk20dx128.c, I now have a better understanding of how the init process runs!

Moral of the story - you can never be too vigilant with the footprints, I must have checked them at least 4 times..

I'm (almost) sorry it wasn't a weirder problem!

Thanks for jumping in!
 
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