Troubleshot on custom board


New member
Hi all,

I built a custom board based on the Teensy 4.1
I needed more I/O than the OG teensy board could offer and I had to fit the full board in a tight space, so having a teensy mounted to a shield was not an option.
The board is working perfectly fine, I did some tests and everything is working as expected with one exception.

I added 18 pins (up to 70) in the core files and each one of them are working as expected, except the N3 pad (SD_B1_05) that has the pin 67 assigned. I followed the example in another discussion on this forum.
Whenever I'm adding the pin in the code, (Pinmode) the board is not recognize by windows until I manually enter the programing mod. I also observed that whenever the Teensy is entering the programming mode, the pin output a dimmed PWM signal (might be a serial signal?). I happen to have a LED on that pin.

I looked at the IMXRT1060m reference manual and I can't find the source of this behavior (whenever the pin is used, I loose connection to the PC).
I've looked multiple times in the core's files and everything is correctly entered. the pin is not even related to USB in any ways.

The pin is defaulted on GPIO3 so I highly doubt that it is cause by the default settings.
I suspect the USDHC2:CMD option but can't find info on it nor if it's used by the bootloader chip.

since the Bootloader code is protected and not available, I can't go any further and changing the pin will be complicated.

Any help will be highly appreciated
I did some testing.

Turns out that the DQS is daisy chained through that pin.
If I change the registry of AD_B1_09 instead, I can use the pin normally.


However, I also need AD_B1_09....

Any solution?
And the experts at NXP recommend to leave it floating... just my luck.

Yep, I'll have to print a new batch of PCB, I'll be more careful
I've added a link to this thread on the T4 bootloader page, in the footnotes under the BGA pinout diagram.

Doesn't help you now, but hopefully will help others avoid this SD_B1_05 issue on their future PCBs.