Hi all,
Let me start off by saying that I love the teensy and thank you to everyone on these forums and of course Paul!

So unfortunately I've discovered that when using teensyloader 1.52 and 1.53 (arduino 1.8.12 and 1.8.13), chibios does not work properly on the Teensy 4.
Here is a link to the chibios library: https://github.com/greiman/ChRt
What happens is that the program compiles properly and uploads but then renders the teensy dead - not even running the setup code. When trying to reprogram it, it does not get automatically programmed and I have to manually press the program button on the teensy to get it to respond.

I did some experimentation and found that teensyloader 1.51 on arduino 1.8.12 works fine, so it must be 1.52 that breaks it.

I also tried it with a second Teensy 4 with a different cable and same issue.

Thanks in advance for your help!