Set HardFault exception handler?

[Erhannis]

I'm trying to figure out why my program is freezing, not even making it to the panic handler - how do we set exception handlers, like HardFault, like for dealing with stack overflows or memory access violations? (I have reason to suspect I'm running out of stack.) Following a trail of clues I wound up at

#[teensy4_bsp::rt::exception]
unsafe fn DefaultHandler(_irqn: i16) {
  cortex_m::asm::bkpt();
}

and

#[teensy4_bsp::rt::exception]
unsafe fn HardFault(_ef: &teensy4_bsp::rt::ExceptionFrame) -> ! {
  cortex_m::asm::bkpt();
  loop {}
}

or possibly

#[teensy4_bsp::rt::exception(trampoline = true)]
unsafe fn HardFault(_ef: &teensy4_bsp::rt::ExceptionFrame) -> ! {
  cortex_m::asm::bkpt();
  loop {}
}

but it doesn't seem like the first one is getting called, and the second two error with "failed to resolve: could not find cortex_m_rt in the list of imported crates". (Also with "This attribute accepts no arguments".)

[mciantyre]

Yea, it's not obvious how to register exception handlers like HardFault. In imxrt-rs/imxrt-rt#21, I documented the workaround you can use to register an exception handler. Note that the trampoline = true argument isn't going to work right now.

Most Teensy 4 users don't have a debugger connected to their MCU. If that's you, be careful when using bkpt() without a debugger. See here, or more official documentation, to understand what happens when a debugger isn't connected.

To troubleshoot your possible stack overflow, I recommend

• increasing the stack size. You can do this using environment variables. See here.
• trying using the MPU to catch the access.