Can breakpoints be used in in ISRs?

Question

Can breakpoints be used in interrupt service routines (ISRs)?

Answer 1

Yes - in an emulator.

Otherwise, no. It's difficult to pull off, and a bad idea in any case. ISRs are (usually) supposed to work with the hardware, and hardware can easily behave very differently when you leave a gap of half a second between each instruction.

Set up some sort of logging system instead.

ISRs also ungracefully "steal" the CPU from other processes, so many operating systems recommend keeping your ISRs extremely short and doing only what is strictly necessary (such as dealing with any urgent hardware stuff, and scheduling a task that will deal with the event properly). So in theory, ISRs should be so simple that they don't need to be debugged.

If it's hardware behaviour that's the problem, use some sort of logging instead, as I've suggested. If the hardware doesn't really mind long gaps of time between instructions, then you could just write most of the driver in user space - and you can use a debugger on that!

Answer 2

Depending on your platform, you can do this by accessing the debug port of your processor, typically using the JTAG interface. Keep in mind that you're drastically changing everything that has to do with timing with that method, so your debug session may be useless. But then again, many bugs can be caught this way. Also mind MMU based memory mappings, as JTAG debuggers often don't take them into account.

Answer 3

In Windows, with a kernel debugger attached, you can indeed place breakpoints in interrupt handlers.