I'd hoped you could divorce yourself, momentarily, from the compiler, using ONLY code that was written in ASM, and nothing but the suspect loop. First, I'd have used the ASM generated by the compiler, and then, if the problem persisted, I'd have written the code explicitly to drive this particular situation, with nothing ... meaning exactly that, aside from the code necessary to monitor the situation, and that might be nothing at all, or it might be a monitor that runs on the MCU. I'd absolutely not attempt to use an emulator or other non-MCU features, even JTAG or something else that could potentially interfere. NO HARDWARE UNINVOLVED IN THE PROBLEM SHOULD BE PRESENT ... not even in the room. Put it out in the car, or leave it at home. At least get it off the test bench. Use a logic analyzer and oscilloscope if the monitor doesn't reveal what's going afoul of the expected result.

DO NOT CONNECT A COMPUTER THAT HAS THE COMPILER TOOLKIT ON IT! Better yet, use a terminal rather than a terminal emulator on a computer.

RE