Source Code and Examples for Embedded Systems Lab 2023 for M. Tech EE Students
Also availablt on Github: https://github.com/PEG-IITDH/EmbeddedLab2023
Abhijit Kshirsagar Kshirsagar
85a2491634
Problem: It is seen that the GPIO ISR was getting called more than once for every button press. Diagnosis: The last instruction in the GPIO Interrupt handler is a write to the ICR register which clears the interrupt. However, this write takes multiple cycles, depending on the caching involved. As a result, after the instruction to write to ICR, the microcontroller exits from the ISR function but the write has not yet completed. The controller sees this as a pending interrupt and goes into the ISR again. However, by the time the controller enters the ISR this second time the ICR write has indeed happened, and it appears to be a spurious interrupt call. If the code is run in single-step debug mode, it gives the code enough time to write to the ICR register and therefore the ISR is not called a second time. Solution: Wait for a few cycles *after* the ICR write instruction and before exiting from the ISR. The official documentation recommends a DSB instruction but that may not be enough to account for vendor-specific write-caching. In such a case a simple write to a register location should be enough. Additional Info: https://developer.arm.com/documentation/ka003795/latest/ |
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