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MC9S08QE128 KBI interrupt issues - sometimes second interrupt does not fire after the first one

Question asked by Petras Cerniauskas on Feb 8, 2016
Latest reply on Feb 12, 2016 by Petras Cerniauskas

Hello! We have a product based on Freescale MC9S08QE128 MCU that uses 2 KBI interrupt pins to determine time difference between certain related external events that are a few (2-20) milliseconds apart. As KBI interrupt fires our KBI ISR loops while KBF == 1 disabling any asserted KBI pins and setting KBACK = 1 effectively making sure that when we leave KBI ISR we are ready to receive new KBI interrupt. The problem is that sometimes after the first interrupt fires the second interrupt does not. I studied KBI block diagram and I understand that any enabled asserted KBI pin will prevent generation of new KBI interrupt. But it seems to me there is a potential MCU bug where even if asserted pin is disabled it prevents generation of new interrupt. This same behavior was mentioend by Javier Rodriguez in "MC13213 : Problem using KBI interrupt" thread. Assuming this is MCU bug is there a workaround besides polling of second KBI line after the first interrupt? Thanks!