SPI problems

I’m having a small problem with receiving SPI. this is the comms between two AVRs, identical settings for the SPI bus with the exception that one is set as a slave and one as a master. I send four bytes, 90% of the time it works perfectly and the timing looks like this, the “LED1″ pin I bring high when the SPI Receive interrupt is triggered and I clear it at the end of the interrupt. -

SPI Good

10% of the time it ‘misses’ receiving all four bytes, looks like somehow the SPI receive interupt isn’t always being triggered.


Anyone got any idea where to start looking? I’m perplexed.


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