This question: Why does my SPI-using program in C give varying results? seems to scream "I should have the
spi tag!". Unfortunately there is no spi tag.
I believe the only way to create a tag is to use it in a question, so as a hack I tried to ask a fictional one temporarily, add the tag to the question above, and then delete mine.
However, my question would not go through -- "The tag spi is not allowed!" What's up with that? Privileges here lists the required rep as 150 (which the OP of that question does not have, or I would just have suggested it in a comment).