I looked over your code, I cannot see anything that appears to be a mistake. I could suggest that you consider making a couple of simple subroutines in the code, one to send a byte and one to read a byte. Your code would be much shorter and it would be easier to follow the logical flow of the program one level up from shifting out the bits.

Make sure you setup a stack properly if you start using a subroutine.

Michael Karas