Data transfer from hardware Modules to Nios

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No its just that the code runs slower and it doesn't return fast enough to catch the next data. I've added a delay and the behavior is the same.

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Sorry, I don't understand the problem: each of those code improvements should have resulted in faster execution time for wiz_write_buf().

If they somehow made it operate slower, I guess make changes one at a time and figure out why it got slower?