Data transfer from hardware Modules to Nios

Couple of things:

send() and wiz_write_buf() appear to work off of lengths in units of 16-bit words, not bytes.

Your test_tcps() is saying send 32 of them but I think you only need 16?

Then, your wiz_write_buf() taking 35us means >1us per each of your (32) writes that you are doing.

I would quickly try some things like at least turning on the compiler optimization and maybe inlining the wiz_write_buf() loop and function calls, to try to reduce the loop overhead. Even with a conservative budget of 250ns per write taken by the tri-state timing, you're losing 3x that (another 750ns) on loop overhead. NIOS isn't a great performer, but I think you should be able to manage better than that.