Data transfer from hardware Modules to Nios

--- Quote Start ---

I've made code optimization but this didn't bring any improvement. The changes in the code above also didn't work in contrary bring more trouble cause by changing the code I stared to lose some packets (I've tested the changes separately....).

--- Quote End ---

"losing packets" could simply be a side effect of your code not waiting for the transmit to complete before issuing the next request.

After you've sped things up as fast as you can, just add a simple wait loop to delay between packet transmits and see if that affects at all your lost packets.