Data transfer between fpga (14 bits) vhdl block to NIos II system (16 bits)

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Let me see if I understand your flow:

VHDL Block A --> signed 16 bit input to NIOS --> Calculation in NIOS --> signed 16 bit output from NIOS --> VHDL Block B

In this flow, the "Calculation in NIOS" is your bottleneck, especially since it seems to be floating point. Why not do:

VHDL Block A --> VHDL Calculation Block --> VHDL Block B

Say, you don't want to do this... Looking at your C code you use floating point to calculate data_new. Then you do a logic operation on it (& 0x2000). This might be the source of error. You should convert from float to hex before your do bit manipulations. Also, you may not even have to use floating point...

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Thanks Krasner for your reply, much appreciated...

VHDL Block A --> signed 16 bit input to NIOS --> Calculation in NIOS --> signed 16 bit output from NIOS --> VHDL Block B

Yes, you are right, this flow is what I intend to do

Regarding your second question, the calculation has to be done in NIios, I think I posted the same time as you, could you please see # 4, after taking your advice in# 3, I didn't use any floating point to calculate data_new.

For your information, just a trial, I also try by directly reading data from vhdl block a, then without doing any calculation, then write directly to vhdl block b, still it is not producing a sine wave to vhdl block b...if I feed directly from vhdl block a to vhdl block b, I can see a sine wave sent to vhdl block b