NCO and FIR COmpiler Megafunction performance

Thanks for example, I have to correct my previous statement. In the discussed assignment, the expression bit length is context determined. So kaz was right about correct evaluation to 19 bit.

mix <= fsin_o +fsin_o_2 + 0;

The waveforms seems to indicate an overflow, but it's actually the result of a wrong number display format, signed instead of unsigned. The same thing happens in your example.

You have to care however, that NCO output and FIR filter are using the same number representation. If they are different, the filter will get a distorted input signal. I guess this happens in your test. You can change from unsigned (offset binary) to signed representation by inverting the MSB.

I apologize for causing confusion.