FPGA giving out partial answer

Hi,

without any information about your design except the two numbers, its a bit difficult to say anything.

Maybe the answer is 42 ?

But nevertheless, there is a hint here: 1536 Bytes is the maximum length of an standard ethernet frame.

If your data is somehow passing through a MAC somewere in your test setup, it will be truncated there.

But this behaviour usually can be switched off. Ethernet also defines so called Jumbo-Frames, which may be much larger.

Usage of these, i think, is not enabled per default.

Check your MAC -IPs. Presumably somewhere there is a parameter enforcing a maximum frame size of 1536.

Switch it off to allow long frames.

Might be called "enforce maximum frame size" or something like this.