axi_dw_downsizer: AXI Slave BRESP changes in value during BVALID’s wait for BREADY

[neildaxiomise]

The AXI Slave protocol property that BRESP does not change in value while BVALID is asserted waiting for BREADY to go high is seen to be violated. The waveform shows this case.

The yellow section shows two beats of the Master AXI interface B write response channel input. The first beat is a single BVALID && BRESP handshake, then a two-cycle beat with BVALID high on both cycles and BREADY only high on the second cycle. BRESP behaves as expected, that is, not changing its value while BVALID is asserted waiting for BREADY to go high.

However, the red section shows the two beats on the Slave AXI interface B write response channel input. The first beat is a single BVALID && BRESP handshake, and the second beat shows a two-cycle beat with BVALID high on both cycles and BREADY only high on the second cycle. BRESP changes its value on the second cycle, which breaks the AXI protocol.