Normal Priority Write (NPW): it is also called as the best
effort traffic. There is no resource allocation and it shares the resources with the
other traffic types. It is always treated as normal priority in the PA and DDRC. There
are timeout mechanisms that can be used to prevent starvation for the PA. When there is
a timeout in the PA, that port becomes the highest priority (priority0).
Variable Priority Write (VPW): it is also called as the maximum
latency bound traffic to meet real time deadlines in video or audio applications. VPW
traffic shares the same resources with NPW in the DDRC. For the DDRC, VPW has the same
initial priority as NPW. Each command tagged as VPW has an associated latency timer.
When expired, VPW transactions have the highest priority in the controller, both in the
PA and in the DDRC. The purpose of this traffic class is to limit the maximum latency,
where this latency bound is expected to be a few hundred clock cycles.
