Low Priority Read (LPR): also called “the best effort traffic”.
There is no resource allocation and it shares the resources with the other traffic
types. LPR is always treated as low priority in the PA and in the DDRC. There are
timeout mechanisms that can be used to prevent starvation for both the PA and the DDRC.
When there is a timeout in the PA, that port becomes the highest priority (priority0).
When there is a timeout in the LPR store in the DDRC (in other words, LPR store becomes
critical), the LPR entries are served before HPR entries.
Variable Priority Read (VPR): also called “the maximum latency
bound traffic” for meeting real time deadlines in video or audio applications. VPR
traffic shares the same resources with LPR in the DDRC. But, based on the configuration,
it may have a dedicated queue (red or blue) in the XPI. It has the same priority as LPR,
but lower priority than HPR for the PA. For the DDRC, VPR has the same initial priority
as LPR. Each command tagged as VPR has an associated latency timer. When expired, VPR
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.
High Priority Read (HPR): it has allocated resources. If the
XPIs are configured to have dual read address queues, then the red queue can be
allocated to HPR. For DDRC, HPR traffic goes to its own dedicated store. HPR traffic has
higher priority than LPR. HPR is meant for latency critical but not real time
applications such as CPU.
The online versions of the documents are provided as a courtesy. Verify all content and data in the device’s PDF documentation found on the device product page.
