In non-live presentation mode, A/V data is fetched from memory through the AXI master port using the local DMA controller (DPDMA). Because the data is not timed, A/V timing is locally generated in the DisplayPort controller using the internal A/V timing generator. The DPDMA is driven to fetch data so as to ensure continuous A/V data flow with no underflow due to memory latency fluctuations (a suitably sized FIFO is included). Two non-live inputs are supported: video and graphics, which can be mixed together using alpha blending or chroma keying.
To assist in A/V synchronization, the A/V presentation time must be captured as a timestamp relative to a system time clock, and associated with A/V presentation units (e.g. video frames and audio buffers), and provided to software, for example, by storing the timestamp in the DPDMA descriptor.