Raster Operations Unit Interleaving Read Write Requests
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Solution Overview
Problem
In unified memory architectures, the raster operations unit (ROP) faces performance bottlenecks due to inefficient use of conventional bus protocols like PCI Express, which are not optimized for bidirectional data transfer, leading to significant overhead in read-modify-write sequences for the frame buffer.
Innovation Solution
The ROP unit interleaves read and write requests to efficiently communicate with the frame buffer via a PCI Express link by using separate upstream and downstream data paths, processing pixels in groups and generating read requests for one group while writing back modified data for another group, thereby balancing data transfer activity on both paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the ROP unit uses conventional bus protocols like PCI Express for data transfer, then system cost is reduced, but bus turnaround overhead increases significantly
Solution Approach 1:
The patent segments the data transfer operations into separate read requests and write requests, allowing them to be transmitted on different data paths (upstream and downstream) simultaneously. This segmentation enables parallel processing of read and write operations, eliminating the sequential turnaround overhead inherent in conventional reversible bus protocols.
Solution Approach 2:
The patent introduces a new dimension to data transfer by utilizing separate upstream and downstream data paths that operate independently. Instead of switching between read and write modes on a single path, the system transitions to a two-path architecture where read and write operations occur concurrently in different dimensions of the data transfer space.
2Reliability
If the ROP unit processes pixels in groups with sequential read-then-write operations, then data coherence is maintained, but data transfer efficiency decreases
Solution Approach 1:
The patent implements preliminary action by maintaining separate read and write request queues that are prepared and managed independently. Read requests for subsequent pixel groups are queued and ready to be transmitted as soon as the current write operations complete, eliminating idle waiting time while ensuring data coherence through proper sequencing of the interleaved operations.
Solution Approach 2:
The patent achieves continuity of useful action by keeping both upstream and downstream data paths continuously active through interleaved read and write operations. Instead of having periods where one path is idle while the other is busy, both paths maintain continuous useful action, maximizing data transfer efficiency while preserving data coherence through the interleaved sequencing.
Data Source
AI summary
A raster operations (ROP) unit interleaves read and write requests for efficiently communicating with a frame buffer via a PCI Express (PCI E) link or other system bus that provides separate upstream and downstream data transfer paths. One example of a ROP unit processes pixels in groups, performing read modify writeback sequences for each group. The read requests associated with pixels in a second group are advantageously interleaved with the writeback requests for pixels in the first group prior to sending the requests on the system bus.