Hub Interface Unit Command Reordering for EDMA Priority
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Solution Overview
Problem
Current microprocessor designs with Enhanced Direct Memory Access (EDMA) systems face issues where lower priority data transfers block higher priority transfers, especially when interfacing with slow peripherals, due to the sequential handling of commands without consideration of priority.
Innovation Solution
The implementation of a hub interface unit (HIU) that reorders commands based on priority, ensuring that higher priority transfers are issued first by manipulating pointers in the command queue and read response queue, allowing for proper handling of data transfers regardless of the order received from the transfer controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If commands are handled sequentially in the order received from the transfer controller, then the system maintains simple command processing logic, but lower priority transfers block higher priority transfers causing loss of time
Solution Approach 1:
The hub interface unit performs preliminary reordering of commands in its internal queue before issuing them to the peripheral. Commands are received from the transfer controller, stored in the HIU command queue, reordered by priority level, and then issued in the correct priority sequence. This preliminary action ensures high priority transfers are not blocked without adding complexity to the transfer controller itself.
2Loss of time
If the EDMA interfaces with slow peripherals using sequential command handling, then the interface remains simple, but high priority transfer requests are delayed causing loss of time
Solution Approach 1:
The hub interface unit acts as an intermediary between the transfer controller and the peripheral. It receives commands from the transfer controller, buffers them in its internal queue, reorders them by priority, and issues them to the peripheral. This intermediary structure isolates the complexity of priority reordering from both the transfer controller and the peripheral, allowing high priority transfers to be expedited without complicating the overall system architecture.
3Productivity
If commands are issued to peripherals in the order received, then the system maintains ease of operation, but productivity is reduced when high priority transfers are blocked
Solution Approach 1:
The command processing function is segmented into two independent parts: the transfer controller that issues commands and the hub interface unit that reorders and manages command issuance to the peripheral. This segmentation allows the HIU to implement complex priority-based reordering without affecting the simplicity of the transfer controller's operation. The peripheral continues to receive commands in a simplified manner while the HIU handles the complexity of priority management internally.
Data Source
AI summary
Command reordering in the hub interface unit (HIU) of Enhanced Direct Memory Access (EDMA) functions is described. Without command reordering in the EDMA, commands are issued by the HIU to the peripheral in order of issue. If the higher priority transfers are issued later by the EDMA, the previously issued lower priority transfers would block the higher priority transfers. Command reordering in the HIU causes transfers to be reordered and issued to the peripheral based on their priority. Reordering allows the EDMA and HIU to give due service to high priority transfer requests with decreased weight placed on the order in which the requests were issued.