Transaction Filtering Circuitry for Bus Protocol Compliance
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Solution Overview
Problem
Existing interconnect circuitry for master and slave devices faces challenges in filtering transactions without introducing significant delay or violating bus protocol requirements, particularly when handling burst transactions and arbitrary changes in input variables.
Innovation Solution
The implementation of a filtering apparatus with combinatorial filtering decision generation circuitry that maintains filtering decisions for the duration of a transfer, using storage elements to ensure consistent filtering decisions during burst transactions and address phases, and generating appropriate control signals to avoid protocol violations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If filtering operations are implemented to block certain transfers based on security criteria, then transaction security is improved, but signal routing delay increases
Solution Approach 1:
The filtering decision is generated in advance during the address phase of the transfer, before the actual data routing occurs. This preliminary filtering decision allows the routing circuitry to be pre-configured, avoiding delay during the actual data transfer phase.
Solution Approach 2:
The transfer operation is segmented into distinct phases (address phase and data phase), with filtering applied independently to each phase. This segmentation allows filtering to occur without blocking the overall transfer mechanism, maintaining high performance while ensuring security.
2Measurement precision
If filtering decisions are made dynamically based on current input variable values, then filtering accuracy is improved, but bus protocol violations occur
Solution Approach 1:
The filtering decision is made in advance during the address phase and held stable for the subsequent data phase. This preliminary decision ensures that the filtering logic remains consistent throughout the entire transfer operation, preventing protocol violations that would occur if decisions changed mid-transfer.
Solution Approach 2:
The filtering decision is applied more extensively than strictly necessary for the address phase alone, being maintained through the entire data phase as well. This excessive application of the filtering decision ensures protocol compliance by preventing any mid-transfer changes, even though the input variables might have changed.
Data Source
AI summary
An apparatus and method are provided for filtering transactions performed between a master device and a slave device, where each transaction comprises one or more transfers. The apparatus has a first interface for coupling to the master device and a second interface for coupling to the slave device. Routing circuitry is used to route, between the first interface and the second interface, signals representing each transfer. Filtering decision generation circuitry is arranged to perform a combinatorial operation to generate a filtering decision dependent on current values of one or more received input variables. The routing circuitry is then responsive to the filtering decision indicating a block condition for a current transfer, to block the current transfer by preventing one or more of the signals representing that current transfer from being passed between the first interface and the second interface in either direction. The filtering decision generation circuitry is responsive to assertion of the current transfer within the apparatus to generate the filtering decision, and thereafter to maintain that filtering decision for a duration of time that the current transfer is asserted, irrespective of a change in the values of the input variables. Such an approach provides a high performance solution while also enabling certain bus protocol violation scenarios to be avoided.