I3C In-Band Interrupt Backoff Timing for Fair Bus Access
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Solution Overview
Problem
Lower priority I3C slave devices are starved of service due to priority-based servicing on a serial bus, leading to ineffective bus access and lack of acknowledgment for their interrupt requests.
Innovation Solution
Implementing a backoff timer in slave devices to store a backoff time, inhibiting them from initiating in-band interrupt requests until the timer expires, ensuring fair access to the bus by refraining from competing during high contention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If priority-based servicing is implemented on the serial bus, then higher priority slave devices are serviced first, but lower priority slave devices are starved of service
Solution Approach 1:
The backoff timer implements periodic action by requiring higher priority slave devices to wait for a predetermined time period before re-asserting interrupt requests. This periodic interruption of the interrupt assertion pattern allows lower priority devices to access the bus during the backoff period, ensuring fair service distribution while maintaining priority-based servicing speed for critical devices.
2Ease of operation
If lower priority slave devices continuously assert interrupt requests, then they seek bus access, but bus congestion occurs and service is denied
Solution Approach 1:
The backoff timer mechanism performs preliminary action by proactively establishing a waiting period for higher priority devices before they can re-assert interrupt requests. This advance timing control prevents bus congestion by ensuring that not all devices assert interrupts simultaneously, thereby simplifying bus contention management while maintaining ease of operation for lower priority devices.
3Reliability
If backoff timer is implemented in slave devices, then lower priority devices get bus access opportunities, but interrupt service latency increases for higher priority devices
Solution Approach 1:
The backoff timer mechanism applies parameter changes by dynamically adjusting the timing parameters of interrupt assertions. Higher priority devices must wait for the predetermined backoff time period, which temporarily increases their service latency, but this time parameter adjustment ensures fair service distribution to lower priority devices, thereby improving overall service fairness.
Data Source
AI summary
A process for a slave device on a serial data bus to make an in-band interrupt request to a master device includes checking whether a backoff time stored by a backoff timer has expired. When the backoff time has not expired, the slave device refrains from initiating the in-band interrupt request to the master device in response to a start condition on the serial bus. However, when the backoff time has expired, the slave device is permitted to initiate the in-band interrupt request to the master device in response to the start condition on the serial bus.