Safe Mode Circuit for High Speed Serial Link Detection
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Solution Overview
Problem
High speed serial links face challenges in initial communication and training due to difficulties in linking multiple lanes, requiring careful calibration and being sensitive to clock rates, which complicates the transition from safe to high speed operation.
Innovation Solution
A safe mode of operation is introduced for high speed serial links, utilizing bit replication, frequency encoding, and programmable setup and hold times to enable communication without training, allowing for link detection and data transmission over multiple lanes with tolerance to different clock rates, and enabling a seamless transition from safe to high speed mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high speed serial link operates at high speed without training, then communication speed is improved, but reliability deteriorates due to difficulty in linking multiple lanes and sensitivity to clock rates
Solution Approach 1:
The communication process is segmented into two distinct modes: safe mode for reliable low-speed communication and high speed mode for fast communication. The transmitter and receiver each contain separate circuitry paths - a safe mode path with safe receive circuitry and a high speed path with high speed receive circuitry. This segmentation allows the system to switch between reliability-optimized and speed-optimized operation depending on the communication phase.
Solution Approach 2:
Before transitioning to high speed operation, the system performs preliminary link detection and calibration in safe mode. The safe mode transmitter transmits safe mode data at a reduced speed, allowing the receiver to detect link status and establish reliable communication before high speed data transmission begins. This preliminary action ensures the link is properly trained and synchronized before high speed operation commences.
2Reliability
If safe mode is used for link detection, then reliability is improved, but communication speed deteriorates
Solution Approach 1:
The communication system dynamically switches between safe mode and high speed mode based on the operational requirements. The transmitter includes a mode switch that selects between safe mode data transmission and high speed data transmission. This dynamic adaptation allows the system to use reduced speed for reliable link detection during initialization, then transition to high speed for normal operation, optimizing both reliability and speed at different stages.
3Productivity
If multiple lanes are used for high speed communication, then productivity is improved, but device complexity increases due to difficulty in linking and training
Solution Approach 1:
The multi-lane communication system is segmented into independent safe mode paths and high speed paths. Each path has dedicated receive circuitry optimized for its specific function. The safe mode path uses safe receive circuitry that can operate independently of the high speed path, simplifying the link detection process for multiple lanes while maintaining the ability to achieve high throughput when all lanes are properly trained and switched to high speed mode.
Data Source
AI summary
A transmitter for a high speed serial communications link, a serial communications link, and a receiver for a high speed serial communications link are disclosed herein. In one embodiment, the transmitter includes: (1) a communications interface connected to a transmission medium having multiple lanes, and (2) a safe mode circuit coupled to the communications interface and configured to send data over the transmission medium in a safe mode, wherein in the safe mode at least one of the lanes is dedicated to transmitting a link detect signal for link detection.