JTAG Device Synchronization via State Diagram Sequences
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Solution Overview
Problem
JTAG-enabled systems, particularly in star configurations, do not allow for hot disconnecting and reconnecting of devices during scan chain operations, and devices powering up in an operational system cannot participate in communications or testing due to unawareness of the system state.
Innovation Solution
A method where a newly powered device waits for a synchronization point sequence on a shared bus to synchronize with the system state, allowing it to implement a predetermined feature set and participate in system operations, using a synchronization point sequence embedded in a change packet to ensure all devices follow the same state diagram.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a device is power cycled in an operational JTAG system, then the device can conserve power or be reset, but the device cannot participate in system communications or testing because it is unaware of the current system state
Solution Approach 1:
The system performs preliminary actions by inserting synchronization packets into the scan chain before the powered-off device is reconnected. These packets contain state information that prepares the system for the device's return, enabling seamless integration without disrupting ongoing operations.
Solution Approach 2:
Synchronization packets act as intermediaries between the operational system and the newly powered device. These packets carry state information and instructions that bridge the knowledge gap, allowing the device to understand and join the current system state without direct communication during its powered-off period.
2Stability of the object's composition
If all devices follow a common state diagram in concert, then system-wide coordination is achieved, but newly powered devices cannot interpret signals correctly because they are unaware of the current state
Solution Approach 1:
The system provides feedback to newly powered devices through synchronization packets that contain information about the current system state. This feedback mechanism allows devices to understand their position in the state diagram and correctly interpret subsequent signals without disrupting the coherent state transitions of the entire system.
Solution Approach 2:
Synchronization packets are inserted in advance into the scan chain to provide newly powered devices with the necessary state context before they need to interpret signals. This preliminary action ensures devices can immediately participate in state diagram transitions without confusion.
3Reliability
If JTAG systems operate according to a system-wide state diagram, then coordinated testing and communication are enabled, but hot disconnecting and reconnecting of devices is not permitted
Solution Approach 1:
The system dynamically adapts to device hot plugging events by detecting when devices are disconnected or reconnected and inserting appropriate synchronization packets at those moments. This dynamic response allows the rigid state diagram protocol to accommodate flexible device connectivity changes without compromising coordinated testing capability.
Solution Approach 2:
The system performs preliminary actions by pre-inserting synchronization packets into the scan chain anticipating device reconnection. This allows devices to be hot-plugged without disrupting the ongoing state diagram operations, as the synchronization information is already in place to guide the device back into coordination.
Data Source
AI summary
A method comprises a system comprising a host device coupled to a first remote device actively operating according to a state diagram that the host device and all remote devices follow during operation of the system. The method further comprises powering up a second remote device while the host device and first remote device are actively operating according to the state diagram. The second remote device waits for a synchronization point sequence. Upon detecting the synchronization point sequence, the second remote device implements a predetermined feature set and synchronizes itself to the state diagram at a common point as the host device and first remote device.