JTAG Master Device Inhibits Slave Resets During Debug Mode
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Debugging and programming of slave devices using external JTAG debuggers/emulators can be disrupted when master and slave devices are of different technologies or manufacturers, as the master device may inadvertently reset the slave devices, failing to distinguish entry into programming/debugging mode and thus interfering with the debugging operation.
Innovation Solution
The implementation of a watchdog reset inhibit function using the TRST* signal from the IEEE 1149.1 JTAG standard, which detects when slave devices enter programming/debugging mode and inhibits resetting, ensuring continuous operation by preventing the master device from sending reset signals during this mode, and utilizing an external watchdog/reset circuit to control multiple devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the master device continuously sends reset signals to slave devices, then the slave devices maintain deterministic initial states, but the programming/debugging operation is disrupted when slave devices enter programming mode
Solution Approach 1:
The master device detects the TRST* signal from the slave device to determine whether the slave is in programming/debugging mode. Based on this feedback, the master device dynamically adjusts its reset behavior: inhibiting reset signals when the slave is in programming mode and allowing reset signals when the slave is in normal operation mode. This feedback mechanism resolves the contradiction by adapting the reset behavior to the current operational state.
Solution Approach 2:
The reset inhibition mechanism transitions from a static continuous reset approach to a dynamic conditional reset approach. The master device changes its reset signal generation based on the detected operational mode of the slave device, making the system adaptable to different states. This dynamic adjustment allows the system to maintain deterministic initial states during normal operation while enabling uninterrupted programming/debugging operations.
2Productivity
If the master device inhibits resetting slave devices during programming mode, then uninterrupted programming/debugging is enabled, but the master device must detect and respond to programming signals from different technologies
Solution Approach 1:
The master device implements a universal detection mechanism that recognizes the TRST* signal across different JTAG implementations and technologies. By using the standard TRST* signal as a universal indicator of programming mode, the master device can inhibit resetting for slave devices from various technologies and manufacturers without requiring technology-specific detection logic, thus managing complexity while achieving multi-functionality.
Solution Approach 2:
The TRST* signal acts as an intermediary mechanism that carries information about the slave device's operational state to the master device. This intermediary signal allows the master device to indirectly determine whether the slave is in programming mode without directly analyzing the slave's internal state or requiring complex communication protocols, thereby simplifying the detection and response mechanism.
3Adaptability or versatility
If the master device uses TRST* signal detection to inhibit resetting, then compatibility with different technologies is improved, but the system requires external watchdog/reset circuits to control multiple devices
Solution Approach 1:
The TRST* signal serves as a universal indicator that works across different JTAG technologies and manufacturers. By relying on this standardized signal, the master device achieves broad compatibility without requiring technology-specific detection mechanisms. The external watchdog/reset circuit leverages this universal signal to control multiple devices of different technologies, eliminating the need for separate detection and control mechanisms for each device type.
Solution Approach 2:
The external watchdog/reset circuit creates a simplified copy of the reset control function that operates independently of the complex master-slave device interactions. Instead of directly managing the complexity of multiple devices with different technologies, the watchdog circuit uses the TRST* signal as a trigger to inhibit resetting, providing a streamlined control mechanism that works across all supported devices.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Embodiments of the invention include methods, systems and devices for implementing the auto detection of Joint Test Action Group (JTAG) debuggers/emulators. Embodiments include sending a reset signal to reset one or more slave devices (206), and detecting a programming signal indicating the one or more slave devices (206) are in a programming/debugging mode. Embodiments also include responsive to the signal, inhibiting resetting one or more slave devices receiving the programming signal.