JTAG Interface Signal Reuse for Multi-Port Access
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Solution Overview
Problem
Existing electrical devices with JTAG Test Access Ports lack a method to selectively reuse their external interface signals for accessing various types of access ports, limiting flexibility in testing and debugging operations.
Innovation Solution
A method and apparatus that allow the JTAG interface signals (TDI, TMS, TCK, and TDO) to be used for selectively accessing JTAG Test Access Ports, JTAG compliant Access Ports, JTAG compatible Access Ports, and non-JTAG Access Ports, utilizing an Access Port Selector circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the JTAG Test Access Port interface signals are dedicated solely to JTAG testing, then reliability and standard compliance are improved, but adaptability and versatility for accessing different types of access ports deteriorate
Solution Approach 1:
The patent implements a dynamic access port selection mechanism where the same physical JTAG interface signals can be dynamically configured to access different types of access ports (JTAG Test Access Ports, JTAG compliant Access Ports, JTAG compatible Access Ports, or non-JTAG Access Ports) based on selection signals. This allows the interface to change its functional state without physical reconfiguration, resolving the contradiction between dedicated JTAG functionality and multi-purpose adaptability.
Solution Approach 2:
The patent creates a universal access interface where a single JTAG interface signal set serves multiple functions by enabling access to four different types of access ports through the Access Port Selector. This multi-functionality allows one physical interface to replace what would traditionally require multiple dedicated interfaces, improving versatility while maintaining JTAG standard compliance through proper signal sequencing and state management.
2Adaptability or versatility
If multiple access ports are provided in a device, then adaptability and testing flexibility are improved, but device complexity increases
Solution Approach 1:
The patent merges the functionality of multiple access ports into a single physical JTAG interface by using an Access Port Selector that multiplexes signals to different access port types. Instead of providing separate dedicated interfaces for each access port type (which would increase physical complexity), the patent combines them into one shared interface with selective routing, reducing the number of physical pins and simplifying the overall device architecture.
Solution Approach 2:
The Access Port Selector acts as an intermediary component between the external JTAG interface signals and the various access port types within the device. This mediator uses selection signals to route and configure the interface signals appropriately for the target access port type, enabling flexible access without requiring direct connections to multiple port types simultaneously, thus managing complexity through a centralized selection mechanism.
3Adaptability or versatility
If the JTAG interface signals are reused for non-JTAG access ports, then adaptability is improved, but measurement precision and signal integrity for JTAG-compliant operations deteriorate
Solution Approach 1:
The patent employs dynamic state management where the JTAG interface signals are placed in different functional states depending on the selected access port type. When accessing JTAG-compliant ports, the signals are configured with proper JTAG timing and sequencing; when accessing non-JTAG ports, the signals are reconfigured for the alternative protocol. This dynamic reconfiguration ensures that signal integrity and measurement precision are maintained for each specific operation type through appropriate signal edge detection and state synchronization.
Solution Approach 2:
The patent implements periodic state transitions and synchronization cycles to ensure proper signal integrity when switching between different access port types. The Access Port Selector uses clocked operations and state machines to periodically establish the correct signal conditions for the target port type before data transfer begins, ensuring that whether accessing JTAG or non-JTAG ports, the signal timing and synchronization are properly established to maintain measurement precision.
Data Source
AI summary
The disclosure describes a novel method and apparatuses for allowing a controller to select and access different types of access ports in a device. The selecting and accessing of the access ports is achieved using only the dedicated TDI, TMS, TCK, and TDO signal terminals of the device. The selecting and accessing of device access ports can be achieved when a single device is connected to the controller, when multiple devices are placed in a daisy-chain arrangement and connected to the controller, or when multiple devices are placed in a addressable parallel arrangement and connected to the controller. Additional embodiments are also provided and described in the disclosure.