Shadow Access Port Circuit for Extending JTAG TAP Functions
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Solution Overview
Problem
Existing IEEE 1149.1 JTAG TAP interfaces in electrical devices require manual modification or redesign to support additional operations like debug, trace, and programming, which is a cumbersome and time-consuming process.
Innovation Solution
A Shadow Access Port (SAP) is integrated with the IEEE 1149.1 TAP to extend its functionality without altering the existing TDI, TCK, and TMS signals, allowing seamless operation alongside the TAP and enabling additional operations like debug, trace, and programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If manual modification or redesign is performed to support additional operations, then functionality is extended, but device complexity and development time increase
Solution Approach 1:
The patent divides the access port functionality into two separate entities: the original TAP and the new SAP. Each has its own state machine, instruction registers, and data registers. This segmentation allows independent operation and eliminates the need to modify the original TAP design, thereby extending functionality without increasing overall system complexity.
Solution Approach 2:
The SAP is designed as a universal access port that can perform multiple operations including debug, trace, and programming functions. By creating a multi-functional SAP that can handle various operations through its state machine and register structures, the patent extends the device's capabilities without requiring separate dedicated circuits for each function.
2Adaptability or versatility
If manual modification or redesign is performed to support additional operations, then functionality is extended, but development time increases
Solution Approach 1:
The SAP is designed with pre-defined state machines, instruction registers, and data registers that are prepared in advance. The state machine includes pre-configured states for different operations (debug, trace, programming), and the register structures are predetermined. This preliminary design allows the SAP to be integrated without requiring time-consuming manual modifications during the development phase.
Solution Approach 2:
The SAP is essentially a copy of the TAP architecture with similar state machine, instruction register, and data register structures. By replicating the proven TAP design patterns in the SAP, the patent enables rapid development without needing to create new designs from scratch, thereby reducing development time while extending functionality.
3Device complexity
If existing TAP interface signals are reused, then signal count is reduced, but signal contention and interference may occur
Solution Approach 1:
The patent implements periodic action by having the TAP operate on the rising edge of the TCK clock signal while the SAP operates on the falling edge of the TCK clock signal. This alternating timing scheme allows both access ports to share the same physical signals (TDI, TCK, TMS, TDO) without signal contention, as they are active during different time periods within each clock cycle.
Solution Approach 2:
The patent introduces dynamic control through enable signals (TEN for TAP, SEN for SAP) that dynamically activate or deactivate each access port based on operational requirements. The output circuit dynamically selects which port's data to output based on which port is currently active, thereby managing signal sharing dynamically and preventing interference while maintaining reliability.
Data Source
AI summary
The disclosure describes a novel method and apparatus for providing a shadow access port within a device. The shadow access port is accessed to perform operations in the device by reusing the TDI, TMS, TCK and TDO signals that are used to operate a test access port within the device. The presence and operation of the shadow access port is transparent to the presence and operation of the test access port. According to the disclosure, the shadow access port operates on the falling edge of the TCK signal while the test access port conventionally operates on the rising edge of the TCK signal.