The original JTAG standard provided a real leap forwards in testing, but as many designs moved away from conventional printed circuit boards to multi-chip modules, stacked die packages,and further testing and debug was required, including under power down and low power operation, an addition to the original JTAG standard was needed. The resulting IEEE The new IEEE Equipment conforming to the IEEE
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A description of the boundary scan description language was added in Complications arose as chips increased functionality and designs shifted away from PC boards to multichip modules and stacked die packages.
These difficulties included handling the pin count requirements and multiple Test Access Port TAP controllers for System-on-Chip SoC devices, testing multichip modules and stacked die configurations, enhancing debug performance, and improving test and debug logic power-down in low-power conditions. Their work laid the foundation for the IEEE This provides new scan topologies that are favorable to stacked die and multichip module configurations and offers advanced capabilities to aid in software debug.
IEEE In addition to creating a control system, this class addresses the needs of power-sensitive devices with four power-down modes. The key innovation is the combination of the IEEE Table 1 Commands are typically bit values and consist of two consecutive DR scans while the controller is locked at Control Level 2. Command Part 1 CP1 provides a 5-bit operating code, and Command Part 2 CP2 provides the immediate operand, which is the lower 5 bits of the command.
The function specified by the command is performed when CP2 completes. Each of the three three-part commands has a special purpose. Class T2 To achieve higher performance for engineers involved in testing high chip count applications, Class T2 offers a chip-level bypass mechanism that shortens scan chains and another mechanism that provides hot connect capability.
This protects TAPs from spurious signals and prevents core corruption during hot connections. The mechanism also functions as a firewall, enabling access to chip TAPs only after a predetermined sequence is initiated. This security measure ensures that only a debug test controller can access the system once a running, powered target has a stable electrical connection. A write-only register used to specify the scan format and a device address assignment for star configurations also have been added to the new standard.
Star topology is desirable for stacked die configurations because the location of the debug connection is consistent. Whereas Figure 2a shows the series scan topology, Figure 2b illustrates the Star-4 or Wide Star configuration.
Figure 2 IEEE To operate in this mode, chips in the star configuration must be assigned Controller Identification CID numbers. An iterative arbitration system is used to assign CIDs, and operations are executed using Control Level 2. Class T4 To address the rising number of pins in SoC devices, Class T4 adds scan formats to support transactions with two pins instead of four, resulting in fewer total pins required on chip packages. This also helps with stacked die configurations because it is highly desirable to have the fewest number of connectors possible when die are stacked.
This is the Star-2 configuration shown in Figure 3. Figure 3 Besides reducing pin count, Class T4 defines optimized download-specific scan modes in which only useful information is downloaded.
To improve pin operation performance, the clock rate also can be doubled. These features combined with the optimized transactions do not cause performance loss, instead improving performance in some cases. This class gives the test port the ability to perform debug and instrumentation operations concurrently data is transferred during idle time , which reduces the number of pins dedicated to instrumentation, and enables custom protocols to use the pins, a feature many vendors offer in nonstandard ways.
Class T5 standardizes the process to access the pins. Stephen Lau is the product manager for emulation technology at Texas Instruments, based in Dallas, Texas. His responsibilities include the definition of on-chip debug technology and associated emulator products deployed through third-party partnerships. He is also responsible for marketing IEEE Texas Instruments.
IEEE 1149.7: Expanding and improving JTAG
A description of the boundary scan description language was added in Complications arose as chips increased functionality and designs shifted away from PC boards to multichip modules and stacked die packages. These difficulties included handling the pin count requirements and multiple Test Access Port TAP controllers for System-on-Chip SoC devices, testing multichip modules and stacked die configurations, enhancing debug performance, and improving test and debug logic power-down in low-power conditions. Their work laid the foundation for the IEEE This provides new scan topologies that are favorable to stacked die and multichip module configurations and offers advanced capabilities to aid in software debug.
This results in a 1-bit path being created for Instruction Register and Data Register scans. It adds support for up to 2 data channels for non-scan data transfers. These can be used for application specific debug and instrumentation applications. Classes T4 and T5 are focussed on the two pin system operation rather than the four required for the original JTAG system. One of the main elements is that the focus of JTAG testing has been broadened somewhat.
IEEE 1149.7 STANDARD PDF
IEEE While IEEE Backward compatibility is maintained so that any board or system that integrates chips that support either standard is amenable to test or debug procedures. Benefits The new standard offers embedded designers several benefits, including: The ability to control debug logic power consumption in an industry standard way.