Unformatted text preview: timing-accurate CAD environment, but software development can continue using the ARMulator-based model (probably moving up from cycle- to instruction-accurate timing for higher performance). In the course of the detailed hardware design it is likely that some of the timing assumptions built into the original software model prove impossible to meet. As the design evolves it is important to keep the software model in step so that the software development is based on the most accurate estimates of timing that are available. It is now common for complex systems development to be supported by multiple computer models of the target system built upon different levels of abstraction. Unless the lower-level models are synthesized automatically from the more abstract models, maintaining consistency between the models always takes considerable care and effort. 226 Architectural Support for System Development 8.6 The JTAG boundary scan test architecture
Two difficult areas in the development of a product based around an application specific embedded system chip are the production testing of the VLSI component and the production testing of the assembled printed circuit board. The second of these is addressed by the IEEE standard number 1149, 'Standard Test Access Port and Boundary-Scan Architecture'. This standard describes a 5-pin serial protocol for accessing and controlling the signal levels on the pins of a digital circuit, and has extensions for testing the circuitry on the chip itself. The standard was developed by the Joint Test Action Group (hence JTAG), and the architecture described by the standard is known either as 'JTAG boundary scan' or as 'IEEE 1149'. The general structure of the JTAG boundary scan test interface is shown in Figure 8.14. All the signals between the core logic and the pins are intercepted by the serial scan path which can connect the core logic to the pins in normal operating mode, or can read out the original value and replace it with a new value in test mode. Figure 8.14 JTAG boundary scan organization. The JTAG boun...
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This document was uploaded on 10/30/2011 for the course CSE 378 380 at SUNY Buffalo.
- Spring '09