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Unformatted text preview: than parallel access through the pins and performance testing at speed is not possible. The most promising production test methodology for macrocell based system chips appears to be to exploit the on-chip bus to give parallel access to the macrocell's periphery (especially where the macrocell has been designed specifically to give good access through this route). Multiplexing is used to give external access to peripheral macrocell signals that are important for performance testing and cannot conveniently be accessed via the on-chip bus, and the JTAG port is used to access other signals and internal state where necessary via scan chains. We have seen this approach as it is supported by ARM's 'Advanced Microcontroller Bus Architecture' (AMBA) which is described in Section 8.2 on page 216; the AMBA testing methodology is described on page 219. The JTAG system continues to be very important for board-level testing, and can also be used for in-circuit testing of the core logic and to access on-chip debug facilities. It is incorporated into most ARM designs and is an important component of their test and debug methodologies. 8.7 The ARM debug architecture
Debugging any computer system can be a complex task. There are two basic approaches to debugging, the simplest being based on watching a system from the outside using test equipment such as a logic analyser, and the more powerful being based on viewing a system from the inside with tools that support single stepping, the setting of breakpoints, and so on. Desktop debugging When the system to be debugged is a piece of software running on a desktop machine, all the user interface components are readily available and the debugger may itself simply be another piece of software running on the same machine. Breakpoints are set by replacing an instruction in the object program with a call to the debugger, remembering the original instruction so that it can be replaced when execution continues past the breakpoint. Often compilers have compile-time options to generate extensive debug information such as symbol tables whic...
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- Spring '09