Software Debug

Discussion on the justification for SJTAG in each of the identified Use Cases: Alternatives, cost benefits and penalties
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Bradford Van Treuren
SJTAG Chair Emeritus
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Software Debug

Post by Bradford Van Treuren » Fri Jul 25, 2008 8:45 pm

Meeting Minutes reference:
http://www.sjtag.org/minutes/minutes080630.html


The software debug use case has many facets covering many overlaps with other use case examples while opening up the opportunity to begin to bridge the gap between structural test and functional test. My personal view is the tooling for software debug has not progressed as far as the user's needs have expected. Emulation technology has suffered greatly from the same tooling problems plaguing other 1149.1 based tools - the lack of support of other vendor hardware in the chain. Recently, that issues has been vanishing for some tool provders, but not for the majority. To compound the problem, the emulation interfaces between the various processors are not compatible. Further, these interfaces, which claim to be based on IEEE 1149.1 and use the JTAG port to access the internal registers, extend the interface to require additional signals to be able to work. Hopefully, IEEE P1149.7 will be able to resolve some of these problems. Third, the emulation interface is only able to be activated following a reset of the processor. There are some processor designs appearing which allow read only access to the state of the registers within the processor while not in direct emulation mode. I feel this is the trend that must be achieved in order to make this use case useful for the future of system testing in the field and system integration product stages.

Due to the need for additional signals to augment the JTAG in current emulator interfaces, it is difficult to gain access to these signals from a system level. This is especially true if there are multple processors on a board that need to have access from an emulation interface (DSPs, CPU cores in FPGAs, multiple CPUs). Further, the use of gateway multidrop devices at the system level tends to break interfaces from emulation tool providers.

An activity where the emulation environment is playing a larger role in manufacturing test is the area of performing supplimental functional test via the emulation interface. Some 1149.1 tool vendors are now beginning to provide integrated solutions with their tools to provide a set of canned functional tests that cover portions of the circuit which are not covered with straight 1149.1. Certain types of emulation based tests may also be able to test a circuit at speed - something that 1149.1 is unable to solve.

I see this use case as one in its infantcy regarding system test and is one that will play a more important role as processor access issues are resolved. These issues are certainly a topic the SJTAG intiative team needs to be investigating.

The discussion thread in the meeting minutes starts with 2008-06-30.
Last edited by Ian McIntosh on Thu Jun 11, 2009 7:09 am, edited 1 time in total.
Reason: Added link to meeting minutes
Bradford Van Treuren
Distinguished Member of Technical Staff
NOKIA MN

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