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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Post by Bradford Van Treuren »

Meeting Minutes reference:

This topic is similar to the role of the Programming/Updates use case, but is targeting a very different set of system features. For Programming/Updates, the target is a programmable device to change its logical behavior (e.g., its design structure). The Configuration/Tuning/Instrumentation use case involves programming of functional features within the system. This primarily consists of various forms of instruments built into devices which control functions like power conditioning, temperature monitoring, and even overlaps aspects of BIST control. The IEEE P1687 working group is actively pursuing IEEE 1149.1 solutions for interfacing to these instruments in a standardized form to allow for more automation of instrument control in the future. Once this standard is adopted, I can see this use case becoming more important for the system level as many of these instruments are also accessible from the system interface. Moreover, since these instruments are managing more functional aspects of the system, this use case might be required for normal system operation and setup/configuration.

Traditionally, people have been using many other mechanisms in their system to provide the same interface capability to the instruments. The most prominent one is the I2C interface. The justification for P1687 is that most of the devices containing instruments already support 1149.1 testing to support manufacturing test, that it makes sense to support a single interface access mechanism to the features inside a device. Thus, the designer would not be required to support both an 1149.1 interface and an I2C interface to the device.

The greatest challenge to be faced for this use case is the issue of tool vendor support. Of the instrumentation already supported by 1149.1 based tools, most vendor tools are unable to support other vendor devices in the same scan chain. This is the same pattern other tooling industries followed when introducing their new technologies. It is a matter of educating the tool/device vendors to the need to support a variety of devices on the same chain. It is also imperative that users of these devices place these requirements on the device vendors and tool suppliers to support these features.

The initiative team has been discussing this use case starting with the 2008-05-12 meeting. Please view the meeting minutes for some interesting dialog on this subject.
Last edited by Ian McIntosh on Thu Jun 11, 2009 7:03 am, edited 1 time in total.
Reason: Added links to meeting minutes
Bradford Van Treuren
Distinguished Member of Technical Staff
VT Enterprises Consulting Services