An SJTAG Green Paper

By Bradford G. Van Treuren, SJTAG Chair Emeritus

(Full size images may be viewed from the gallery at the foot of this article. A description of SJTAG Green Papers can be found here.)

Abstract

In this paper, I plan to present a comparison and contrast to the issues of chain selection as used by several well known use cases for board level testing.  During the formation of the IEEE 1687 standard draft, there was much debate regarding whether the test engineer should be responsible for configuring the topology of the scan chain inside of a device or should the tooling be able to automatically configure the topology based on what actions were being applied to the hardware.  On one side, engineers like to be able to have control over tools to give them a way to override assumptions a tool uses for cases where they do not match the desired behavior.  Further, engineers have to deal with board and chip designs that do not always comply with a given standard. On the flip side, topologies are getting quite complex and it is difficult and time consuming for an engineer to map out and configure the appropriate topology for a given set of actions.  This is especially true for actions requiring the selection of different instruments residing down separate hierarchical trees inside of a device.  Power management inside devices today complicates this problem even further.  If too many methods for selecting a topographical path through a device are used, it becomes a very difficult task for tools to be able to model the sequences that have to be performed in order to select or deselect a particular path.  This is even more difficult as you move up in the hierarchy to the board and system levels.

An SJTAG Green Paper

By Bradford G. Van Treuren, SJTAG Chair Emeritus

(Full size images may be viewed from the gallery at the foot of this article. A description of SJTAG Green Papers can be found here.)

Abstract

Looking at an entire system to understand the complexity of control and test operations is a daunting task.  Decomposing the problem into smaller pieces does not always provide insights unless one is able to discover commonalities between these levels.  A key insight for SJTAG is the realization that the lowest common denominator for all test and control points in the problem domain is the basic Test Data Register (TDR).  This primitive follows the basic constraint supporting a serial shift protocol implementing a Capture-Shift-Update (CSU) strategy as defined by the IEEE 1149.1 TAP state machine.  Important discoveries is that other control protocols used for system test and configuration (e.g., I2C, SPI, memory mapped) are able to support this same CSU protocol either directly or indirectly using these other interfaces.  How the data is passed through a communication channel down to a TDR is controlled by the AccessLink defining the control aspect of the data and the DataLink that is responsible for transporting the data through that AccessLink.  These concepts for the system and board domains are described in this Green Paper.

Well, almost "All" New! Throughout October, we've been working in the background to refresh and enhance the Group's web presence with a range of new features.

The process for reaffirmation of the group's officers for 2014 was conducted in late February and the results of voting, recorded in the minutes of the March 3rd meeting, saw the re appointment of both Ian McIntosh as Chair and Heiko Ehrenberg as Vice-Chair.

Revalidation of Newsletter Subscribers

We have been producing our newsletters for almost five years and in that time it's almost inevitable that some of our readers will have moved on to other things, so it's maybe about time that we cleaned up our mailing list to ensure that we're only sending this to people that still want to receive it.

Subcategories

Pages for 2009 Survey results.