Talk:JTAG

message: Hi all,  nice job on the page so far.  Especially given much of the history is lacking on the web. Just tried to add a little bit of history.  Note that the security vulnerability section is a blatant advertisement.  All those links and mention should likely be taken out or limited to one sentence.  I will try to find more documents and links to history to help your page out.  Feel free to accept or modify anything I put in.  BTW, I did not work for Intel.  In fact, we were the ones who forced Intel into adding JTAG (NCR/Teradata Mainframe group) in 1990.  We built a 1024 processor supercomputer that year that had every IC and board on a JTAG scan system.  We could hot plug any board and test any internal chip or register while the system was online.  We even built PSR and CRC checks into a special JTAG control chip that was placed on each board.  Even the back plane was scannable!
SurplusGadgets 19:17, 22 May 2007 (UTC)
replies: text: Links are now pruned.  I'd be interested in seeing more info about “JTAG in the very-large&lrdquo; at some point, but as you noted, that stuff isn't very visible on-line, except maybe within certain IEEE working groups.  --69.226.209.34 (talk) 23:04, 2 October 2009 (UTC)

text: That should be a lot better now.  --69.226.209.34 (talk) 23:04, 2 October 2009 (UTC)

text: The state machine as printed by IEEE might have issues, but there are many versions around.  Nobody seems to have put an image into the wikipedia repository.  Personally, I suspect the state machine would be "too much detail".  It's certainly not necessary for anyone not doing very lowlevel work with JTAG, though it might be interesting.  69.226.238.251 (talk) 08:35, 26 November 2009 (UTC)

text: The state machine is a good idea I think as it forms the fundamental base of IEEE Std 1149.1 Boundary-scan Test Access Port And Architecture (aka JTAG). I will attempt to add it asap.Mapstain (talk) 10:29, 16 December 2009 (UTC)
thread_title:  General 

message: In general a very good article. BUT -
I have a bit of an issue with the statement "Primarily of historical interest: Intel's Pentium processors supported a "probe mode"[15] supporting JTAG access for debuggers. For a long time, its documentation was withdrawn by Intel. Current x86 processors appear to use JTAG only for boundary scan."
Both AMD and Intel have consistently supported full JTAG debug going all the way back to the original JTAG standard definition. Intel is a founding member of the JTAG MIPI group. JTAG vendors supporting JTAG debug on Intel architecture include Green Hills, American Arium, Wind River, Macraigor Systems, and Lauterbach. Most of these vendors focus in Intel Atom Processor, except for American Arium which tends to be the JTAG vendor of choice for client and server Intel Core and Xeon processors.
In addition Intel has it's own ITP-XDP3 JTAG device that is available as part of something called Intel System Studio and is also available with a restricted access advanced enabling product.
AMD similarly has a good ecosystem of JTAG vendors supporting their processors. Since the JTAG implementation of AMD differs from that of Intel the ecosystem vendors offering support are different as well, although there is some overlap.
With the heightened need for platform security JTAG is frequently disabled on production silicon, but that is true for many ARM processor SKUs especially in mobility and telephony as well.  
The only other limitation I see compared to ARM is that most of the x86 JTAG devices fall into the higher cost bracket. The options for the hobbyist or small scale system integrator are limited.
I am willing to make the appropriate changes to this Wikipedia entry, if this is the general consensus.  — Preceding unsigned comment added by Roboima (talk • contribs) 16:32, 23 June 2013 (UTC)
thread_title:  x86 

message: Can somebody take a pictures of a JTAG cable, connector, and/or port to add to this?  Also, would an eye pattern be useful here? --W0lfie (talk) 14:59, 21 December 2007 (UTC)
thread_title:  Picture(s) 

message: :"The optional IDCODE instruction, with an implementor-defined opcode. IDCODE is associated with a 32-bit register (IDCODE). Its data uses a standardized format that includes an IEEE manufacturer code, a manufacturer part number, and a part version code."
Is there a central database for all IDCODEs? Does this IDCODE have something to do with IEEE's Organizationally Unique Identifier? --Abdull (talk) 16:51, 14 March 2010 (UTC)
replies: text:  Hopefully now clearer. Ptoboley (talk) 10:11, 24 May 2010 (UTC)
thread_title:  IEEE manufacturer code 

message: In the article, the following is stated: "The BYPASS instruction, opcode all ones regardless of the TAP's instruction register size, must be supported by all TAPs. It is associated with a single bit data register (also called BYPASS) which always reads as zero." I need clarification here because I after reading about JTAG, I understand that the BYPASS instruction will "connect" a 1 bit shift register (FF) between TDI and TDO. Then the statement "...which always reads as zero." is not true.
It might be that at start-up or upon selection (could someone confirm this as I do not have the IEEE Standard available) the BYPASS register will always read zero but then it will read whatever TDI value was on the previous clock cycle. 
Pelgv (talk) 22:28, 16 March 2010 (UTC)
thread_title:  JTAG Instructions 

message: This name has been added recently by an untracable agent. The name is not known to me in connection with JTAG so I am 
keen to know more about this person. Another Harry, Harry Bleeker, certainly chaired the JTAG committee for some years.
Is this a point of confusion ? Or, can someone enlighten me.
Mapstain (talk) 16:46, 20 April 2010 (UTC)
thread_title:  Harry Wardrop 

message: All information from Wiggler (JTAG) has been merged into this article. Northamerica1000(talk) 15:19, 9 July 2012 (UTC)
replies: text: I removed the Wiggler information. Parallel port interfaces were mentioned above (and limitations were cited). The tone sounds like it is advertising a product. Other information about the Wiggler is tangential to JTAG. Glrx (talk) 15:26, 10 July 2012 (UTC)
replies: text: Unbuffered Wiggler is so popular among hobbysts that it really should be mentioned here. The popularity comes from its practically zero cost to build compared to regular JTAG adapters which can easily cost more than US $100.  — Preceding unsigned comment added by 212.160.172.85 (talk) 10:41, 27 April 2017 (UTC)
replies: text: The Wiggler might have been important at one time, but not anymore because few new computers have a parallel port in 2017.  Today, a person can easily find a cheap JTAG device, and much cheaper than USD$100.  Still there should added to an open-source section, along with some others.  • Sbmeirow • Talk • 09:54, 28 April 2017 (UTC)
thread_title:  Merger complete 

message: Dear engineers. Please add section about copyright, license, and fees for use (if any). Ideally the article should contain exact information about these, and also about limitations for free use, patenting, and other issues for use in DIY and other open environments. Or, if no such limitations, it must be clearly stated. Thanks.  — Preceding unsigned comment added by 85.31.112.107 (talk) 07:43, 26 March 2014 (UTC)
thread_title:  License 

message: My brain is fried right now, but I think there is more depth to the history. At some point, James B. Angell at Stanford proposed logic testing using serial scans. IBM came out with Level-Sensitive Scan Design (LSSD) for testing its computers. Then there was JTAG. Glrx (talk) 17:10, 1 April 2015 (UTC)
thread_title:  History 

message: I just now noticed the renaming of this article.  Though JTAG does make sense, there are cases for alternate names, per other articles on Wikipedia, which also has weight in the naming of this article.  I know there are more, but these are the ones that I remember.  • Sbmeirow • Talk • 21:22, 25 April 2016 (UTC)
replies: text: Unlike FireWire and WiFi, this standard does not seem to be as well known by its number (and we do have articles on ZigBee and WiFi as well). And as was noted above, in this case the long form of the acronym is somewhat misleading (just as is the case with e.g. JPEG). —Ruud 23:50, 25 April 2016 (UTC)
thread_title:  Article Name 

message: As of the current version, there is a passage which says Serial Wire Debug (SWD) is an alternative 2-pin electrical interface that uses the same protocol.
I think there are two clarifications missing:
# Same protocol as what? I can't be referring to JTAG, as JTAG ist not a protocol: "The JTAG specification doesnt even define the protocol for how data is passed between debugger and debugee." 
# SWD is an own protocol, which serves the same purpose as JTAG, but is not using it in any form.
--2003:F7:5BC0:1F00:B14F:45B1:4815:D277 (talk) 19:11, 12 December 2019 (UTC)
thread_title:  Serial Wire Debug