JTAG on embedded platforms

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Roman Mashak Contact options for registered users 's Avatar (by Gravatar) posted on
August 23, 2008, 9:15 pm
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Hello,

I don't quite understand -- is it necessary to have a specific JTAG device
for every specific board or it may be generally used on a variety of
platforms. As I see, it is standard, so as long as a development board or
chip is JTAG-conformant, any JTAG may be used with any platform. Or the
other way, it's chip specific and entirely depends on manufacturer?

Thanks in advance for clarifying this.

Best regards, Roman Mashak



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Mariusz Koniarz Contact options for registered users 's Avatar (by Gravatar) posted on
August 23, 2008, 5:37 pm
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Re: JTAG on embedded platforms
Hello.

I'm not sure but....
there could be 3 different answers..
1.  JTAG is standard and while You think about basic functions like
boundary scan, then
Yes, any JTAG should work with any board. (sometimes different connector
or pinouts & Vcc level).

2. Partially Yes, while you think about  microcontrollers e.g. ARM7 or
ARM9, from several manufacturers.
basic debugging should work (e.g openocd&gnu tools & Eclipse) but flash
programming is manufacturer dependend.
And of course different boards must have different flash programming
commands. e.g in-chip flash vs external.

3. No. JTAG is also used for FPGA, AVR, MIPS and many other devices - then
You should have a several different JTAG devices.

Hmm, not true. Maybe single hardware would be sufficient but
software&drivers different for sure.


I recently bought this:
http://www.avrfreaks.net/index.php?func=viewItem&item_id78%7&module=Freaks%20Tools
<http://www.avrfreaks.net/index.php?func=viewItem&item_id78%7&module=Freaks%20Tools
single device - swith jumper and You have different JTAG.

Maybe manufacturer is going to add more supported targets in future? Try
ask.
It works perfect for me. (I use that "USB JTAG A1" device for AVR ISP,
AVR JTAG, ARM7 JTAG, ARM9 JTAG & FPGA JTAG) - it have 4 different
connectors.

So, If You want universal JTAG device,  maybe there is already another
universal JTAG device even more powerfull? Google is Your friend.



M.K.





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