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JTAG/Boundary Scan



Jan 1, 1970
Has anyone ever used this method for field troubleshooting?


Jan 1, 1970
"Michael A. Terrell" wrote in message

Has anyone ever used this method for field troubleshooting?

How do you propose using the programming interface to troubleshoot
something? Are you going to write custom software and reprogram the
processor? What software and interface do you have, and is it
appropriate for the CPU involved? I programmed various embedded
controller boards for four years with JTAG, but there was no way to
troubleshoot the board from that port. Boundary scan is for testing the
CPU, not the rest of the board.

Not proposing anything. Asking a question. Not a good idea here, these

D Yuniskis

Jan 1, 1970
HI Charles,

Has anyone ever used this method for field troubleshooting?

I doubt you will find anyone using a *raw* JTAG i/f in
this way. You would need far too much information about
the devices involved, their interconnects, etc.

When *designing* a product, careful consideration to the
JTAG abilities of the device(s) you use can help bring *up*
a system (virgin hardware) by giving you control over
nodes that would otherwise be difficult to manipulate.
Many MCU's also use JTAG to program onboard memory and/or
a crude software debugging interface.

But, unless the manufacturer has specifically designed a tool
that hides all of this detail from you and reduces it to
a set of indicators (or, perhaps, an interface to software
running on a laptop), chances are, it won't be of much
practical use (though it is often used to "hack" or
"repurpose" existing devices despite the manufacturer's
original intent).

Some products will bring JTAG pins out to an (undocumented)
connector. Or, they'll be microprobed in production (to
save the cost of the connector :> ). Similarly, many products
have "free" serial ports that are routed (and often have
interesting capabilities! :> )

But, JTAG isn't as nice and semi-standardized as OBD, OBD-II,
etc. for automobiles... too many variables to account for.



Jan 1, 1970
"Charles" wrote in message
Has anyone ever used this method for field troubleshooting?

Hey Dave Platt and D Yuniskis ... thanks!

Seems that the promise of JTAG for field service has fallen by the wayside,
for troubleshooting and repair at least. It is used for firmware upgrades.
Economics rule!


Jan 1, 1970
I see that no one bit on your duplicate post on
Yup, not a single reply. Not surprised.

Most designs don't have enough spare flash for any diagnostics. It
isn't worth the trouble for anything outside a factory where an
automated test fixture can test the entire board without being
reprogrammed. Not what you want to hear, but it's the truth. The
'boundary' stops at the I/O pins where it was intended to. It was a way
to test a complex processor with limited tools, not an entire board.

I am guessing that the up-front costs for field service cannot be justified
(sold to management). Other than flash upgrades, it appears to be an
unfulfilled promise (pipe dream?) as far as field service is concerned.