Re: JTAG wiggler

Excellent Book:

Embedded system design on a shoestring : acieving high performance with
a limited budget / Lewin Edwards

Covers the use of the Macraigor JTAG wiggler!

Why don't you come and join my new group:
http://groups.google.com/group/realtime_signal_and_control

Frank

Tom Lucas wrote:
<learnfpga@xxxxxxxxx> wrote in message
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Tom Lucas wrote:
<learnfpga@xxxxxxxxx> wrote in message
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I am new to embedded programming and I am working on MPC8xx. What
exactly is JTAG wiggler and how will it help me with the
development?
I
tried to find info on it and most groups say that it speeds up
development process. Thanks in advance....

Google for Macraigor Wiggler.

First of all thanks for the response. I looked at that and the data
*** also but did not make much sense.

They never do until you find out what you wanted to know some other way
;-)

JTAG allows a direct interface to the heart of the processor and
access
to its pins so, with a suitable programmer you can program your
target
board but also see what is happening within it as the program is
running.

So for example I have a simple SPI driver for target board using
MPC8xx
but I am waiting for another board which will interface with my target
board. Till then will this wiggler help me to understand what the
program is doing and if its doing what it is supposed to do? Thanks
once again....

There are much better JTAG probes out there than the wiggler but they do
cost a bit more (£99 for Rowley's CrossLink and IIRC about £300 for
Segger's J-Link but the prices are on their websites). The better
probers use USB interface rather than the parallel port because
sometimes quite a bit of data needs to be moved about.

I think the reason the data *** is not much use to you is because you
are not too sure what the probe is for.

The first thing you can do with a probe is download your software into
your target board. Then, if you have debugging software then you can run
that code on your target and the probe gives you the power to stop and
start the target, set breakpoints (i.e. stop when a line of code is
reached in the program), examine the contents of registers and memory
and also to step through your code line by line.

The debugging software will most likely be a part of your compiler and
not of the Wiggler itself. The Wiggler will come with drivers that will
allow your debugger to communicate with it but, once you have that set
up, it shouldn't matter too much what type of probe you have - it is
just a link to the target.

If you don't have a debugger then you will have very little that you can
do with the probe - I don't know what compiler you are using so I can't
say more on that. You might even be using an assembler.

For your SPI application then (assuming you have a debugger) then you
can set a breakpoint after your routine to initialise the SPI interface
to allow you to stop and check all the appropriate registers have the
values you expect in them. You can then set breakpoints in your send and
recieve functions so that you can see when and if data is being sent or
received and if that data is what you expect. It will help you to
determine if you are at fault or the other guy.

Basically, once you see the possibilities of seeing which line of code
is being executed and what the target is doing then you will quickly
think of your own places in the code you want to test.

The difference in more expensive probes comes when you want to move
large chunks of data or keep log of data as it moves through the
processor. Some will put breakpoints into flash as well - which not all
probes can do.

.