Bob, what I have done on my DSP designs was to include a 14 pin
Header which permits access to the JTAG port.
There is plenty of information available but simply stated, below
goes a long ways. Thanks Alex.
Subject: jtag
Scott,
actually what JTAG really stands for is:
_ _ _ _
Just Try And Get information on me!!
Silly meanings aside (though I will explain why the above meaning is
very appropriate) all JTAG is, is just a fancy high speed serial port that
can talk to multiple devices (or TAPs).
What designers do on either side of this communication channel can vary
substantially. Originally I guess, the target was board functionality and
connectivity tests, but here are some other applications or variation
that I have been involved in the HDD segment:
1. Programming FLASH memory: We have developed a utility that
can program external FLASH devices via the JTAG port. The
technique used is to use the JTAG port to download the erase,
program & verify algorithms into block B0 of a fixed point DSP,
configure this as Prog memory and then transfer one small block at
a time (into RAM block B1) the object file to program into the flash.
2. Functional & Connectecvity Tests: Using the JTAG port and the
internal RAM of the DSP, we can download small test programs that
exercise the pins of the cDSP and configure external components to
perform functional and connectivity tests. In the HDD design that I
was involved in, we estimated that we could achieve 95% covergae
using this technique. To perform the same function by adding
boundary scan registers would have added significantly to the silicon
cost and software complexity.
3. Real Time De-Bugger: We are in the process of developing a high
level language de-bugger that allows the user to modify and view
target memory even while the DSP is executing. A monitor code
executing on the target system is required to process commands
from the de-bugger.
4. As A Speed Serial Port: There is a message passing register in the
fixed point DSPs with flags that can be used to transmit data back
and forth between a user interface and a target monitor. In many
embedded designs, users have been used to using an RS232 port as a
means of sending commands to the target hardware, doing some
data logging or just monitoring the state of the target. In the HDD
design that I was involved in, I simply said to the designers, "why
have the RS232 port at all, use the JTAG port instead, and write a
terminal program that talks to the target via the XDS510". Mind
you, the Real-Time De-bugger can be the same thing.
In all of the above applications, the JTAG port is simply a
communications channel (much like an RS232, RS422 or GPIB port) but
much fancier.
The real problem we have with JTAG, is that given the flexibility of
the standard and it's applications, the lack of co-ordination between
different departments using it, the lack of documentation detailing how
the guts of it work (in plain english) and the potential complexity of
the user software, we have shrouded the whole thing in mystery and
confusion.
So, I don't think that equating JTAG with EMULATION is strictly
correct given that it can be more than just emulation. I just simply
say "it's a fancy serial port".
Cheers,
Alex T.
mm
At 11:33 AM 5/24/99 -0700, you wrote:
**** Start of Attached Message(s) ****
Bob,
Texas Instruments has some good information on their site, www.ti.com ,
regarding JTAG and IEEE 1149.1. I don't have the specific pages, but a
search for JTAG should turn them up.
Regards,
Rick Thompson
Ventura Electronics Assembly
2665A Park Center Dr.
Simi Valley, CA 93065
+1 (805) 584-9858 voice
+1 (805) 584-1529 fax
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Bob Vanech
Sent: Monday, May 24, 1999 10:54 AM
To: [log in to unmask]
Subject: [TN] JTAG.??
To all...
I attemted to send this out Fri., but I don't
think it went. I'll try again. My boss asked me
if I knew anything about a "Board level testability
analysis including the role of and use of JTAG"? I
responded with an very educational DUH!!! Help,
does anyone know what this is about??? Any help
would be appreciated and thanks in advance.
Regards,
Bob Vanech
Mango Computers
(203) 857-4008 x108
**** End of Attached Message(s) ****
Mike Guenther [log in to unmask]
Stafford, Texas
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