I just ran into the following FAQ and info that might be of help:
a JTAG FAQ: http://hri.sourceforge.net/tools/jtag_faq_org.html
interesting detail:
TAG specification is in Std IEEE 1149.1 (costs about $100). I don't
have it. Please search at internet for some JTAG related documents.
This is good: http://www-s.ti.com/sc/psheets/ssya002c/ssya002c.pdf
also:
You just have to write software to go through the states of JTAG FSM
(here is the state diagram of this FSM:
http://www.inaccessnetworks.com/projects/ianjtag/jtag-intro/jtag-state-machine-large.png).
TCK and TMS are used to go through the states of FSM. And TDI is used
to serially send through this interface your commands and data to JTAG
controller on the IC (in your case, to the ARM uC) and read back reply
through the TDO pin. The only problem is that some companies do not open
all details about available custom JTAG commands (JTAG standard defines
only 2 necessary commands: EXTEST and SAMPLE and some optional commmands
like INTEST, BIST and others). For example, Texas Instruments do not
give an access to the description of commands that are used for
In-Circuit Debugging of their TMS DSPs. Instead of, they sell this JTAG
ICD with simple software for about 1000$!!! Nice business - such a price
for 4 wires and some I/O ICs! ;-)
Hope this helps.
EBo --
