Difference between revisions of "JTAG explorer toy"
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[[Image:michai_015_board.jpg|thumb|'''Fig.6: 'after'.''' Finished toy-board. The funny thing is that when it's finished and toying has been done, it'll totally useless.]] | [[Image:michai_015_board.jpg|thumb|'''Fig.6: 'after'.''' Finished toy-board. The funny thing is that when it's finished and toying has been done, it'll totally useless.]] | ||
− | == | + | == What is this, and, why..? == |
− | + | I heard a lot about '''JTAG''', but never got to do anything with it, | |
+ | mainly because I CBA, and I didn't actually ''had to'' do anything with it. | ||
+ | |||
+ | This is of course bad, because... | ||
+ | <blockquote> | ||
+ | ''JTAG is '''THE SHIT''' - like [[:Image:Batman.jpg|Batman]]!'' | ||
+ | </blockquote> | ||
+ | ...or well, it's nice anyway. | ||
+ | |||
+ | === Disclaimer === | ||
+ | |||
+ | I interpreted the ATmega32-datasheet and (quite) some on-line docs as best as | ||
+ | I could; however, if there's a bug/flaw somewhere, let me know please. Note that | ||
+ | this thing is '''totally useless''', so questions/comments regarding will be | ||
+ | ignored. Xmas season, too much time, so there :-) | ||
+ | |||
+ | === Overview/summary === | ||
+ | |||
+ | The idea for me was to make a simple [[:Image:Michai_015_board.jpg|toy-board]] | ||
+ | with 2 MCU's on it -- one acting as JTAG host/master, and the other being | ||
+ | JTAG-victim. The PC talks to the master and slave through a serial protocol, | ||
+ | to read/set pins, and so initiate JTAG-actions; master talks to slave only through | ||
+ | its JTAG-port. The master itself is not JTAG-enabled, but drives/reads the slave's | ||
+ | JTAG-port I/O-pins. | ||
+ | |||
+ | === What I would like to see === | ||
+ | |||
+ | As I understood, JTAG offers a nice 'backdoor' into a (slave-)chip's state, and so that' | ||
+ | what I would like to see; I'd like to... | ||
+ | * put it in, and take it out of reset (reset/suspend/resume) | ||
+ | * read/set I/O pins, and decouple core logic from I/O pins (and drive them from [[:Image | ||
+ | * and some more, basically '''toy with it'''. | ||
+ | |||
+ | ---- | ||
+ | work in progress, tumdedum... |
Revision as of 18:05, 4 January 2009
Contents
What is this, and, why..?
I heard a lot about JTAG, but never got to do anything with it, mainly because I CBA, and I didn't actually had to do anything with it.
This is of course bad, because...
JTAG is THE SHIT - like Batman!
...or well, it's nice anyway.
Disclaimer
I interpreted the ATmega32-datasheet and (quite) some on-line docs as best as I could; however, if there's a bug/flaw somewhere, let me know please. Note that this thing is totally useless, so questions/comments regarding will be ignored. Xmas season, too much time, so there :-)
Overview/summary
The idea for me was to make a simple toy-board with 2 MCU's on it -- one acting as JTAG host/master, and the other being JTAG-victim. The PC talks to the master and slave through a serial protocol, to read/set pins, and so initiate JTAG-actions; master talks to slave only through its JTAG-port. The master itself is not JTAG-enabled, but drives/reads the slave's JTAG-port I/O-pins.
What I would like to see
As I understood, JTAG offers a nice 'backdoor' into a (slave-)chip's state, and so that' what I would like to see; I'd like to...
- put it in, and take it out of reset (reset/suspend/resume)
- read/set I/O pins, and decouple core logic from I/O pins (and drive them from [[:Image
- and some more, basically toy with it.
work in progress, tumdedum...