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Problems using Tiva Launchpad to debug an external processor

chris walck
Prodigy 10 points

Other Parts Discussed in Thread: TM4C123GH6PM

Hi,

I am working on designing a pcb around the TM4C123GH6PM microprocessor.  my first prototype had a the Tiva Launchpad plugging straight into the board, and now I am looking to integrate.

I am trying to make sure I can use the launchpad ICDI to debug the external processor before moving forward, and am having some trouble.  currently I have the TM4C123GH6PM chip broken out on a breadboard with the supporting circuitry around it as shown in the Tiva Launchpad manual, page 21, component U1-B.  found here:

http://www.ti.com/lit/ug/spmu296/spmu296.pdf

The only differences with my setup are that I have a couple slightly different capacitor sizes across VDDC and GND, and VDD/DBAT/VDDA and ground.  I am also just pulling WAKE up with a 10K resistor.  Both oscillator circuits and reset button are the same.  I am powering the processor using 3.3V from the launchpad.  I also have the following connections from my launchpad to my microprossor:

Launchpad pin, TCK to pin 52

Launchpad pin, TMS to pin 51

Launchpad pin, TDO to pin49

Launchpad pin, TDI to pin 50

I also have EXT_DBG grounded on the launchpad, and the power jumper removed.

according on the wiki, this should work, but when I hit "debug" on CCS, I just get an "error connecting to the target" message.

is there anything I am missing here?  Am I correct in assuming that I can use Code Composer Studio in this way?

any help on this matter would be greatly appreciated,

thanks,

Chris

  • 0
    Guru 117855 points

    chris walck said:
    is there anything I am missing here?

    Our group does not favor nor use CCS nor launch pads - but have vast experience w/JTAG & newer/better SWD - to debug & program ARM MCUs.

    You present here with a new MCU board and (perhaps) the first time, attempted use of a launch pad (pressed) into service as a JTAG debug/program pod.  Such brings, "more variables" than our group is comfortable with - to any new design effort.  We simply do not know if your new board - or the launch pad as JTAG pod - or both, together - cause your issue...

    If you have - or can quickly acquire - a 2nd launch pad - you may attempt to debug/program it - employing your existing, "launch pad as JTAG pod" implementation.  (which presently is reported as "failing" when connected to your custom board)  Base this suggestion on the (very strong) belief that a new launchpad is more likely to be "correct" than any custom (first time check-out) board.  (no knock upon you implied/intended - that's just reality...)

    Should the 2nd launch board succeed when so attached - your focus may (rightly) shift to your custom board.  If so - I'd better detail the "degree of deviation" of those "slightly different capacitor sizes (sic) values" and the presence of JTAG pull-up resistors.  (we always use external R's - and our JTAG/SWD ALWAYS works! {some 10K+ boards})

    Limiting the size - and focus - of your "battlefield" works during war - the courtroom - and during MCU conflicts - too...

  • 0
    TI__Guru**** 244440 points
    Hello Chris,

    TM4C123GH6PM on a bread board does not sound a good idea. The whole ground and power plane beneath the device, cap's and oscillators may be too much for the device & debugger to handle (unless some one very experienced with TM4C on a BB).

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 117855 points

    Amit Ashara said:
    TM4C123GH6PM on a bread board does not sound a good idea.

    Agreed - yet we've seen that work - even w/faster ARM MCUs.  (and as you note - great care, attention to detail, required)

    Believe both your caution - and my suggestion, "Minimize the number of UNKNOWNS in Play" during intial test/verify/check-out should be heeded by poster and follow-on readers...

  • 0
    Guru 27285 points

    chris walck said:
    I am working on designing a pcb around the TM4C123GH6PM microprocessor.  my first prototype had a the Tiva Launchpad plugging straight into the board, and now I am looking to integrate.

     A picture of your test can help understand what is this and if it can work too... Otherwise trouble appear to come from other sources.

    chris walck said:

    I also have EXT_DBG grounded on the launchpad, and the power jumper removed.

     This pin serve not to debug an external board but to access INTERNAL cpu disabling JTAG port of ICDI so you can use EXTERNAL debugger interface, so remove this ground and retry.