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ARM: JTAG problem on developed ARM board

Discussion in 'Embedded' started by Mad I.D., Sep 18, 2009.

  1. Mad I.D.

    Mad I.D. Guest

    I designed an ARM7 board with LPC2478 MCU. Unfortunately, JTAG doesn't
    work like one would expect.

    I can download code to FLASH, I can start debugging, BUT every time it
    comes to the first STR instruction I get "Could not stop device"
    ERROR. When I don't step the code it goes to some garbage address.

    I have ONLY ONE physical pull-up/down resistor on my JTAG 2x10
    connector (device is ULINK(non2)).

    TCK is pulled to +3.3V with 10k resistor.

    Signals DBGEN, TMS, TDI, nTRST, RTCK are terminated inside LPC2478.

    I saw on some boards that TCK is pulled down? Is this the source of my
    problem ?

    Mad I.D., Sep 18, 2009
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  2. Mad I.D.

    Rich Webb Guest

    Maybe. What other NXP ARM devices have you used? If you've been
    comfortable with the 21xx-series, and basically imported your
    initialization steps from working code for those chips, then you may be
    missing some details that have changed with the 24xx and are not really
    running with the clock speed you think you're running at. That can throw
    off the JTAG link and lead to unexpected behavior.
    Rich Webb, Sep 18, 2009
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  3. Mad I.D.

    Leon Guest

    You probably need more resistors on the JTAG interface - see the ARM

    Leon, Sep 18, 2009
  4. Mad I.D.

    Leon Guest

    Sorry, it has internal pull-ups as you mentioned.

    Leon, Sep 18, 2009
  5. Mad I.D.

    Tauno Voipio Guest

    IIRC, the JTAG lines should be all pulled up
    with suitable resistors.

    Are you sure that there is not an undesired
    connection from WR- to some weird place on
    the board?

    Did you configure the debugger for ARM7TDMI-S?
    Tauno Voipio, Sep 20, 2009
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