JTRACE with ARM 7 and IRLEN = 3

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  • JTRACE with ARM 7 and IRLEN = 3

    I am using JTRACE with an ARM 7 core (MPU = NXP semiconductor LH79524). I have a single device on the JTAG bus and when I run JLINK I receive the following error message "Too few devices on the JTAG bus" "Count not find supported CPU core" Found 1 JTAG device, total IRLEN = 3: ID of device #0x00000000".


    IRLEN should be 4 clocks for an ARM 7 but checking with an oscillscope shows what appears to be the TDI waveform on the TDO output shifted 3 clock cycles instead of 4. Anyone have an idea what could cause this sort of behavior? JTAG waveforms look identical to what is shown in the start sequence on the JTRACE users guide except for TDO is shifted 3 instead of 4 clock cycles.


    When I use a logic product development LH79524 SDK board the same JTRACE mode works fine and has no problems initiializing and running properly on the SDK so I know the problem is my hardware but I do not know enough about JTAG to know if the 3 clock cycle delay instead of 4 cycles is a clue or not.