Reset ARM7 with Clock on XIN Only (XOUT Floating)

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  • Reset ARM7 with Clock on XIN Only (XOUT Floating)

    I am using an Atmel AT91SAM7S-EK development board, a SAM-ICE JTAG emulator marketed by Atmel (but made by Segger), and IAR (version 5.0) as my IDE. The schematic for the devlopment board can be found here:

    In our design, we have a 26MHz clock input on the XIN pin of the ARM7 with XOUT floating instead of using a crystal oscillator. On the development board, the crystal was removed and I am using a signal generator to provide the clock on the XIN pin. This is the only change to the board. This setup appears to work and the system is stable.

    The issue I am seeing is when resetting the ARM7 from within the IAR IDE. If I manually set the ARM7's clock select register (field CSS in the PMC's MCKR register) to run off of its internal clock before I force a reset, everything works as expected. If I do not select the internal clock and leave the ARM7 running off of the input clock on XIN, I receive numerous errors and IAR quits the debug session. The errors relate to not being able to halt the ARM7 core and being unable to read memory correctly.

    I have contacted IAR regarding this issue, but they believe it is caused by the JTAG emulator. This issue also exists on our current design boards, which use the same JTAG circuitry as the development board.

    Any help, thoughts, or suggestions regarding this would be appreciated.