9.8.3. Message transfer

Message transfer from the debugger to the processor is carried out in a similar fashion:

  1. The debugger polls the R bit of the Debug Comms Control register:

    • If the R bit is low, the Data Read register is free and so data can be placed there for the processor to read.

    • If the R bit is set, previously deposited data has not yet been collected and so the debugger must wait.

  2. When the Comms Data Read register is free, data is written there via the scan chain. The action of this write sets the R bit in the Debug Comms Control register.

  3. When the processor polls this register, it sees an MCLK synchronized version.

    • If the R bit is set, this denotes that there is data waiting to be collected, and this can be read via a CPRT load. The action of this load clears the R bit in the Debug Comms Control register.

    • If the R bit is clear, this denotes that the data has been taken and the process may now be repeated.

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