4.8.4. DAP transfers

This section describes:

DAP transfer aborts

The AHB-AP does not cancel the system-facing operation and returns dapready HIGH one cycle after dapabort has been asserted by the driving debug port. The externally driving AHB master port does not violate the AHB protocol. After a transfer has been aborted, the CSW Register can be read to determine the state of the transfer in progress bit, TrInProg. When TrInProg returns to zero, either because the external transfer completes, or because of a reset, the AHB-AP returns to normal operation. All other writes to the AHB-AP are ignored until this bit is returned LOW after a transfer abort.

Error response generation

This section describes:

System initiated error response

An error response received on the system driving master propagates onto the DAP bus when the transfer is completed. This response is received by the debug ports.

AHB-AP reads after an abort

After a dapabort operation is carried out, and an external transfer is still pending, that is, the TrInProg bit remains HIGH, reads of all registers return a normal response except for reads of the Data read-write Register and banked registers. Reads of the Data Read/Write Register and banked registers return an error response because they cannot initiate a new system read transfer until the CSW.TrInProg is set to 0 either by completing the system transfer or by a reset.

AHB-AP writes after an abort

After a dapabort operation is carried out, and an external transfer is still pending, that is, the transfer in progress bit remains HIGH, all writes to the access port return an error response, because they are ignored until the TrInProg bit is set to 0.

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