2.7.4. 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 Control/Status Word 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.

Access port initiated error response

Access port initiated error responses are:

AHB-AP reads after an abort

After a DAPABORT operation has been carried out, and an external transfer is still pending, that is, the TrInProg bit is still HIGH, reads of all registers return a normal response except for reads of the Data Read/Write Register and banked registers which cannot initiate a new system read transfer. Reads of the Data Read/Write Register and banked registers return an error response until the TrInProg bit in the Control/Status Word Register is cleared because of the system transfer completing, or because of a reset.

AHB-AP writes after an abort

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

Copyright © 2004-2009 ARM. All rights reserved.ARM DDI 0314H
Non-Confidential