Table of Contents
Advertisement
ARM DDI 0337B
•
The AP access does not complete until the AP signals it as completed. For
example, if you access a Memory Access Port (AHB-AP), the access might cause
an access to a memory system connected to the AHB-AP. In this case, the access
does not complete until the memory system signals to the AHB-AP that the
memory access has completed.
The WAIT response to a DPACC or APACC access
A WAIT response indicates that the previous transaction has not completed. The host
should retry the DPACC or APACC access.
Note
The previous transaction might be either a DP or an AP access. Accesses to the DP are
stalled, by returning WAIT, until any previous AP transaction has completed.
Normally, if software detects a WAIT response, it retries the same transfer. This enables
the protocol to process data as quickly as possible. However, if the software has retried
a transfer a number of times, allowing enough time for a slow interconnect and memory
system to respond, it might write to the ABORT register, to cancel the operation. This
signals to the active AP that it should terminate the transfer it is currently attempting,
and permits access to other parts of the debug system. An AP might not be able to
terminate a transfer on its ASIC interface. However, on receiving an ABORT, the AP
should free its JTAG interface.
Update-DR operation following a WAIT response
No request is generated at the Update-DR state, and the shifted-in data is discarded. The
captured value of ReadResult[31:0] is Unpredictable.
Note
You can detect a WAIT response without shifting through the entire DP or AP Access
Register, see the response details in Table 12-4 on page 12-12.
Sticky overrun behavior on DPACC and APACC accesses
At the Capture-DR state, if the previous transaction has not completed a WAIT response
is generated. When this happens, if the Overrun Detect flag is set, the Sticky Overrun
flag, STICKYORUN, is set. See The Control/Status Register, CTRL/STAT on
page 12-53 for more information about the Overrun Detect and Sticky Overrun flags.
While the previous transaction remains not completed, subsequent scans also receive a
WAIT response.
Copyright © 2005, 2006 ARM Limited. All rights reserved.
Debug Port
12-15
Advertisement
Table of Contents
