RM0367 Rev 7 961/1043
RM0367 Debug support (DBG)
970
33.5.4 DP and AP read/write accesses
• Read accesses to the DP are not posted: the target response can be immediate (if
ACK=OK) or can be delayed (if ACK=WAIT).
• Read accesses to the AP are posted. This means that the result of the access is
returned on the next transfer. If the next access to be done is NOT an AP access, then
the DP-RDBUFF register must be read to obtain the result.
The READOK flag of the DP-CTRL/STAT register is updated on every AP read access
or RDBUFF read request to know if the AP read access was successful.
• The SW-DP implements a write buffer (for both DP or AP writes), that enables it to
accept a write operation even when other transactions are still outstanding. If the write
buffer is full, the target acknowledge response is “WAIT”. With the exception of
IDCODE read or CTRL/STAT read or ABORT write which are accepted even if the write
buffer is full.
• Because of the asynchronous clock domains SWCLK and HCLK, two extra SWCLK
cycles are needed after a write transaction (after the parity bit) to make the write
effective internally. These cycles should be applied while driving the line low (IDLE
state)
This is particularly important when writing the CTRL/STAT for a power-up request. If the
next transaction (requiring a power-up) occurs immediately, it will fail.
33.5.5 SW-DP registers
Access to these registers are initiated when APnDP=0
Table 177. SW-DP registers
A[3:2] R/W
CTRLSEL bit
of SELECT
register
Register Notes
00 Read IDCODE
The manufacturer code is set to the default
Arm
®
code for Cortex
®
-M0+:
0x0BC11477 (identifies the SW-DP)
00 Write ABORT
01 Read/Write 0 DP-CTRL/STAT
Purpose is to:
– request a system or debug power-up
– configure the transfer operation for AP
accesses
– control the pushed compare and pushed
verify operations.
– read some status flags (overrun, power-up
acknowledges)
01 Read/Write 1
WIRE
CONTROL
Purpose is to configure the physical serial
port protocol (like the duration of the
turnaround time)
10 Read
READ
RESEND
Enables recovery of the read data from a
corrupted debugger transfer, without
repeating the original AP transfer.
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