6.3.6 Debugger Reads of Actionable Registers
Some peripheral registers cause particular actions when read, e.g FIFOs which pop and IFC registers which clear the IF flags when
read. This can cause problems when debugging and the user wants to read the value without triggering the read action. For this rea-
son, by default, the peripherals will not execute these triggered actions when an attached debugger is performing the read accesses
through the AAP. To override this behavior, the debugger can configure the MASTERTYPE bitfield of the Cortex-M4 AHB Access Port
CSW register in order to emulate a core access when performing system bus transfers.
Note:
Registers with actionable reads are noted in their register descriptions. Refer to
Table 1.1 Register Access Types on page 26
Note:
The following peripherals do not respect the debugger master override, and so may still cause their triggered actions to occur
(e.g., when reading IFC):
6.3.7 Debug Recovery
Debug recovery is the ability to stall the system bus before the Cortex-M4 executes code. For example, the first few instructions may
disconnect the debugger pins. When this occurs it is difficult to connect the debugger and halt the Cortex-M4 before the Cortex-M4
starts to execute. By holding down pin reset, issuing the System Bus Stall AAP instruction, then releasing pin reset, the debugger can
stall the system bus before the Cortex-M4 has a chance to execute. Because the system is under reset during this procedure the De-
bugger can not look for ACK's from the part. Once the system bus is stalled, the FLASH can be erased by issuing the AAP_CMDKEY
and then the writting the DEVICEERASE in the AAP_CMD register.
6.4 Register Map
The offset register address is relative to the registers base address.
Offset
Name
Type
Description
W1
W1
R
RW
W1
R
RW
R
R
Reference Manual
DBG - Debug Interface
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