16.10.2.2 Operation From a Debug Adapter

Debug adapters should access the DSU registers in the external address range [0x100 – 0x1FFF].

If STATUSB.DAL is equal to 0x0, accessing the first 0x100 bytes causes the DSU security filter to return an error to the DAP.

(SAM L11 only): If STATUSB.DAL is equal to 0x1, debug accesses will go through the DSU security filter but will be forced as non-secure, therefore the DSU internal address space will not be accessible and any access in this case is discarded (writes are ignored, reads return 0) and raise STATUSA.PERR.

Table 16-4. DAP transaction authorizations and error response types
DAL Debugger Access Type DAP transaction allowed?
DSU internal address space DSU external address space Other than PPB PPB
0 Secure No (Bus Error) Yes No (Bus Error) No (Bus Error)
0 Non-Secure No (Bus Error) Yes No (Bus Error) No (Bus Error)
1

(SAM L11 only)

Secure No (PERR) Yes Yes (NS,PERR) Yes (ARMv8M)
1

(SAM L11 only)

Non-Secure No (PERR) Yes Yes (NS,PERR) Yes (ARMv8M)
2 Secure Yes Yes Yes Yes
2 Non-Secure No (PERR) Yes Yes Yes

Bus Error: A Bus Error is sent back to the DAP setting its sticky bit error.

PERR: No bus error, STATUSA.PERR rises, writes are discarded, reads always return 0

NS, PERR: Access forced to non-secure, secure violations are reported in STATUSA.PERR.

Note: Refer to the ARM Debug Interface Architecture Specification for details.