DDI0419C_arm_architecture_v6m_reference_manual

ARMv6-M Debug
case DWT_FUNCTION[N].FUNCTION of
when '0000' valid = FALSE; // Comparator disabled
when '0100' valid = FALSE; // See InstructionAddressMatch()
when '0101' valid = read;
when '0110' valid = !read;
when '0111' valid = TRUE;
otherwise UNPREDICTABLE; // Reserved settings
if valid then
mask = ZeroExtend(Ones(UInt(DWT_MASK[N].MASK)), 32);
if !IsZero(DWT_COMP[N] AND mask) then UNPREDICTABLE;
case size
when 1 comp = DWT_COMP[N];
when 2 comp = DWT_COMP[N]:'0';
when 4 comp = DWT_COMP[N]:'00';
match = ((Daddr AND NOT(mask)) == comp);
else
match = FALSE;
return match;
C1.7.2 Program counter sampling support
The DWT Program Counter Sampling Register, DWT_PCSR, is an IMPLEMENTATION DEFINED option in
ARMv6-M. The register is defined so that a debugger can access it without changing the behavior of any
code currently executing on the device. This provides a mechanism for coarse-grained non-intrusive
profiling of code executing on the processor.
The DWT_PCSR is a word-accessible read-only register. Writes to the register are ignored. Byte or
halfword reads are UNPREDICTABLE. When the register is read it returns one of the following:
• the address of an instruction recently executed by the processor
• 0xFFFFFFFF if DWT_PCSR is implemented and any of the following apply:
— the processor is in Debug state
— the processor is in a state and mode where non-invasive debug is not permitted
— the address of a recently-executed instruction is not available.
• RAZ/WI if DWT_PCSR is not implemented.
Note
• There is no architectural definition of recently executed. The delay between an instruction being
executed by the processor and its address appearing in the DWT_PCSR is not defined. There is no
guaranteed relationship between the program counter for a piece of code designed to read the
DWT_PCSR and the value read. The DWT_PCSR is intended only for use by an external agent to
provide statistical information for code profiling. Read accesses made to the DWT_PCSR directly by
the ARM processor can return an UNKNOWN value.
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