User guide

Data Watchpoint and Trace Unit

ID072410 Non-Confidential

8.2 DWT functional description

A full DWT contains four comparators that you can configure as

• a hardware watchpoint

• an ETM trigger

• a PC sampler event trigger

• a data address sampler event trigger.

The first comparator, DWT_COMP0, can also compare against the clock cycle counter,

CYCCNT. You can also use the second comparator, DWT_COMP1, as a data comparator.

A reduced DWT contains one comparator that you can use as a watchpoint or as a trigger. It does

not support data matching.

The DWT if present contains counters for:

• clock cycles (CYCCNT)

• folded instructions

• Load Store Unit (LSU) operations

• sleep cycles

• CPI, that is all instruction cycles except for the first cycle

• interrupt overhead.

Note

An event is generated each time a counter overflows.

You can configure the DWT to generate PC samples at defined intervals, and to generate

interrupt event information.

The DWT provides periodic requests for protocol synchronization to the ITM and the TPIU, if

the your implementation includes the Cortex-M3 TPIU.