Data Watchpoint & Trace Unit

Use DWT to perform PC sampling and trace memory accesses. More...

Classes
struct	DWTOptions
	DWT configuration. More...

Enumerations
enum	DWTSyncTap { DWTSyncTapDisabled = 0 , DWTSyncTap24 = 1 , DWTSyncTap26 = 2 , DWTSyncTap28 = 3 }
	Interval of ITM synchronization packet. More...
enum	DWTCycleTap { DWTCycleTap6 = 0 , DWTCycleTap10 = 1 }
	Interval of PC sampling and event counter packets. More...

Functions
static void	DWTSetup (const DWTOptions *options)
	Configures DWT component. More...
static void	DWTEnableComparator (uint8_t comparator, uintptr_t address, uint8_t ignoreBits, bool emitRange, uint8_t function)
	Configures DWT comparator. More...
static void	DWTDisableComparator (uint8_t comparator)
	Disables DWT comparator. More...

Detailed Description

Use DWT to perform PC sampling and trace memory accesses.

Data Watchpoint & Trace unit provides built-in capabilites for:

• PC sampling with configurable interval
• Exception entry/exit trace
• Events counters
• Watchpoints allowing to output trace packet when memory region is accessed
• Cycle counter

DWT outputs data to ITM which forwards it to formatter. When configuring ITM option ITMOptions::ForwardDWT must be enabled.

Relationships between DWT clocks and packets

Reference: ARMv7-M Architecture Reference Manual, chapter C1.8 The Data Watchpoint and Trace unit

Enumeration Type Documentation

DWTSyncTap

enum DWTSyncTap

Interval of ITM synchronization packet.

See ARMv7-M Architecture Reference Manual, section C1.8.3 "CYCCNT cycle counter and related timers" for details

Enumerator
DWTSyncTapDisabled	Disabled.
DWTSyncTap24	Output synchronization when CYCCNT[24] bit changes. \(PacketRate = \frac{ProcessorClock}{16 \cdot 10^6{}}\)
DWTSyncTap26	Output synchronization when CYCCNT[26] bit changes. \(PacketRate = \frac{ProcessorClock}{64 \cdot 10^6{}}\)
DWTSyncTap28	Output synchronization when CYCCNT[28] bit changes. \(PacketRate = \frac{ProcessorClock}{16 \cdot 256^6{}}\)

DWTCycleTap

enum DWTCycleTap

Interval of PC sampling and event counter packets.

See ARMv7-M Architecture Reference Manual, section C1.8.3 "CYCCNT cycle counter and related timers" for details

Enumerator
DWTCycleTap6	Output packet when bit CYCCNT[6] changes. \(POSTCNTClockRate = \frac{ProcessorClock}{64}\)
DWTCycleTap10	Output packet when bit CYCCNT[10] changes. \(POSTCNTClockRate = \frac{ProcessorClock}{1024}\)

Function Documentation

DWTSetup()

void DWTSetup ( const DWTOptions *  options )

inlinestatic

Configures DWT component.

Note that there is no validation if specified configuration is valid (e.g. sampling prescaler values) and there are no checks to verify MCU capabilities (enabling exception tracing when it is not implemented).

Parameters

options

DWT configuration

DWTEnableComparator()

void DWTEnableComparator ( uint8_t  comparator, uintptr_t  address, uint8_t  ignoreBits, bool  emitRange, uint8_t  function  )

inlinestatic

Configures DWT comparator.

Comparator might issue a trace packet when specified memory range is accesses for read or write.

Number of comparators is vendor-specific, check with documention how many are available. This function does not check if specified comparator is available.

Comparator can monitor single byte in memory or range by ignoring specified number of least significant bits, e.g. to monitor single uint32_t variable setup address parameter to variable address and ignoreBits parameter to 2

Parameters

comparator	Comparator to use
address	Watchpoint base address
ignoreBits	Number of bits to ignore
emitRange	If true, DWT will emit packet with actual data access address. if false - packet with program counter that resulted in memory access.
function	Comparator function, see ARMv7-M Architecture Reference Manual, table C1-14 for list of available functions

DWTDisableComparator()

void DWTDisableComparator ( uint8_t  comparator )

inlinestatic

Disables DWT comparator.

Number of comparators is vendor-specific, check with documention how many are available. This function does not check if specified comparator is available.

Parameters

comparator

Comparator to disable