
Debug support (DBG)
RM0351
1794/1830
DocID024597 Rev 5
48.15.4 Configuration
example
To output a simple value to the TPIU:
•
Configure the TPIU and enable the I/IO_TRACEN to assign TRACE I/Os in the
STM32L4x5/STM32L4x6 debug configuration register
•
Write 0xC5ACCE55 to the ETM Lock Access Register to unlock the write access to the
ITM registers
•
Write 0x00001D1E to the control register (configure the trace)
•
Write 0000406F to the Trigger Event register (define the trigger event)
•
Write 0000006F to the Trace Enable Event register (define an event to start/stop)
•
Write 00000001 to the Trace Start/stop register (enable the trace)
•
Write 0000191E to the ETM Control Register (end of configuration)
48.16
MCU debug component (DBGMCU)
The MCU debug component helps the debugger provide support for:
•
Low-power modes
•
Clock control for timers, watchdog, I
2
C and bxCAN during a breakpoint
•
Control of the trace pins assignment
48.16.1 Debug
support
for low-power modes
To enter low-power mode, the instruction WFI or WFE must be executed.
The MCU implements several low-power modes which can either deactivate the CPU clock
or reduce the power of the CPU.
The core does not allow FCLK or HCLK to be turned off during a debug session. As these
are required for the debugger connection, during a debug, they must remain active. The
MCU integrates special means to allow the user to debug software in low-power modes.
For this, the debugger host must first set some debug configuration registers to change the
low-power mode behavior:
•
In Sleep mode, DBG_SLEEP bit of DBGMCU_CR register must be previously set by
the debugger. This will feed HCLK with the same clock that is provided to FCLK
(system clock previously configured by the software).
•
In Stop mode, the bit DBG_STOP must be previously set by the debugger. This will
enable the internal RC oscillator clock to feed FCLK and HCLK in Stop mode.
•
In Standby mode, the bit DBG_STANDBY must be previously set by the debugger. This
will keep the regulators on, and enable the internal RC oscillator clock to feed FCLK
and HCLK in Standby mode. A system reset is generated internally so that exiting from
Standby is identical than fetching from reset.
The DBGMCU_CR register can be written by the debugger under system reset. If the
debugger host does not support these features, it is still possible to write this register by
software.