swo-init.c

/*
 * The following is from
 *     https://community.st.com/s/question/0D53W00000IWs2g/how-to-enable-swo-with-stlink-utility-on-stm32f407gdisc1
 * But there are other implementations that are virtually identical
 *     https://mcuoneclipse.com/2016/10/17/tutorial-using-single-wire-output-swo-with-arm-cortex-m-and-eclipse/#more-19719
 */
//-------------------------------------------------------------------------------------------------
/*
	Initialize the SWO trace port for debug message printing
	portMask : Stimulus bit mask to be configured
	cpuCoreFreqHz : CPU core clock frequency in Hz
	baudrate : SWO frequency in Hz
*/
 
void swoInit (uint32_t portMask, uint32_t cpuCoreFreqHz, uint32_t baudrate)
{
	uint32_t SWOPrescaler = (cpuCoreFreqHz / baudrate) - 1u ; // baudrate in Hz, note that cpuCoreFreqHz is expected to match the CPU core clock
 
	CoreDebug->DEMCR = CoreDebug_DEMCR_TRCENA_Msk; 		// Debug Exception and Monitor Control Register (DEMCR): enable trace in core debug
    // Uncomment following for ST devices
	// DBGMCU->CR	= 0x00000027u ;							// DBGMCU_CR : TRACE_IOEN DBG_STANDBY DBG_STOP 	DBG_SLEEP
	TPI->SPPR	= 0x00000002u ;							// Selected PIN Protocol Register: Select which protocol to use for trace output (2: SWO)
	TPI->ACPR	= SWOPrescaler ;						// Async Clock Prescaler Register: Scale the baud rate of the asynchronous output
	ITM->LAR	= 0xC5ACCE55u ;							// ITM Lock Access Register: C5ACCE55 enables more write access to Control Register 0xE00 :: 0xFFC
	ITM->TCR	= 0x0001000Du ;							// ITM Trace Control Register
	ITM->TPR	= ITM_TPR_PRIVMASK_Msk ;				// ITM Trace Privilege Register: All stimulus ports
	ITM->TER	= portMask ;							// ITM Trace Enable Register: Enabled tracing on stimulus ports. One bit per stimulus port.
	DWT->CTRL	= 0x400003FEu ;							// Data Watchpoint and Trace Register
	TPI->FFCR	= 0x00000100u ;							// Formatter and Flush Control Register
 
	// ITM/SWO works only if enabled from debugger.
	// If ITM stimulus 0 is not free, don't try to send data to SWO
	if (ITM->PORT [0].u8 == 1)
	{
		bItmAvailable = 1 ;
	}
}