Implement function to get date in microseconds

This function is executed in critical section, i.e. it can't be interrupted by interruptions.

prog/sources/time.cpp

@@ -6,6 +6,26 @@ static void startSystick (BOOT_MODE) {
 	SYST_RVR = CPU_MHZ * 1000 - 1 ; // Underflow every ms
 	SYST_CVR = 0 ;
 	SYST_CSR = SYST_CSR_CLKSOURCE | SYST_CSR_ENABLE ;
+
+	// Configure and chain PIT0 and PIT1 for 64-bit counting
+
+	// Power on PIT
+	SIM_SCGC6 |= SIM_SCGC6_PIT ;
+
+	// Enable PIT module
+	PIT_MCR = 0 ;
+
+	// Disable PIT0 and PIT1
+	PIT_TCTRL (0) = 0 ;
+	PIT_TCTRL (1) = 0 ;
+
+	// PIT0 and PIT1 down-count: initialize them with all 1's
+	PIT_LDVAL (0) = UINT32_MAX ;
+	PIT_LDVAL (1) = UINT32_MAX ;
+
+	// Enable PIT0 and PIT1: start counting, chain PI1 to PIT0, no interrupt
+	PIT_TCTRL (1) = PIT_TCTRL_CHN | PIT_TCTRL_TEN ;
+	PIT_TCTRL (0) = PIT_TCTRL_TEN ;
 }
 
 MACRO_BOOT_ROUTINE (startSystick);
@@ -49,6 +69,22 @@ uint32_t millis(ANY_MODE) {
 	return gUptime;
 }
 
+uint64_t section_micros(SECTION_MODE) {
+
+	// To obtain the correct value, first read LTMR64H and then LTMR64L
+	uint64_t result = PIT_LTMR64H ;
+	result <<= 32 ;
+	result |= PIT_LTMR64L ;
+
+	// PIT0 and PIT1 actually downcount
+	result = ~ result ;
+
+	// Divide by the clock frequency in MHz for getting microsecond count
+	result /= busMHZ () ;
+
+	return result;
+}
+
 uint32_t systick(ANY_MODE) {
 	return SYST_CVR;
 }

prog/sources/time.h

@@ -15,6 +15,13 @@ void systickInterruptServiceRoutine (SECTION_MODE) asm ("interrupt.section.SysTi
 
 uint32_t millis(ANY_MODE);
 
+//$section fonction.micros
+
+uint64_t micros (USER_MODE) asm ("fonction.micros") ;
+
+uint64_t section_micros (SECTION_MODE) asm ("section.fonction.micros") ;
+
+
 uint32_t systick(ANY_MODE);
 
 #define MACRO_REAL_TIME_ISR(ROUTINE) \