See arduino#49.

1. Fix for anomaly in micros() whwn the counter wrapped just before it was read
2. Specify timer configuration as constants to make micros() considerably faster

Author: Kees-van-der-Oord

.gitignore

@@ -3,4 +3,6 @@ cores/arduino/mydebug.cpp
 libraries/Storage/.development
 cores/arduino/mydebug.cpp.donotuse
 .DS_Store
-.DS_Store?
+.DS_Store?
+/.vs
+/.gitignore

cores/arduino/time.cpp

@@ -2,8 +2,10 @@
 #include "IRQManager.h"
 #include "FspTimer.h"
 
+// this file implements the following public funcions: delay, delayMicroseconds, yield, millis, micros
+// The millis and micros implementation uses timer AGT0 (24 HMz, 16-bits, count-down mode, 1 ms period)
+
 volatile unsigned long agt_time_ms = 0;
-uint32_t _freq_hz = 0;
 
 __attribute__((weak)) void delay(uint32_t ms) {
 	R_BSP_SoftwareDelay(ms, BSP_DELAY_UNITS_MILLISECONDS);
@@ -17,20 +19,24 @@ __attribute__((weak)) void yield() {
 }
 
 static FspTimer main_timer;
-
-static uint32_t _top_counter;
+// specifying these details as constants makes micros() faster !
+#define _timer_type           AGT_TIMER
+#define _timer_index          0
+#define _timer_underflow_bit  R_AGT0->AGTCR_b.TUNDF
+#define _timer_clock_divider  TIMER_SOURCE_DIV_8 // dividers 1, 2, 4 and 8 work because _timer_period is < 16-bit. bug in R4 1.0.2: divider 4 acts as 1 !? 
+#define _timer_clock_freq     24000000UL
+#define _timer_ticks_per_us   (_timer_clock_freq / ((1 << _timer_clock_divider) * 1000000UL))
+#define _timer_period         (_timer_ticks_per_us * 1000UL)
 
 static void timer_micros_callback(timer_callback_args_t __attribute((unused)) *p_args) {
-	agt_time_ms += 1; //1ms
+	agt_time_ms += 1;
 }
 
 void startAgt() {
-	main_timer.begin(TIMER_MODE_PERIODIC, AGT_TIMER, 0, 2000.0f, 0.5f, timer_micros_callback);
-	IRQManager::getInstance().addPeripheral(IRQ_AGT,(void*)main_timer.get_cfg());
+	main_timer.begin(TIMER_MODE_PERIODIC, _timer_type, _timer_index, _timer_period, 1, _timer_clock_divider, timer_micros_callback);;
+	main_timer.setup_overflow_irq();
 	main_timer.open();
-	_top_counter = main_timer.get_counter();
-	main_timer.start();
-	_freq_hz = main_timer.get_freq_hz();
+	main_timer.start(); // bug in R4 1.0.2: calling start() is not necessary: open() starts the counter already !?
 }
 
 unsigned long millis()
@@ -43,10 +49,11 @@ unsigned long millis()
 }
 
 unsigned long micros() {
-
-	// Convert time to us
+	// Return time in us
 	NVIC_DisableIRQ(main_timer.get_cfg()->cycle_end_irq);
-	uint32_t time_us = ((main_timer.get_period_raw() - main_timer.get_counter()) * 1000 / main_timer.get_period_raw()) +  (agt_time_ms * 1000);
+	uint32_t ms = agt_time_ms;
+	uint32_t cnt = main_timer.get_counter();
+	if (_timer_underflow_bit && (cnt > (_timer_period / 2))) ++ms; // the counter wrapped arround just before it was read
 	NVIC_EnableIRQ(main_timer.get_cfg()->cycle_end_irq);
-	return time_us;
+	return  ms * 1000 + (((_timer_period - 1) - cnt) / _timer_ticks_per_us);
 }