Add example to demo sub-ms interval

Add Argument_None_uS example to demonstrate how to use sub-ms interval

examples/Argument_None_uS/Argument_None_uS.ino

@@ -0,0 +1,181 @@
+/****************************************************************************************************************************
+  Argument_None_uS.ino
+  For SAMD boards
+  Written by Khoi Hoang
+  
+  Built by Khoi Hoang https://github.com/khoih-prog/SAMD_TimerInterrupt
+  Licensed under MIT license
+  
+  Now even you use all these new 16 ISR-based timers,with their maximum interval practically unlimited (limited only by
+  unsigned long miliseconds), you just consume only one SAMD timer and avoid conflicting with other cores' tasks.
+  The accuracy is nearly perfect compared to software timers. The most important feature is they're ISR-based timers
+  Therefore, their executions are not blocked by bad-behaving functions / tasks.
+  This important feature is absolutely necessary for mission-critical tasks.
+  
+  Based on SimpleTimer - A timer library for Arduino.
+  Author: mromani@ottotecnica.com
+  Copyright (c) 2010 OTTOTECNICA Italy
+  
+  Based on BlynkTimer.h
+  Author: Volodymyr Shymanskyy
+  
+  Version: 1.3.0
+
+  Version Modified By   Date      Comments
+  ------- -----------  ---------- -----------
+  1.0.0   K Hoang      30/10/2020 Initial coding
+  1.0.1   K Hoang      06/11/2020 Add complicated example ISR_16_Timers_Array using all 16 independent ISR Timers.
+  1.1.1   K.Hoang      06/12/2020 Add Change_Interval example. Bump up version to sync with other TimerInterrupt Libraries
+  1.2.0   K.Hoang      08/01/2021 Add better debug feature. Optimize code and examples to reduce RAM usage
+  1.3.0   K.Hoang      02/04/2021 Add support to Sparkfun SAMD21 and SAMD51 boards
+*****************************************************************************************************************************/
+
+/*
+   Notes:
+   Special design is necessary to share data between interrupt code and the rest of your program.
+   Variables usually need to be "volatile" types. Volatile tells the compiler to avoid optimizations that assume
+   variable can not spontaneously change. Because your function may change variables while your program is using them,
+   the compiler needs this hint. But volatile alone is often not enough.
+   When accessing shared variables, usually interrupts must be disabled. Even with volatile,
+   if the interrupt changes a multi-byte variable between a sequence of instructions, it can be read incorrectly.
+   If your data is multiple variables, such as an array and a count, usually interrupts need to be disabled
+   or the entire sequence of your code which accesses the data.
+*/
+
+#if !( defined(ARDUINO_SAMD_ZERO) || defined(ARDUINO_SAMD_MKR1000) || defined(ARDUINO_SAMD_MKRWIFI1010) \
+    || defined(ARDUINO_SAMD_NANO_33_IOT) || defined(ARDUINO_SAMD_MKRFox1200) || defined(ARDUINO_SAMD_MKRWAN1300) || defined(ARDUINO_SAMD_MKRWAN1310) \
+    || defined(ARDUINO_SAMD_MKRGSM1400) || defined(ARDUINO_SAMD_MKRNB1500) || defined(ARDUINO_SAMD_MKRVIDOR4000) || defined(__SAMD21G18A__) \
+    || defined(ARDUINO_SAMD_CIRCUITPLAYGROUND_EXPRESS) || defined(__SAMD21E18A__) || defined(__SAMD51__) || defined(__SAMD51J20A__) || defined(__SAMD51J19A__) \
+    || defined(__SAMD51G19A__) || defined(__SAMD51P19A__) || defined(__SAMD21G18A__) )
+  #error This code is designed to run on SAMD21/SAMD51 platform! Please check your Tools->Board setting.
+#endif
+
+// These define's must be placed at the beginning before #include "SAMDTimerInterrupt.h"
+// _TIMERINTERRUPT_LOGLEVEL_ from 0 to 4
+// Don't define _TIMERINTERRUPT_LOGLEVEL_ > 0. Only for special ISR debugging only. Can hang the system.
+// Don't define TIMER_INTERRUPT_DEBUG > 2. Only for special ISR debugging only. Can hang the system.
+#define TIMER_INTERRUPT_DEBUG         0
+#define _TIMERINTERRUPT_LOGLEVEL_     0
+
+#include "SAMDTimerInterrupt.h"
+
+//#ifndef LED_BUILTIN
+//  #define LED_BUILTIN       13
+//#endif
+
+#ifndef LED_BLUE
+  #define LED_BLUE          2
+#endif
+
+#ifndef LED_RED
+  #define LED_RED           8
+#endif
+
+#define TIMER0_INTERVAL_MS        500   //1000
+#define TIMER0_INTERVAL_US        200   //1000
+
+volatile uint32_t preMillisTimer0 = 0;
+
+// Depending on the board, you can select SAMD21 Hardware Timer from TC3-TCC
+// SAMD21 Hardware Timer from TC3 or TCC
+// SAMD51 Hardware Timer only TC3
+
+// Init SAMD timer TIMER_TC3
+SAMDTimer ITimer0(TIMER_TC3);
+
+void TimerHandler0()
+{
+  static bool toggle0 = false;
+
+#if (TIMER_INTERRUPT_DEBUG > 0)
+    static uint32_t curMillis = 0;
+
+    curMillis = millis();
+
+    if (curMillis > TIMER0_INTERVAL_MS)
+    {
+      Serial.print(F("ITimer0: millis() = ")); Serial.print(curMillis);
+      Serial.print(F(", delta = ")); Serial.println(curMillis - preMillisTimer0);
+    }
+
+    preMillisTimer0 = curMillis;
+#endif 
+
+  //timer interrupt toggles pin LED_BUILTIN
+  digitalWrite(LED_BUILTIN, toggle0);
+  toggle0 = !toggle0;
+}
+
+#if (TIMER_INTERRUPT_USING_SAMD21)
+
+#define TIMER1_INTERVAL_MS        2000
+
+volatile uint32_t preMillisTimer1 = 0;
+
+// Init SAMD timer TIMER_TCC
+SAMDTimer ITimer1(TIMER_TCC);
+
+void TimerHandler1()
+{
+  static bool toggle1 = false;
+
+  #if (TIMER_INTERRUPT_DEBUG > 0)
+    static uint32_t curMillis = 0;
+
+    curMillis = millis();
+
+    if (curMillis > TIMER1_INTERVAL_MS)
+    {
+      Serial.print(F("ITimer1: millis() = ")); Serial.print(curMillis);
+      Serial.print(F(", delta = ")); Serial.println(curMillis - preMillisTimer1);
+    }
+
+    preMillisTimer0 = curMillis;
+#endif
+
+  //timer interrupt toggles outputPin
+  digitalWrite(LED_BLUE, toggle1);
+  toggle1 = !toggle1;
+}
+#endif
+
+void setup()
+{
+  pinMode(LED_BUILTIN, OUTPUT);
+  pinMode(LED_BLUE, OUTPUT);
+
+  Serial.begin(115200);
+  while (!Serial);
+
+  delay(100);
+
+  Serial.print(F("\nStarting Argument_None_uS on ")); Serial.println(BOARD_NAME);
+  Serial.println(SAMD_TIMER_INTERRUPT_VERSION);
+  Serial.print(F("CPU Frequency = ")); Serial.print(F_CPU / 1000000); Serial.println(F(" MHz"));
+
+  // Interval in microsecs
+  //if (ITimer0.attachInterruptInterval(TIMER0_INTERVAL_MS * 1000, TimerHandler0))
+  if (ITimer0.attachInterruptInterval(TIMER0_INTERVAL_US, TimerHandler0))
+  {
+    preMillisTimer0 = millis();
+    Serial.print(F("Starting  ITimer0 OK, millis() = ")); Serial.println(preMillisTimer0);
+  }
+  else
+    Serial.println(F("Can't set ITimer0. Select another freq. or timer"));
+
+#if (TIMER_INTERRUPT_USING_SAMD21)
+  // Interval in microsecs
+  if (ITimer1.attachInterruptInterval(TIMER1_INTERVAL_MS * 1000, TimerHandler1))
+  {
+    preMillisTimer1 = millis();
+    Serial.print(F("Starting ITimer1 OK, millis() = ")); Serial.println(preMillisTimer1);
+  }
+  else
+    Serial.println(F("Can't set ITimer1. Select another freq. or timer"));
+#endif
+}
+
+void loop()
+{
+
+}