9.2  SAMD21 : Entrées/sorties

• Plusieurs banques (bank) d’E/S numériques.
• Gestion des entrées-sorties numériques avec arm-gcc :

  // Blink code for Adafruit Playground Express (APE)
  // APE chip is an samd21g18a
  // APE LED is on PA17
   
  #include <stdint.h>
  
  // Some constants about PORT A
  #define PORT_BASE 0x41004400
  #define PORT_OFFSET(o) (*(volatile uint32_t *)(PORT_BASE+o))
  
  #define PORTA_DIRSET PORT_OFFSET(0x08)
  #define PORTA_OUTCLR PORT_OFFSET(0x14)
  #define PORTA_OUTSET PORT_OFFSET(0x18)
  
  // Some constants for the LED 
  #define LED_PIN 17
  
  // Some constants for sleep function
  #define STEPS_PER_CHUNK 10000
  
  void my_sleep(unsigned int chunks){
    unsigned int i,s;
    for(s=0;s<chunks;s++){
      for(i=0;i<STEPS_PER_CHUNK;i++){
         // skip CPU cycle or any other statement(s) for making loop 
         // untouched by C compiler code optimizations
         asm volatile ("nop");
      }
    }
  }
  
  // Initialisation of PORT A
  void init_ports(void){
    PORTA_DIRSET=(1<<LED_PIN);   // no need for read/modify/write
    PORTA_OUTCLR=(1<<LED_PIN);  // idem
  }
  
  // Main function
  int main(void) {
    // Initialize ports
    init_ports();
    // Forever loop
    while(1){
      // Fire up LED
      PORTA_OUTSET=(1<<LED_PIN); // no need for read/modify/write
      // Wait for some time
      my_sleep(10);
      // Shut LED
      PORTA_OUTCLR=(1<<LED_PIN); // no need for read/modify/write
      // Wait again for some time
      my_sleep(10);
    }
    return 0;
  }