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en:examples:timer:delay [2015/11/03 06:04] – raivo.sellen:examples:timer:delay [2020/07/20 09:00] (current) – external edit 127.0.0.1
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-~~PB~~+<pagebreak>
 ====== Delay ====== ====== Delay ======
  
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 <code c> <code c>
-// +// Software delay in milliseconds
-// Software delay in milliseconds. +
-//+
 void sw_delay_ms(unsigned short count) void sw_delay_ms(unsigned short count)
 { {
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  while (count-- > 0)  while (count-- > 0)
  {  {
- // 1ms delay with a special function.+ // 1ms delay with a special function
  _delay_ms(1);  _delay_ms(1);
  }  }
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 <code c> <code c>
-// +// The demonstration program of the software delay of the HomeLab 
-// The demonstration program of the software delay of the HomeLab. +// The program is blinking a LED for a moment after ~1 second
-// The program is blinking a LED for a moment after ~1 second. +
-//+
 #include <homelab/pin.h> #include <homelab/pin.h>
 #include <homelab/delay.h> #include <homelab/delay.h>
    
-// 
-// Determining the pin of the test LED 
-// 
-pin debug_led = PIN(B, 7); 
-  
-// 
 // Main program // Main program
-// 
 int main(void) int main(void)
 { {
- // Setting the pin of the LED as output. + // Setting the pin of the LED as output 
- pin_setup_output(debug_led);+ pin_setup_output(led_debug);
    
  // Endless loop   // Endless loop
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  {  {
  // Lighting the LED  // Lighting the LED
- pin_clear(debug_led);+ pin_clear(led_debug);
    
  // Software delay for 100 ms  // Software delay for 100 ms
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  // Switching off the LED  // Switching off the LED
- pin_set(debug_led);+ pin_set(led_debug);
  
- // Software delay for 900 milliseconds.+ // Software delay for 900 milliseconds
  sw_delay_ms(900);  sw_delay_ms(900);
  }  }
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 Although it seems that the LED blinks in every 1 second, the time is actually a little bit longer, because the callouts of LED’s and delay functions are taking a couple of clock rates of the microcontroller Although it seems that the LED blinks in every 1 second, the time is actually a little bit longer, because the callouts of LED’s and delay functions are taking a couple of clock rates of the microcontroller
  
-The program code below is a delay function based on a timer, which is simplified a little bit. The principle of counting is the same as it is at software delay function – a desired amount of 1 ms long delays are produced. The delay is produced with an 8-bit ATmega 128 counter 0. It is calculated previously that at clock frequency 14,7456 Mhz the timing signal has to be divided at least 64 times, so that the counter would not reach to overflow in 1 ms. The value which the counter must have so that the overflow occurs after 1 ms is presented in the form of an expression and the variable is //timer_start//. //F_CPU// which is a constant in macro-language, that shows clock frequency in Hz. The clock frequency should be 25,6 at the moment but since fractions can not be used, the initial value will be set 26. Unfortunately here arises a mistake in delay time, however it is fairly small (-1,7 μs). +The program code below is a delay function based on a timer, which is simplified a little bit. The principle of counting is the same as it is at software delay function – a desired amount of 1 ms long delays are produced. The delay is produced with an 8-bit counter 0. It is calculated previously that at clock frequency 14,7456 Mhz the timing signal has to be divided at least 64 times, so that the counter would not reach to overflow in 1 ms. The value which the counter must have so that the overflow occurs after 1 ms is presented in the form of an expression and the variable is //timer_start//. //F_CPU// which is a constant in macro-language, that shows clock frequency in Hz. The clock frequency should be 25,6 at the moment but since fractions can not be used, the initial value will be set 26. Unfortunately here arises a mistake in delay time, however it is fairly small (-1,7 μs). 
  
 In the cycle takes place initialing of the counter and zeroing the flag of the overflow (by writing 1 into that). Then is waited until the counter counts to 256 from the initial value, i.e. to the overflow. At the moment of the overflow the flag goes high and the delay of 1 ms has taken place. In the end of the function the timer is stopped.        In the cycle takes place initialing of the counter and zeroing the flag of the overflow (by writing 1 into that). Then is waited until the counter counts to 256 from the initial value, i.e. to the overflow. At the moment of the overflow the flag goes high and the delay of 1 ms has taken place. In the end of the function the timer is stopped.       
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 <code c> <code c>
-// +// Hardware delay in milliseconds
-// Hardware delay in milliseconds. +
-//+
 void hw_delay_ms(unsigned short count) void hw_delay_ms(unsigned short count)
 {  {
- // Calculating the initial value of the timer.+ // Calculating the initial value of the timer
  register unsigned char timer_start = 256 - F_CPU / 1000 / 64;  register unsigned char timer_start = 256 - F_CPU / 1000 / 64;
   
- // Starting the timer.+ // Starting the timer
  timer0_init_normal(TIMER0_PRESCALE_64);  timer0_init_normal(TIMER0_PRESCALE_64);
  
- // Counting the variable of the delay to the 0.+ // Counting the variable of the delay to the 0
  while (count-- > 0)  while (count-- > 0)
  {  {
- // Initializing the timer.+ // Initializing the timer
  timer0_set_value(timer_start);  timer0_set_value(timer_start);
  
- // Zeroing the overflow flag.+ // Zeroing the overflow flag
  timer0_overflow_flag_clear();   timer0_overflow_flag_clear();
   
- // Waiting for overflow.+ // Waiting for overflow
  while (!timer0_overflow_flag_is_set())  while (!timer0_overflow_flag_is_set())
  {  {
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  }  }
  
- // Zeroing the overflow flag.+ // Zeroing the overflow flag
  timer0_overflow_flag_clear();   timer0_overflow_flag_clear();
  
- // Stoping the timer.+ // Stoping the timer
  timer0_stop();   timer0_stop();
 +}
 +</code>
 +
 +Referenced delay function uses a timer library whose source code for ATmega controller looks like the following:
 +
 +<code c>
 +// Timer 0 prescaler selection type
 +typedef enum
 +{
 + TIMER0_NO_PRESCALE         = 0x01,
 + TIMER0_PRESCALE_8          = 0x02,
 + TIMER0_PRESCALE_32         = 0x03,
 + TIMER0_PRESCALE_64         = 0x04,
 + TIMER0_PRESCALE_128        = 0x05,
 + TIMER0_PRESCALE_256        = 0x06,
 + TIMER0_PRESCALE_1024       = 0x07
 +}
 +timer0_prescale;
 +
 +// Setting Timer 0 to a normal mode
 +inline void timer0_init_normal(timer0_prescale prescale)
 +{
 + TCCR0 = prescale & 0x07;
 +}
 + 
 +// Stopping the Taimer 0
 +inline void timer0_stop()
 +{
 + TCCR0 = 0x00;
 +}
 +
 +// Taimer 0 value set
 +inline void timer0_set_value(unsigned char value)
 +{
 + TCNT0 = value;
 +}
 +
 +// Timer 0 overflow flag clear
 +inline void timer0_overflow_flag_clear(void)
 +{
 + bit_set(TIFR, TOV0);
 +}
 +
 +// Timer 0 overflow flag state reading
 +inline bool timer0_overflow_flag_is_set(void)
 +{
 + return (bit_is_set(TIFR, TOV0) ? true : false);
 } }
 </code> </code>
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 <code c> <code c>
-// +// Demonstration program of hardware delay of the HomeLab 
-// Demonstration program of hardware delay of the HomeLab. +// The Program blinks LED for a moment after every ~1 second
-// The Program blinks LED for a moment after every ~1 second. +
-//+
 #include <homelab/pin.h> #include <homelab/pin.h>
 #include <homelab/delay.h> #include <homelab/delay.h>
  
-// Main program.+// Main program
 int main(void) int main(void)
 { {
- // Setting the pin of the  LED as output. + // Setting the pin of the  LED as output 
- pin_setup_output(debug_led);+ pin_setup_output(led_debug);
  
- // Endless loop. + // Endless loop
  while (true)  while (true)
  {  {
- // Lighting the LED. + // Lighting the LED 
- pin_clear(debug_led);+ pin_clear(led_debug);
   
- // Hardware delay for 100 milliseconds.+ // Hardware delay for 100 milliseconds
  hw_delay_ms(100);  hw_delay_ms(100);
  
- // Switch off of the LED. + // Switch off of the LED 
- pin_set(debug_led);+ pin_set(led_debug);
   
- // Hardware delay for 900 milliseconds.+ // Hardware delay for 900 milliseconds
  hw_delay_ms(900);  hw_delay_ms(900);
  }  }
en/examples/timer/delay.1446530655.txt.gz · Last modified: 2020/07/20 09:00 (external edit)
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