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  1. /*
  2.    Precise Delay Functions
  3.    V 0.5, Martin Thomas, 9/2004
  4.    
  5.    Inspired by the avr-libc's loop-code
  6. */
  7.  
  8. #ifndef _delay_h_
  9. #define _delay_h_
  10.  
  11. #include <inttypes.h>
  12. #include <avr/io.h>
  13.  
  14. /* delay function for microsec
  15.    4 cpu cycles per loop + 1 cycles(?) overhead
  16.    when a constant is passed. */
  17. static inline void delayloop16(uint16_t count)
  18. {
  19.     asm volatile (  "cp  %A0,__zero_reg__ \n\t"  \
  20.                      "cpc %B0,__zero_reg__ \n\t"  \
  21.                      "breq L_Exit_%=       \n\t"  \
  22.                      "L_LOOP_%=:           \n\t"  \
  23.                      "sbiw %0,1            \n\t"  \
  24.                      "brne L_LOOP_%=       \n\t"  \
  25.                      "L_Exit_%=:           \n\t"  \
  26.                      : "=w" (count)
  27.                      : "0"  (count)
  28.                    );                            
  29. }
  30. // delayloop16(x) eats 4 cycles per x
  31. #define DELAY_US_CONV(us) ((uint16_t)(((((us)*1000L)/(1000000000/F_OSC))-1)/4))
  32. #define delay_us(us)      delayloop16(DELAY_US_CONV(us))
  33.  
  34. /* delay function for millisec
  35.   (6 cycles per x + 20(?) overhead) */
  36. void delayloop32( uint32_t l); // not inline
  37. #define DELAY_MS_CONV(ms) ( (uint32_t) (ms*(F_OSC/6000L)) )
  38. #define delay_ms(ms)  delayloop32(DELAY_MS_CONV(ms))
  39.  
  40. /* mth 9/04:
  41.    Remark uSeconds:
  42.    Main Oscillator Clock given by F_OSC (makefile) in Hz
  43.    one CPU-Cycle takes 1/F_OSC seconds => 1000000/F_OSC uSeconds
  44.    so: 1 uSecond takes F_OSC/1000000 CPU-Cyles. The following code
  45.    is inspired by the avr-libc delay_loop2 function.
  46.    This it not "that precise" since it takes at least 4 cycles
  47.    but should be o.k. with any parameter (even 0).
  48.    Call function with delayloop(DELAYUS(dt [in uSeconds])).
  49. */
  50.  
  51. #endif
  52.