Use nrf_delay_us in delayMicroseconds

cores/nRF5/delay.h

@@ -25,6 +25,8 @@ extern "C" {
 
 #include <stdint.h>
 
+#include "nrf_delay.h"
+
 #include "variant.h"
 
 /**
@@ -69,33 +71,7 @@ static __inline__ void delayMicroseconds( uint32_t usec )
     return ;
   }
 
-  /*
-   *  The following loop:
-   *
-   *    for (; ul; ul--) {
-   *      __asm__ volatile("");
-   *    }
-   *
-   *  produce the following assembly code:
-   *
-   *    loop:
-   *      subs r3, #1        // 1 Core cycle
-   *      bne.n loop         // 1 Core cycle + 1 if branch is taken
-   */
-
-  // VARIANT_MCK / 1000000 == cycles needed to delay 1uS
-  //                     3 == cycles used in a loop
-  uint32_t n = usec * (VARIANT_MCK / 1000000) / 3;
-  __asm__ __volatile__(
-    "1:              \n"
-    "   sub %0, #1   \n" // substract 1 from %0 (n)
-    "   bne 1b       \n" // if result is not 0 jump to 1
-    : "+r" (n)           // '%0' is n variable with RW constraints
-    :                    // no input
-    :                    // no clobber
-  );
-  // https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
-  // https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Volatile
+  nrf_delay_us(usec);
 }
 
 #ifdef __cplusplus