File content as of revision 3:e5d5e2fe4bf6:

/**
 * code from Igor Skochinsky
 * taken from http://mbed.org/forum/mbed/post/799/
*/

#include "semaphore.h"

  Semaphore::Semaphore(): s(SemFree) {};
  
  bool Semaphore::take(bool block)
  {
    int oldval;
#if defined(TARGET_LPC1768) // on Cortex-M3 we can use ldrex/strex
    do {
      // read the semaphore value
      oldval = __ldrex(&s);
      // loop again if it is locked and we are blocking
      // or setting it with strex failed
    }
    while ( (block && oldval == SemTaken) || __strex(SemTaken, &s) != 0 );
    if ( !block ) __clrex(); // clear exclusive lock set by ldrex
#else // on arm7 there's only swp
    do {
      // swp sets the pointed data to the given value and returns the previous one
      oldval = __swp(SemTaken, &s);
      // if blocking, loop until the previous value becomes 0
      // which would mean we have successfully taken the lock
    }
    while (block && oldval == SemTaken);
#endif
    return oldval == SemFree;
  }
  
  // release the semaphore
  void Semaphore::release()
  {
    s = SemFree;
  }