Diff: semaphore.cpp

Revision:

3:e5d5e2fe4bf6

Child:

9:2fe93daa2106

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/semaphore.cpp	Sun Nov 28 22:09:54 2010 +0000
@@ -0,0 +1,39 @@
+/**
+ * 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;
+  }
+  
\ No newline at end of file