1 files changed, 78 insertions, 0 deletions
diff --git a/sem.c b/sem.c
new file mode 100644
index 0000000..c34e798
--- /dev/null
+++ b/sem.c
@@ -0,0 +1,78 @@
+/************************************************************************/
+/*                                                                      */
+/*  File:           sem.c                                               */
+/*  Description:    semaphore P and V operations.                       */
+/*  Version:        1.0                                                 */
+/*  Author:         Otto Mattik                                         */
+/*                                                                      */
+/*  (C)Copyright Otto Mattik 2014-2021.                                 */
+/*                                                                      */
+/*  This file is a part of 'armen' (a tiny operating system).           */
+/*  'armen' is distributed under the CeCILL-V2.1 licence. For more      */
+/*  details about this licence, please visit the website cecill.info    */
+/*                                                                      */
+/************************************************************************/
+
+#ifdef USE_SEM
+
+#include "core.h"
+
+/*
+ * initialize a semaphore
+ *
+ * input:
+ *  sem         address of semaphore
+ *  value       initial value for semaphore
+ * output:
+*/
+void sem_init( sem_t* sem, uint8_t value )
+{
+    ((_sem_t*)sem)->lock = 0;
+    ((_sem_t*)sem)->value =
+    ((_sem_t*)sem)->count = value;
+}
+
+/*
+ * P operation
+ *
+ * input:
+ *  sem         address of semaphore
+ * output:
+ *  O if success, otherwise -1
+*/
+void sem_wait( sem_t* sem )
+{
+    while( test_and_set( sem ) != 0 ) ;
+    if( ((_sem_t*)sem)->count == 0 )
+    {
+        ((_sem_t*)sem)->lock = 0;
+        _threads[_cur_thread].sem = sem;
+        wait_event( EVENT_SEM );
+    }
+    else
+    {
+        --((_sem_t*)sem)->count;
+        ((_sem_t*)sem)->lock = 0;
+    }
+}
+
+/*
+ * V operation
+ *
+ * input:
+ *  sem         address of semaphore
+ * output:
+ *  O if success, otherwise -1
+*/
+void sem_post( sem_t* sem )
+{
+    while( test_and_set( sem ) != 0 ) ;
+    if( ((_sem_t*)sem)->count != ((_sem_t*)sem)->value )
+    {
+        ++((_sem_t*)sem)->count;
+        _wakeup( EVENT_SEM, sem );
+    }
+    ((_sem_t*)sem)->lock = 0;
+}
+
+#endif