At Clock_exit, mask timer interrupts instead of just disabling them

c/src/lib/libbsp/patmos/shared/clock/ckinit.c

@@ -378,6 +378,10 @@ void Install_clock(
 
 void Clock_exit( void )
 {
+	/* mask interrupt */
+
+	intr_mask(EXC_INTR_USEC);
+
 	/* turn off the timer interrupts */
 
 	patmos_disable_interrupts();

c/src/lib/libcpu/patmos/exceptions/exceptions.c

@@ -55,9 +55,17 @@ void intr_clear_all_pending(void){
 }
 
 /*
- * Unmask a particular interrupts
+ * Unmask a particular interrupt
  * 	 n - The interrupt to be unmasked
  */
 void intr_unmask(unsigned n){
   EXC_MASK |= (1 << n);
 }
+
+/*
+ * Mask a particular interrupt
+ * 	 n - The interrupt to be masked
+ */
+void intr_mask(unsigned n){
+  EXC_MASK &= ~(1 << n);
+}

c/src/lib/libcpu/patmos/exceptions/exceptions.h

@@ -42,6 +42,8 @@ void intr_clear_all_pending(void);
 
 void intr_unmask(unsigned n);
 
+void intr_mask(unsigned n);
+
 #endif
 
 /* end of include file */