VxWorks osdMonotonic implementation

PowerPC time-base frequencies are 32-bit.
Adjust when warnings are printed.
Use long double to calculate time from time-base.

src/libCom/osi/os/vxWorks/osdMonotonic.c

@@ -8,11 +8,11 @@
 #define _VSB_CONFIG_FILE <../lib/h/config/vsbConfig.h>
 
 #include <vxWorks.h>
+#include <stdio.h>
 
 #define EPICS_EXPOSE_LIBCOM_MONOTONIC_PRIVATE
 #include "epicsTypes.h"
 #include "epicsTime.h"
-#include "epicsFindSymbol.h"
 
 
 #define NS_PER_SEC 1000000000
@@ -23,30 +23,35 @@ union timebase {
     UINT64 u64;     /* epicsMonotonicGet() */
 };
 
-static epicsUInt64 ticksPerSec;
-
 
 #if CPU_FAMILY == PPC
 #include <arch/ppc/vxPpcLib.h>
+#include "epicsFindSymbol.h"
+
+/* On PowerPC the timebase counter runs at a rate related to the
+ * bus clock and its frequency should always fit into a UINT32.
+ */
+
+static epicsUInt32 ticksPerSec;
 
 #define TIMEBASEGET(TB) \
     vxTimeBaseGet(&TB.u32[0], &TB.u32[1])
 
-typedef epicsUInt64 (*sysTimeBaseFreq_t)(void);
-
 void osdMonotonicInit(void)
 {
+    typedef epicsUInt32 (*sysTimeBaseFreq_t)(void);
     sysTimeBaseFreq_t sysTimeBaseFreq =
         (sysTimeBaseFreq_t) epicsFindSymbol("_sysTimeBaseFreq");
 
     if (sysTimeBaseFreq) {
         ticksPerSec = sysTimeBaseFreq();
-        return;
-    }
 
-    printf("Warning: BSP routine sysTimeBaseFreq() not found,\n"
-        "can't set up monotonic time source.\n");
-    ticksPerSec = 0;
+        if (!ticksPerSec)
+            printf("Warning: Failed to set up monotonic time source.\n");
+            /* Warn here only if the BSP routine exists but returned 0 */
+    }
+    else
+        ticksPerSec = 0;    /* Warn on first use */
 }
 
 
@@ -55,6 +60,12 @@ void osdMonotonicInit(void)
 #include <arch/i86/pentiumLib.h>
 #include <hwif/cpu/arch/i86/vxCpuIdLib.h>
 
+/* On Intel the timebase counter frequency is returned by the OS as a
+ * UINT64. Some CPUs may count at multi-GHz rates so we need 64 bits.
+ */
+
+static epicsUInt64 ticksPerSec;
+
 #define TIMEBASEGET(TB) \
     pentiumTscGet64(&TB.i64)
 
@@ -68,7 +79,7 @@ void osdMonotonicInit(void)
 
 
 #else
-  #error CPU Family not supported yet!
+  #error This CPU family not supported yet!
 #endif
 
 
@@ -84,9 +95,19 @@ epicsUInt64 epicsMonotonicGet(void)
 {
     union timebase tbNow;
 
-    if (!ticksPerSec)
+    if (!ticksPerSec) {
+        static int warned = 0;
+
+        if (!warned) {
+            printf("Warning: Monotonic time source is not available.\n");
+            warned = 1;
+        }
         return 0;
+    }
 
     TIMEBASEGET(tbNow);
-    return tbNow.u64 / (ticksPerSec / NS_PER_SEC);
+    /* Using a long double for the calculation below to preserve
+     * as many bits in the mantissa as possible.
+     */
+    return ((long double) tbNow.u64) * NS_PER_SEC / ticksPerSec;
 }