Arm system counter cleanup
Add some description and cleanup code that uses Arm system counter.
Change-Id: Ie1fe00e3e4b5d98867617b7b0184ac526e333c53
Signed-off-by: Brian Brooks <brian.brooks@arm.com>
diff --git a/src/vppinfra/time.c b/src/vppinfra/time.c
index 770ed8b..1626ff4 100644
--- a/src/vppinfra/time.c
+++ b/src/vppinfra/time.c
@@ -142,17 +142,20 @@
f64
os_cpu_clock_frequency (void)
{
+#if defined (__aarch64__)
+ /* The system counter increments at a fixed frequency. It is distributed
+ * to each core which has registers for reading the current counter value
+ * as well as the clock frequency. The system counter is not clocked at
+ * the same frequency as the core. */
+ u32 hz;
+ asm volatile ("mrs %0, cntfrq_el0":"=r" (hz));
+ return (f64) hz;
+#endif
f64 cpu_freq;
if (clib_cpu_supports_invariant_tsc ())
return estimate_clock_frequency (1e-3);
-#if defined (__aarch64__)
- u64 tsc;
- asm volatile ("mrs %0, CNTFRQ_EL0":"=r" (tsc));
- return (f64) tsc;
-#endif
-
/* First try /sys version. */
cpu_freq = clock_frequency_from_sys_filesystem ();
if (cpu_freq != 0)