new tool: chrono (wip)

1 files changed, 38 insertions, 0 deletions

diff --git a/nanosec.c b/nanosec.c
new file mode 100644
index 0000000..1301e9f
--- /dev/null
+++ b/nanosec.c
@@ -0,0 +1,38 @@
+#include <u.h>
+#include <libc.h>
+#include <tos.h>
+
+/*
+ * nsec() is wallclock and can be adjusted by timesync
+ * so need to use cycles() instead, but fall back to
+ * nsec() in case we can't
+ */
+uvlong
+nanosec(void)
+{
+	static uvlong fasthz, xstart;
+	uvlong x, div;
+
+	if(fasthz == ~0ULL)
+		return nsec() - xstart;
+
+	if(fasthz == 0){
+		if(_tos->cyclefreq){
+			cycles(&xstart);
+			fasthz = _tos->cyclefreq;
+		} else {
+			xstart = nsec();
+			fasthz = ~0ULL;
+			fprint(2, "cyclefreq not available, falling back to nsec()\n");
+			fprint(2, "you might want to disable aux/timesync\n");
+			return 0;
+		}
+	}
+	cycles(&x);
+	x -= xstart;
+
+	/* this is ugly */
+	for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL);
+
+	return x / (fasthz / div);
+}