[U-Boot-Users] [Patch 02/17] U-Boot-V2:Common:Clock Handle case of clock rollover for get_time_ns

Menon, Nishanth
2008-05-21T16:25:15Z

get_time_ns does a simplistic delta = cycle_now - cycle_last. It is possible that the h/w counter reached max and reset back to 0.
This patch addresses this issue by checking for rollover condition.

NOTE 1: This does not guarantee that you cannot confuse get_time_ns. You could possibly wait for two reset cycles and then get a messed up value.
To fix that we may need interrupt mode timer tick - something on the lines of jiffies on linux.
NOTE 2: the question of cs->mask is not clear. if the mask is for the tick, then it is better done with (cycle_now & cs->mask) - (cs->cycle_last & cs->mask). Do we need min and max for register read?

Signed-off-by: Nishanth Menon<x0nishan@ti.com>

---
common/clock.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

Index: u-boot-v2.git/common/clock.c
===================================================================
--- u-boot-v2.git.orig/common/clock.c 2008-05-20 17:19:44.000000000 -0500
+++ u-boot-v2.git/common/clock.c 2008-05-20 17:26:31.000000000 -0500
@@ -37,14 +37,24 @@
uint64_t get_time_ns(void)
{
struct clocksource *cs = current_clock;
- uint64_t cycle_now, cycle_delta;
+ uint64_t cycle_now, cycle_delta = 0;
uint64_t ns_offset;

/* read clocksource: */
cycle_now = cs->read();

/* calculate the delta since the last call: */
- cycle_delta = (cycle_now - cs->cycle_last) & cs->mask;
+
+ /* Handle rollover case */
+ if (cycle_now < cs->cycle_last) {
+ /* FIXME: I am not convinced about the cs->mask operation..
+ * I am assuming cs->mask is max! Probably need to change
+ * clocksource structure to have min and max
+ */
+ cycle_delta = cs->mask - (cs->cycle_last & cs->mask);
+ cs->cycle_last = 0;
+ }
+ cycle_delta += (cycle_now & cs->mask) - (cs->cycle_last & cs->mask);

/* convert to nanoseconds: */
ns_offset = cyc2ns(cs, cycle_delta);