002-clock-overflow

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

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 guarentee 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).

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

1 files changed, 1 insertions, 1 deletions

diff --git a/common/clock.c b/common/clock.c
index 4069d4e83b..e22b6a5409 100644
--- a/common/clock.c
+++ b/common/clock.c
@@ -41,7 +41,7 @@ uint64_t get_time_ns(void)
         uint64_t ns_offset;
 
         /* read clocksource: */
-        cycle_now = cs->read();
+	cycle_now = cs->read() & cs->mask;
 
         /* calculate the delta since the last call: */
         cycle_delta = (cycle_now - cs->cycle_last) & cs->mask;