Dear Wolfgang,
On 04.03.2013 12:10, Wolfgang Denk wrote:
Dear Dirk Behme,
In message 1362387637-32334-1-git-send-email-dirk.behme@de.bosch.com you wrote:
From: Dirk Behme dirk.behme@de.bosch.com
Several ARM timer implementations use gd->arch.tbl to record the absolute tick count of 32-bit counters, including timer overflows. For example arch/arm/imx-common/timer.c does:
ulong lastinc; ulong now = counter value; if (no overflow) { ... } else { /* counter overflow */ gd->arch.tbl += (0xFFFFFFFF - lastinc) + now; } lastinc = now;
As we use a 32-bit counter and the two ulong (32-bit) variables 'lastinc' and 'now' here, gd->arch.tbl should be long long (64-bit) to not overflow at the same time, too.
I think this is wrong.
"tbl" means "time base, lower 32 bits" and is complemented by "tbu" (time base, upper 32 bits) to form a 64 bit time base counter.
If you need the full 64 bit precision, then please either maintain the carry manually, or use a proper union or similar.
Many thanks for this explanation!
This patch is obsolete now, replaced by
http://patchwork.ozlabs.org/patch/224740/
Thanks
Dirk