From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dirk Behme <dirk.behme@de.bosch.com>
Date: Mon, 4 Mar 2013 15:20:39 +0100
Subject: [U-Boot] [PATCH] ARM: global_data: make tbl long long
In-Reply-To: <20130304111013.01401200246@gemini.denx.de>
References: <1362387637-32334-1-git-send-email-dirk.behme@de.bosch.com>
	<20130304111013.01401200246@gemini.denx.de>
Message-ID: <5134ADB7.2000106@de.bosch.com>
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To: u-boot@lists.denx.de

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This patch is obsolete now, replaced by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