Dear Stephen,
In message <51d45f4d.2010...@wwwdotorg.org> you wrote:
>
> > get_timer() is used by a number of network related services. For
> > information, just grep for it in the net/ and drivers/net/
> > directories. The "get_timer(0)" used in your code resets a global
> > resource, and has thus the potential of messing up a number of
> > timeouts running elsewhere in the network code. I wonder to which
> > extend this has actually been considered (and tested) ?
>
> I recall you mentioning this before, but can you expand on this a bit
> please?
>
> For the two platforms I'm familiar with (Tegra and BCM2835), the
> implementation of get_timer() is simply:
>
> unlong get_timer(ulong base)
> {
> ulong time = read_hw_register()
> time -= base;
> return time;
> }
>
> There's no global state involved. Is this implementation of get_timer()
> wrong somehow? I'm having a hard time envisaging what kind of global
> state it's supposed to maintain.
It appears you are (basically) right. Eventually I remember an old
implementation that has been fixed since.
I checked all implementations I could find (all 102 of them) and they
all behave as you showed in your example, i. e. harmless.
An exception is "arch/arm/cpu/sa1100/timer.c" which does not respect
the "base" argument at all, i. e. which is broken.
> I always thought that every user of get_timer() was supposed to do
> something like:
>
> ulong base = get_timer(0);
> ... work to be timed
> ulong time_diff = get_timer(base);
>
> in other words, every user maintains their own base variable, and hence
> get_timer(0) doesn't affect any other users.
Yes, you are right. Sorry for causing confusion here.
Best regards,
Wolfgang Denk
--
DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: w...@denx.de
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