[U-Boot] Timer implementations (was: Re: [PATCH v2] mmc: omap: timeout counter fix)

[Wolfgang Denk]

Dear Reinhard Meyer,

In message <4CC67CA1.9090302 at emk-elektronik.de> you wrote:
> 
> If implemented with true 64 bits for get_ticks() that function is useable
> for timeout programming:
> 
> 	ulong timeval = get_timer (0);
> 
> 	do {
> 		...
> 	} while (get_timer (timeval) < TIMEOUT);
> 
> It appears that the "base" parameter and return value is in CONFIG_SYS_HZ
> units, and not in native ticks. That causes 64 bit mul/div every
> time get_timer() is called. Won't hurt in a timeout loop, though.

But it will hurt in othe rplaces.

Also, this code _is_ a bit different, as "get_timer(0)" makes sure
the counter starts ticking again at 0, and get_timer() is defined to
have millisecond resolution. So you have a guaranteed 2^32
milliseconds or 4294967 seconds or about 3.3 years available which
indeed should be sufficient to implement standard timeouts.

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: wd at denx.de
(null cookie; hope that's ok)