[U-Boot] [RFC][Timer API] Revised Specification - Implementation details

Graeme Russ
2011-06-15T13:17:20Z

Hi Wolfgang,

Since discussion seems to have died down, I have assumed pseudo consensus
and have started hitting the timer cleanup in earnest. All I can say is:

Wow! What a mess ;)

> We could also design a more complicated API like this one, but I doubt
> this is needed:

Well, it is needed if you are measuring how long something has taken (say
erasing a Flash, performing an I/O operation, profiling boot-up etc)

>
> /*
> * round - used to control rounding:
> * <0 : round down, return time that has passed AT LEAST
> * =0 : don't round, provide raw time difference
> * >0 : round up, return time that has passed AT MOST
> */
> u32 delta_timer(u32 from, u32 to, int round)
> {

[snip]

> }

I decided to implement three separate functions:

u32 time_ms_delta_min(u32 from, u32 to)
u32 time_ms_delta_max(u32 from, u32 to)
u32 time_ms_delta_raw(u32 from, u32 to)

So if you only use one, the rest get stripped out of the binary

The ms_ part allows for:

u32 time_us_delta_min(u32 from, u32 to)
u32 time_us_delta_max(u32 from, u32 to)
u32 time_us_delta_raw(u32 from, u32 to)

I intend to let the time_us_delta* functions drop to ms resolution of the
underlying tick counter is not sub-millisecond. Where the tick counter is
microsecond (or better), then arch-specific udelay becomes a trivial
implementation of a loop using time_us_now() and time_us_delta_min() -
Actually, we can make this a weak default and have arches with a non
microsecond tick counter override it.

> So our timeout from case 1) above would now be written like this:
>
> u32 start,now;
> u32 timeout = 5 * CONFIG_SYS_HZ; /* timeout after 5 seconds */
>
> start = get_timer(0);

I now have:
start = time_ms_now();

>
> while (test_for_event() == 0) {
> now = get_timer(0);
>
> if (delta_timer(start, now) > timeout)
> handle_timeout();
>
> udelay(100);
> }
>
> and would be guaranteed never to terminate early.
>
>
>
> Comments?

With the 'time_ms_' prefix, it's starting to get rather long, and I'm
pushing a lot of timeout checks beyond 80 columns - especially when
existing code has variables like 'start_time_tx' - I'm starting to consider
dropping the time_ prefix (all time functions will still have a ms_ or us_
prefix anyway) and rename a lot of variables

Thoughts?

Regards,

Graeme