[U-Boot] [RFC] Review of U-Boot timer API

[Wolfgang Denk]

Dear Graeme Russ,

In message <4DDBE22D.6050806 at gmail.com> you wrote:
>
> >> Why must get_timer() be used to perform "meaningful time measurement?"
> > 
> > Excellent question!  It was never intended to be used as such.
> 
> Because get_timer() as it currently stands can as it is assumed to return
> milliseconds

Yes, but without any guarantee for accuracy or resolution.
This is good enough for timeouts, but nothing for time measurements.

> OK, let's wind back - My original suggestion made no claim towards changing
> what the API is used for, or how it looks to those who use it (for all
> practical intents and purposes). I suggested:
>  - Removing set_timer() and reset_timer()
>  - Implement get_timer() as a platform independent function

Trying to remember what I have read in this thread I believe we have
an agreement on these.

> Exposing ticks and tick_frequency to everyone via a 'tick' HAL

I skip this.  I don't even read it.

> =======================
> Not exposing ticks and tick_frequency to everyone
> 
> In /lib/timer.c
> 
> void prescaler(u32 ticks, u32 tick_frequency)
> {
> 	u32 current_ms;
> 
> 	/* Bill's algorithm */
> 
> 	/* result stored in gd->timer_in_ms; */
> }
> 
> In /arch/cpu/soc/timer.c or /arch/cpu/timer.c or /board/<board>/timer.c
> 
> static u32 get_ticks(void)

Currently we have unsigned long long get_ticks(void)  which is better
as it matches existing hardware.

Note that we also have void wait_ticks(u32) as needed for udelay().

> static u32 get_tick_frequency(void)
> {
> 	u32 tick_frequency;
> 
> 	/* Determine tick frequency */
> 
> 	return tick_frequency;
> }

Note that we also have u32 usec2ticks(u32 usec) and u32 ticks2usec(u32 ticks).

Best regards,

Wolfgang Denk

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