[U-Boot] The forbidden value in omap3-common timer.c code

Simon Schwarz schwarz at corscience.de
Thu Apr 21 14:13:38 CEST 2011


Hi there,

I just started to work with the u-boot sources for my bachelor thesis. 
There was a part in the source which irritated me a bit.

I talk about ./arch/arm/cpu/armv7/omap-common/timer.c

It's about that part of code:
#define TIMER_LOAD_VAL  0xffffffff

int timer_init(void)
{
         /* start the counter ticking up, reload value on overflow */
         writel(TIMER_LOAD_VAL, &timer_base->tldr);
         /* enable timer */
         writel((CONFIG_SYS_PTV << 2) | TCLR_PRE | TCLR_AR | TCLR_ST,
&timer_base->tclr);

         reset_timer_masked();   /* init the timestamp and lastinc value */

         return 0;
}


The tldr ist loaded with 0xFFFFFFFF.

The OMAP35x Technical Reference Manual (Rev. P) says on page 2583:
Do not put the overflow value (0xFFFFFFFF) in the GPTi.TLDR register
because it can lead to undesired results.

Is there a reason why the value is used nevertheless? At this time I 
don't know where the timer is used, maybe the "undesired results" 
haven't been noticed yet?

Thanks!
Simon

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