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rk27xx: make udelay() more accurate

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Change-Id: Ic448c4e5ec52af6aaeebccee4feea49954394677
This commit is contained in:
Marcin Bukat 2013-04-12 09:27:16 +02:00
parent 6be8097651
commit 3c802a95ed
1 changed files with 2 additions and 8 deletions
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10
firmware/target/arm/rk27xx/system-rk27xx.c
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@ -177,19 +177,13 @@ int system_memory_guard(int newmode)
/* usecs may be at most 2^32/200 (~21 seconds) for 200MHz max cpu freq */
void udelay(unsigned usecs)
{
unsigned cycles_per_usec;
unsigned delay;
if (cpu_frequency == CPUFREQ_MAX) {
cycles_per_usec = (CPUFREQ_MAX + 999999) / 1000000;
} else {
cycles_per_usec = (CPUFREQ_NORMAL + 999999) / 1000000;
}
delay = (usecs * cycles_per_usec + 3) / 4;
delay = (usecs * (cpu_frequency/1000000)) / 5;
asm volatile(
"1: subs %0, %0, #1 \n" /* 1 cycle */
" nop \n" /* 1 cycle */
" bne 1b \n" /* 3 cycles */
: : "r"(delay)
);