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/*
* linux/arch/arm/mach-at91rm9200/time.c
*
* Copyright (C) 2003 SAN People
* Copyright (C) 2003 ATMEL
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <linux/config.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/time.h>
#include <asm/hardware.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/mach/time.h>
/*
* The ST_CRTR is updated asynchronously to the master clock. It is therefore
* necessary to read it twice (with the same value) to ensure accuracy.
*/
static inline unsigned long read_CRTR(void) {
unsigned long x1, x2;
do {
x1 = at91_sys_read(AT91_ST_CRTR);
x2 = at91_sys_read(AT91_ST_CRTR);
} while (x1 != x2);
return x1;
}
/*
* Returns number of microseconds since last timer interrupt. Note that interrupts
* will have been disabled by do_gettimeofday()
* 'LATCH' is hwclock ticks (see CLOCK_TICK_RATE in timex.h) per jiffy.
* 'tick' is usecs per jiffy (linux/timex.h).
*/
static unsigned long at91rm9200_gettimeoffset(void)
{
unsigned long elapsed;
elapsed = (read_CRTR() - at91_sys_read(AT91_ST_RTAR)) & AT91_ST_ALMV;
return (unsigned long)(elapsed * (tick_nsec / 1000)) / LATCH;
}
/*
* IRQ handler for the timer.
*/
static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
unsigned long rtar;
if (at91_sys_read(AT91_ST_SR) & AT91_ST_PITS) { /* This is a shared interrupt */
write_seqlock(&xtime_lock);
while (((read_CRTR() - at91_sys_read(AT91_ST_RTAR)) & AT91_ST_ALMV) >= LATCH) {
timer_tick(regs);
rtar = (at91_sys_read(AT91_ST_RTAR) + LATCH) & AT91_ST_ALMV;
at91_sys_write(AT91_ST_RTAR, rtar);
}
write_sequnlock(&xtime_lock);
return IRQ_HANDLED;
}
else
return IRQ_NONE; /* not handled */
}
static struct irqaction at91rm9200_timer_irq = {
.name = "at91_tick",
.flags = SA_SHIRQ | SA_INTERRUPT,
.handler = at91rm9200_timer_interrupt
};
/*
* Set up timer interrupt.
*/
void __init at91rm9200_timer_init(void)
{
/* Disable all timer interrupts */
at91_sys_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
(void) at91_sys_read(AT91_ST_SR); /* Clear any pending interrupts */
/*
* Make IRQs happen for the system timer.
*/
setup_irq(AT91_ID_SYS, &at91rm9200_timer_irq);
/* Set initial alarm to 0 */
at91_sys_write(AT91_ST_RTAR, 0);
/* Real time counter incremented every 30.51758 microseconds */
at91_sys_write(AT91_ST_RTMR, 1);
/* Set Period Interval timer */
at91_sys_write(AT91_ST_PIMR, LATCH);
/* Change the kernel's 'tick' value to 10009 usec. (the default is 10000) */
tick_usec = (LATCH * 1000000) / CLOCK_TICK_RATE;
/* Enable Period Interval Timer interrupt */
at91_sys_write(AT91_ST_IER, AT91_ST_PITS);
}
struct sys_timer at91rm9200_timer = {
.init = at91rm9200_timer_init,
.offset = at91rm9200_gettimeoffset,
};
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