2 * linux/arch/arm/mach-at91rm9200/time.c
4 * Copyright (C) 2003 SAN People
5 * Copyright (C) 2003 ATMEL
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
22 #include <linux/config.h>
23 #include <linux/init.h>
24 #include <linux/interrupt.h>
25 #include <linux/kernel.h>
26 #include <linux/sched.h>
27 #include <linux/time.h>
29 #include <asm/hardware.h>
32 #include <asm/mach/time.h>
35 * The ST_CRTR is updated asynchronously to the master clock. It is therefore
36 * necessary to read it twice (with the same value) to ensure accuracy.
38 static inline unsigned long read_CRTR(void) {
42 x1
= at91_sys_read(AT91_ST_CRTR
);
43 x2
= at91_sys_read(AT91_ST_CRTR
);
50 * Returns number of microseconds since last timer interrupt. Note that interrupts
51 * will have been disabled by do_gettimeofday()
52 * 'LATCH' is hwclock ticks (see CLOCK_TICK_RATE in timex.h) per jiffy.
53 * 'tick' is usecs per jiffy (linux/timex.h).
55 static unsigned long at91rm9200_gettimeoffset(void)
57 unsigned long elapsed
;
59 elapsed
= (read_CRTR() - at91_sys_read(AT91_ST_RTAR
)) & AT91_ST_ALMV
;
61 return (unsigned long)(elapsed
* (tick_nsec
/ 1000)) / LATCH
;
65 * IRQ handler for the timer.
67 static irqreturn_t
at91rm9200_timer_interrupt(int irq
, void *dev_id
, struct pt_regs
*regs
)
71 if (at91_sys_read(AT91_ST_SR
) & AT91_ST_PITS
) { /* This is a shared interrupt */
72 write_seqlock(&xtime_lock
);
76 rtar
= (at91_sys_read(AT91_ST_RTAR
) + LATCH
) & AT91_ST_ALMV
;
77 at91_sys_write(AT91_ST_RTAR
, rtar
);
78 } while (((read_CRTR() - at91_sys_read(AT91_ST_RTAR
)) & AT91_ST_ALMV
) >= LATCH
);
80 write_sequnlock(&xtime_lock
);
85 return IRQ_NONE
; /* not handled */
88 static struct irqaction at91rm9200_timer_irq
= {
90 .flags
= SA_SHIRQ
| SA_INTERRUPT
,
91 .handler
= at91rm9200_timer_interrupt
95 * Set up timer interrupt.
97 void __init
at91rm9200_timer_init(void)
99 /* Disable all timer interrupts */
100 at91_sys_write(AT91_ST_IDR
, AT91_ST_PITS
| AT91_ST_WDOVF
| AT91_ST_RTTINC
| AT91_ST_ALMS
);
101 (void) at91_sys_read(AT91_ST_SR
); /* Clear any pending interrupts */
104 * Make IRQs happen for the system timer.
106 setup_irq(AT91_ID_SYS
, &at91rm9200_timer_irq
);
108 /* Set initial alarm to 0 */
109 at91_sys_write(AT91_ST_RTAR
, 0);
111 /* Real time counter incremented every 30.51758 microseconds */
112 at91_sys_write(AT91_ST_RTMR
, 1);
114 /* Set Period Interval timer */
115 at91_sys_write(AT91_ST_PIMR
, LATCH
);
117 /* Change the kernel's 'tick' value to 10009 usec. (the default is 10000) */
118 tick_usec
= (LATCH
* 1000000) / CLOCK_TICK_RATE
;
120 /* Enable Period Interval Timer interrupt */
121 at91_sys_write(AT91_ST_IER
, AT91_ST_PITS
);
124 struct sys_timer at91rm9200_timer
= {
125 .init
= at91rm9200_timer_init
,
126 .offset
= at91rm9200_gettimeoffset
,