1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
|
/*
* linux/arch/arm/mach-at91/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/kernel.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/clockchips.h>
#include <asm/mach/time.h>
#include <asm/arch/at91_st.h>
static unsigned long last_crtr;
static u32 irqmask;
static struct clock_event_device clkevt;
/*
* The ST_CRTR is updated asynchronously to the master clock ... but
* the updates as seen by the CPU don't seem to be strictly monotonic.
* Waiting until we read the same value twice avoids glitching.
*/
static inline unsigned long read_CRTR(void)
{
unsigned long x1, x2;
x1 = at91_sys_read(AT91_ST_CRTR);
do {
x2 = at91_sys_read(AT91_ST_CRTR);
if (x1 == x2)
break;
x1 = x2;
} while (1);
return x1;
}
/*
* IRQ handler for the timer.
*/
static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
{
u32 sr = at91_sys_read(AT91_ST_SR) & irqmask;
/* simulate "oneshot" timer with alarm */
if (sr & AT91_ST_ALMS) {
clkevt.event_handler(&clkevt);
return IRQ_HANDLED;
}
/* periodic mode should handle delayed ticks */
if (sr & AT91_ST_PITS) {
u32 crtr = read_CRTR();
while (((crtr - last_crtr) & AT91_ST_CRTV) >= LATCH) {
last_crtr += LATCH;
clkevt.event_handler(&clkevt);
}
return IRQ_HANDLED;
}
/* this irq is shared ... */
return IRQ_NONE;
}
static struct irqaction at91rm9200_timer_irq = {
.name = "at91_tick",
.flags = IRQF_SHARED | IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
.handler = at91rm9200_timer_interrupt
};
static cycle_t read_clk32k(void)
{
return read_CRTR();
}
static struct clocksource clk32k = {
.name = "32k_counter",
.rating = 150,
.read = read_clk32k,
.mask = CLOCKSOURCE_MASK(20),
.shift = 10,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
static void
clkevt32k_mode(enum clock_event_mode mode, struct clock_event_device *dev)
{
/* Disable and flush pending timer interrupts */
at91_sys_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS);
(void) at91_sys_read(AT91_ST_SR);
last_crtr = read_CRTR();
switch (mode) {
case CLOCK_EVT_MODE_PERIODIC:
/* PIT for periodic irqs; fixed rate of 1/HZ */
irqmask = AT91_ST_PITS;
at91_sys_write(AT91_ST_PIMR, LATCH);
break;
case CLOCK_EVT_MODE_ONESHOT:
/* ALM for oneshot irqs, set by next_event()
* before 32 seconds have passed
*/
irqmask = AT91_ST_ALMS;
at91_sys_write(AT91_ST_RTAR, last_crtr);
break;
case CLOCK_EVT_MODE_SHUTDOWN:
case CLOCK_EVT_MODE_UNUSED:
case CLOCK_EVT_MODE_RESUME:
irqmask = 0;
break;
}
at91_sys_write(AT91_ST_IER, irqmask);
}
static int
clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev)
{
unsigned long flags;
u32 alm;
int status = 0;
BUG_ON(delta < 2);
/* Use "raw" primitives so we behave correctly on RT kernels. */
raw_local_irq_save(flags);
/* The alarm IRQ uses absolute time (now+delta), not the relative
* time (delta) in our calling convention. Like all clockevents
* using such "match" hardware, we have a race to defend against.
*
* Our defense here is to have set up the clockevent device so the
* delta is at least two. That way we never end up writing RTAR
* with the value then held in CRTR ... which would mean the match
* wouldn't trigger until 32 seconds later, after CRTR wraps.
*/
alm = read_CRTR();
/* Cancel any pending alarm; flush any pending IRQ */
at91_sys_write(AT91_ST_RTAR, alm);
(void) at91_sys_read(AT91_ST_SR);
/* Schedule alarm by writing RTAR. */
alm += delta;
at91_sys_write(AT91_ST_RTAR, alm);
raw_local_irq_restore(flags);
return status;
}
static struct clock_event_device clkevt = {
.name = "at91_tick",
.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
.shift = 32,
.rating = 150,
.cpumask = CPU_MASK_CPU0,
.set_next_event = clkevt32k_next_event,
.set_mode = clkevt32k_mode,
};
/*
* ST (system timer) module supports both clockevents and clocksource.
*/
void __init at91rm9200_timer_init(void)
{
/* Disable all timer interrupts, and clear any pending ones */
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);
/* Make IRQs happen for the system timer */
setup_irq(AT91_ID_SYS, &at91rm9200_timer_irq);
/* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used
* directly for the clocksource and all clockevents, after adjusting
* its prescaler from the 1 Hz default.
*/
at91_sys_write(AT91_ST_RTMR, 1);
/* Setup timer clockevent, with minimum of two ticks (important!!) */
clkevt.mult = div_sc(AT91_SLOW_CLOCK, NSEC_PER_SEC, clkevt.shift);
clkevt.max_delta_ns = clockevent_delta2ns(AT91_ST_ALMV, &clkevt);
clkevt.min_delta_ns = clockevent_delta2ns(2, &clkevt) + 1;
clkevt.cpumask = cpumask_of_cpu(0);
clockevents_register_device(&clkevt);
/* register clocksource */
clk32k.mult = clocksource_hz2mult(AT91_SLOW_CLOCK, clk32k.shift);
clocksource_register(&clk32k);
}
struct sys_timer at91rm9200_timer = {
.init = at91rm9200_timer_init,
};
|
