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
|
/*
* rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
*
* Copyright (c) 2008 by David Brownell
*
* 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.
*/
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/rtc.h>
#include <linux/platform_device.h>
#include <linux/i2c/dm355evm_msp.h>
/*
* The MSP430 firmware on the DM355 EVM uses a watch crystal to feed
* a 1 Hz counter. When a backup battery is supplied, that makes a
* reasonable RTC for applications where alarms and non-NTP drift
* compensation aren't important.
*
* The only real glitch is the inability to read or write all four
* counter bytes atomically: the count may increment in the middle
* of an operation, causing trouble when the LSB rolls over.
*
* This driver was tested with firmware revision A4.
*/
union evm_time {
u8 bytes[4];
u32 value;
};
static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm)
{
union evm_time time;
int status;
int tries = 0;
do {
/*
* Read LSB(0) to MSB(3) bytes. Defend against the counter
* rolling over by re-reading until the value is stable,
* and assuming the four reads take at most a few seconds.
*/
status = dm355evm_msp_read(DM355EVM_MSP_RTC_0);
if (status < 0)
return status;
if (tries && time.bytes[0] == status)
break;
time.bytes[0] = status;
status = dm355evm_msp_read(DM355EVM_MSP_RTC_1);
if (status < 0)
return status;
if (tries && time.bytes[1] == status)
break;
time.bytes[1] = status;
status = dm355evm_msp_read(DM355EVM_MSP_RTC_2);
if (status < 0)
return status;
if (tries && time.bytes[2] == status)
break;
time.bytes[2] = status;
status = dm355evm_msp_read(DM355EVM_MSP_RTC_3);
if (status < 0)
return status;
if (tries && time.bytes[3] == status)
break;
time.bytes[3] = status;
} while (++tries < 5);
dev_dbg(dev, "read timestamp %08x\n", time.value);
rtc_time_to_tm(le32_to_cpu(time.value), tm);
return 0;
}
static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
union evm_time time;
unsigned long value;
int status;
rtc_tm_to_time(tm, &value);
time.value = cpu_to_le32(value);
dev_dbg(dev, "write timestamp %08x\n", time.value);
/*
* REVISIT handle non-atomic writes ... maybe just retry until
* byte[1] sticks (no rollover)?
*/
status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
if (status < 0)
return status;
status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
if (status < 0)
return status;
status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
if (status < 0)
return status;
status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
if (status < 0)
return status;
return 0;
}
static struct rtc_class_ops dm355evm_rtc_ops = {
.read_time = dm355evm_rtc_read_time,
.set_time = dm355evm_rtc_set_time,
};
/*----------------------------------------------------------------------*/
static int __devinit dm355evm_rtc_probe(struct platform_device *pdev)
{
struct rtc_device *rtc;
rtc = rtc_device_register(pdev->name,
&pdev->dev, &dm355evm_rtc_ops, THIS_MODULE);
if (IS_ERR(rtc)) {
dev_err(&pdev->dev, "can't register RTC device, err %ld\n",
PTR_ERR(rtc));
return PTR_ERR(rtc);
}
platform_set_drvdata(pdev, rtc);
return 0;
}
static int __devexit dm355evm_rtc_remove(struct platform_device *pdev)
{
struct rtc_device *rtc = platform_get_drvdata(pdev);
rtc_device_unregister(rtc);
platform_set_drvdata(pdev, NULL);
return 0;
}
/*
* I2C is used to talk to the MSP430, but this platform device is
* exposed by an MFD driver that manages I2C communications.
*/
static struct platform_driver rtc_dm355evm_driver = {
.probe = dm355evm_rtc_probe,
.remove = __devexit_p(dm355evm_rtc_remove),
.driver = {
.owner = THIS_MODULE,
.name = "rtc-dm355evm",
},
};
static int __init dm355evm_rtc_init(void)
{
return platform_driver_register(&rtc_dm355evm_driver);
}
module_init(dm355evm_rtc_init);
static void __exit dm355evm_rtc_exit(void)
{
platform_driver_unregister(&rtc_dm355evm_driver);
}
module_exit(dm355evm_rtc_exit);
MODULE_LICENSE("GPL");
|
