一、硬件平台

1.1 控制器：MT7620（A9内核）

1.2 RTC芯片：MCP7940（I2C总线）

二、软件平台

2.1、开发环境：Ubuntu12.04

2.2、软件版本：openwrt 官方15.05版本SDK开发包（CHAOS CALMER 15.05版本）

三、功能说明

本文章所选择的目标芯片为MT7620，profile 选择的为“Xiaomi MiWiFi Mini ”。

3.1、在openwrt 系统上，移植mcp7940的rtc芯片驱动。

3.2、在openwrt系统上，增加对i2c总线的支持。

注意事项：openwrt系统比较奇怪，在menuconfig配置中，配置了i2c，仍然不能支持。需要另外修改“*.dts”文件，才能支持i2c总线。

四、操作步骤

4.1 增加系统对于 i2c 总线的支持

对于系统增加i2c总线的支持，需要修改2个地方

1、openwrt增加对i2c支持。

2、目标芯片的kernel，增加i2c支持。

3、修改dts文件，增加对i2c支持。

4.1.1 配置openwrt 的I2C

在openwrt 目录下，执行“make menuconfig”命令。

进入菜单 Kernel modules  --->I2C support  --->，在菜单选项中，配置如图4-1所示。

图4-1 I2C support

4.1.2 配置目标芯片的 I2C

在openwrt 目录下，执行"make kernel_menuconfig"命令，对目标芯片内核进行配置。

进入菜单， Device Drivers  ---> I2C support  --->，如图4-2所示。

图4-2 目标芯片的I2C总线配置

在图4-2中，选择“I2C Hardware Bus support  ---> ”，配置I2C 硬件总线的支持，选择“Ralink I2C Controller”，如图4-3所示。

图4-3 I2C Hardware Bus support

4.1.3 修改DTS配置文件

默认的openwrt系统，没有对I2C总线的支持，需要自己修改DTS配置文件。由于本文章选择的芯片为MT7620A，目标profile 选择的为“Xiaomi MiWiFi Mini”，故需要修改的文件为“XIAOMI-MIWIFI-MINI.dts”

文件的路径为“openwrt/target/linux/ramips/dts/XIAOMI-MIWIFI-MINI.dts”

修改之前的DTS文件：

        [email protected] {
                gpio0: [email protected] {
                        status = "okay";
                };

                gpio1: [email protected] {
                        status = "okay";
                };

                gpio2: [email protected] {
                        status = "okay";
                };

                [email protected] {
                        status = "okay";

                        [email protected] {

在palmbus节点中，增加MT7620A对I2C总线和RTC芯片的支持，修改之后的DTS文件：

        [email protected] {
                gpio0: [email protected] {
                        status = "okay";
                };

                gpio1: [email protected] {
                        status = "okay";
                };

                gpio2: [email protected] {
                        status = "okay";
                };

                [email protected] {
                        compatible ="ralink,mt7620a-i2c", "ralink,rt2880-i2c";
                        reg= <0x900 0x100>;
                        resets = <&rstctrl 16>;
                        reset-names= "i2c";

                        #address-cells = <1>;
                        #size-cells= <0>;
                        status= "okay";

                        [email protected] {
                                compatible = "mcp,mcp7940";
                                reg = <0x6f>;
                        };
                 };

                [email protected] {
                        status = "okay";

                        [email protected] {

    说明：

1、[email protected]为MT7620A的I2C节点；

2、对于MCP7940芯片，通过查找芯片手册，知道其通信地址为0x6f。如果需要换成其他的芯片，则将对应的地址0x6f都改成其对应的地址即可。

3、对于RTC的名称描述也需要注意，compatible = "mcp,mcp7940"，其中mcp7940对应本文5.1章节，驱动程序rtc_mcp7940.c中第93行，“struct
i2c_device_id”中的名称。如果名字不匹配，则会导致驱动程序执行到probe函数不成功，导致rtc驱动加载失败。

static const struct i2c_device_id mcp7940_id[] = {
        { "mcp7940", mcp7940 },
        { }
};

4、如果I2C的引脚，没有设置，则默认可能工作在GPIO模式，特别注意！在本文中的RTC驱动程序，将I2C的引脚设置为了I2C模式，所以在DTS文件中，就没有再设置I2C引脚的工作模式。如果自己的RTC驱动程序中，没有设置I2C引脚，请在DTS文件中设置其工作为I2C模式，以免它默认工作在GPIO模式中！

                [email protected] {
                        compatible ="ralink,mt7620a-i2c", "ralink,rt2880-i2c";
                        reg= <0x900 0x100>;
                        resets = <&rstctrl 16>;
                        reset-names= "i2c";

                        #address-cells = <1>;
                        #size-cells= <0>;
                        status= "okay";

                        [email protected] {
                                compatible = "mcp,mcp7940";
                                reg = <0x6f>;
                        };
                 };

如果需要修改为ds1307芯片，则只需要将其中的rtc地址和comatible修改即可。ds1307的通信地址为0x68，则修改如下：

                        [email protected] {
                                compatible = "dallas,ds1307";
                                reg = <0x68>;
                        };

4.2 增加对RTC的支持

openwrt系统增加对RTC的支持，需要两个操作：

1、修改target文件，增加RTC支持。

2、修改内核配置，增加RTC支持和配置。

4.2.1 修改target文件

系统在./scripts/medatata.pl中判断并处理RTC_SUPPORT开关，分析之后，原来是在 target/linux/ramips/mt7620/target.mk中，将原始的内容:

FEATURES+=usb

修改为:

FEATURES+=usb rtc

即可打开mt7620对rtc的支持。修改之后，target.mk内容如下：

#
# Copyright (C) 2009 OpenWrt.org
#

SUBTARGET:=mt7620
BOARDNAME:=MT7620 based boards
ARCH_PACKAGES:=ramips_24kec
FEATURES+=usb rtc
CPU_TYPE:=24kec
CPU_SUBTYPE:=dsp

DEFAULT_PACKAGES += kmod-rt2800-pci kmod-rt2800-soc

define Target/Description
        Build firmware images for Ralink MT7620 based boards.
endef

4.2.2 配置内核RTC

1、在openwrt的SDK开发包中，执行“make kernel_menuconfig”命令。

在弹出的菜单“Linux/mips 3.18.29 Kernel Configuration”中，选择“Device Drivers  ---> Real Time Clock  --->”，开启RTC功能选项，如图4-4所示。

图4-4 开启RTC功能

2、进入“ Real Time Clock--->”，对RTC进行配置

配置如图4-5所示，其中：

（1）去除选项“Set system time from RTC on startup and resume”，不再开机的时候就启动RTC驱动，因为本文中，打算开机完毕之后，再自行挂载RTC驱动。如果没有一开始就挂载了RTC驱动，开启这个选项，将出现错误提示“drivers/rtc/hctosys.c:
unable to open rtc device (rtc0)”。

（2）对于“RTC debug support”，依据个人喜好而定，开启之后，可以查看RTC的调试信息。

图4-5 RTC 配置

五、RTC程序

5.1 RTC驱动程序

驱动对应的文件名为：rtc_mcp7940.c，程序如下：

/*
 * rtc-mcp7940.c - RTC driver for some mostly-compatible I2C chips.
 *
 *  Copyright (C) 2005 James Chapman (ds1337 core)
 *  Copyright (C) 2006 David Brownell
 *  Copyright (C) 2009 Matthias Fuchs (rx8025 support)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/string.h>
#include <linux/rtc.h>
#include <linux/bcd.h>

#define RALINK_SYSCTL_BASE		0xB0000000
#define RALINK_TIMER_BASE		0xB0000100
#define RALINK_INTCL_BASE		0xB0000200
#define RALINK_SYSCTL_ADDR      RALINK_SYSCTL_BASE    		// system control
#define RALINK_REG_GPIOMODE     (RALINK_SYSCTL_ADDR + 0x60) // GPIO MODE

#define __devexit
#define __devinitdata
#define __devinit
#define __devexit_p

/* We can't determine type by probing, but if we expect pre-Linux code
 * to have set the chip up as a clock (turning on the oscillator and
 * setting the date and time), Linux can ignore the non-clock features.
 * That's a natural job for a factory or repair bench.
 */
enum ds_type
{
	mcp7940,
};

/* RTC registers don't differ much, except for the century flag */
#define MCP7940_REG_SECS         0x00    /* 00-59 */
#define MCP7940_BIT_CH           0x80
#define MCP7940_BIT_ST           0x80
#define MCP7940_REG_MIN          0x01    /* 00-59 */
#define MCP7940_REG_HOUR         0x02    /* 00-23, or 1-12{am,pm} */
#define MCP7940_BIT_12HR         0x40    /* in REG_HOUR */
#define MCP7940_BIT_PM           0x20    /* in REG_HOUR */
#define MCP7940_REG_WDAY         0x03    /* 01-07 */
#define MCP7940_REG_MDAY         0x04    /* 01-31 */
#define MCP7940_REG_MONTH        0x05    /* 01-12 */
#define MCP7940_REG_YEAR         0x06    /* 00-99 */
#define MCP7940_BIT_VBATEN       0x08

/* Other registers (control, status, alarms, trickle charge, NVRAM, etc)
 * start at 7, and they differ a LOT. Only control and status matter for
 * basic RTC date and time functionality; be careful using them.
 */
#define MCP7940_REG_CONTROL      0x07
#define MCP7940_BIT_OUT          0x80
#define MCP7940_BIT_SQWE         0x10
#define MCP7940_BIT_RS1          0x02
#define MCP7940_BIT_RS0          0x01

struct mcp7940 {
        u8                      offset; /* register's offset */
        u8                      regs[11];
        enum ds_type            type;
        unsigned long           flags;
#define HAS_NVRAM       0               /* bit 0 == sysfs file active */
#define HAS_ALARM       1               /* bit 1 == irq claimed */
        struct i2c_client       *client;
        struct rtc_device       *rtc;
        struct work_struct      work;
        s32 (*read_block_data)(struct i2c_client *client, u8 command,
                               u8 length, u8 *values);
        s32 (*write_block_data)(struct i2c_client *client, u8 command,
                                u8 length, const u8 *values);
};

struct chip_desc {
        unsigned                nvram56:1;
        unsigned                alarm:1;
};

static const struct i2c_device_id mcp7940_id[] = {
        { "mcp7940", mcp7940 },
        { }
};
MODULE_DEVICE_TABLE(i2c, mcp7940_id);

/*----------------------------------------------------------------------*/

#define BLOCK_DATA_MAX_TRIES 10

static s32 mcp7940_read_block_data_once(struct i2c_client *client, u8 command,
                                  u8 length, u8 *values)
{
        s32 i, data;

        for (i = 0; i < length; i++) {
                data = i2c_smbus_read_byte_data(client, command + i);
                if (data < 0)
                        return data;
                values[i] = data;
        }
        return i;
}

static s32 mcp7940_read_block_data(struct i2c_client *client, u8 command,
                                  u8 length, u8 *values)
{
        u8 oldvalues[I2C_SMBUS_BLOCK_MAX];
        s32 ret;
        int tries = 0;

        dev_dbg(&client->dev, "mcp7940_read_block_data (length=%d)\n", length);
        ret = mcp7940_read_block_data_once(client, command, length, values);
        if (ret < 0)
                return ret;
        do {
                if (++tries > BLOCK_DATA_MAX_TRIES) {
                        dev_err(&client->dev,
                                "mcp7940_read_block_data failed\n");
                        return -EIO;
                }
                memcpy(oldvalues, values, length);
                ret = mcp7940_read_block_data_once(client, command, length,
                                                  values);
                if (ret < 0)
                        return ret;
        } while (memcmp(oldvalues, values, length));
        return length;
}

static s32 mcp7940_write_block_data(struct i2c_client *client, u8 command,
                                   u8 length, const u8 *values)
{
    u8 currvalues[I2C_SMBUS_BLOCK_MAX];
    int tries = 0;

    dev_dbg(&client->dev, "mcp7940_write_block_data (length=%d)\n", length);
    do
	{
            s32 i, ret;

            if (++tries > BLOCK_DATA_MAX_TRIES) {
                    dev_err(&client->dev,
                            "mcp7940_write_block_data failed\n");
                    return -EIO;
            }
            for (i = 0; i < length; i++) {
                    ret = i2c_smbus_write_byte_data(client, command + i,
                                                    values[i]);
                    if (ret < 0)
                            return ret;
            }
            ret = mcp7940_read_block_data_once(client, command, length,
                                              currvalues);
            if (ret < 0)
                    return ret;
    } while (memcmp(currvalues, values, length));
    return length;
}

static int mcp7940_get_time(struct device *dev, struct rtc_time *t)
{
        struct mcp7940  *mcp7940 = dev_get_drvdata(dev);
        int             tmp;

        /* read the RTC date and time registers all at once */
        tmp = mcp7940->read_block_data(mcp7940->client,
                mcp7940->offset, 7, mcp7940->regs);
        if (tmp != 7) {
                dev_err(dev, "%s error %d\n", "read", tmp);
                return -EIO;
        }

        dev_dbg(dev, "%s: %02x %02x %02x %02x %02x %02x %02x\n",
                        "read",
                        mcp7940->regs[0], mcp7940->regs[1],
                        mcp7940->regs[2], mcp7940->regs[3],
                        mcp7940->regs[4], mcp7940->regs[5],
                        mcp7940->regs[6]);

        t->tm_sec = bcd2bin(mcp7940->regs[MCP7940_REG_SECS] & 0x7f);
        t->tm_min = bcd2bin(mcp7940->regs[MCP7940_REG_MIN] & 0x7f);
        tmp = mcp7940->regs[MCP7940_REG_HOUR] & 0x3f;
        t->tm_hour = bcd2bin(tmp);
        t->tm_wday = bcd2bin(mcp7940->regs[MCP7940_REG_WDAY] & 0x07) - 1;
        t->tm_mday = bcd2bin(mcp7940->regs[MCP7940_REG_MDAY] & 0x3f);
        tmp = mcp7940->regs[MCP7940_REG_MONTH] & 0x1f;
        t->tm_mon = bcd2bin(tmp) - 1;

        /* assume 20YY not 19YY, and ignore DS1337_BIT_CENTURY */
        t->tm_year = bcd2bin(mcp7940->regs[MCP7940_REG_YEAR]) + 100;

        dev_dbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
                "read", t->tm_sec, t->tm_min,
                t->tm_hour, t->tm_mday,
                t->tm_mon, t->tm_year, t->tm_wday);

        /* initial clock setting can be undefined */
        return rtc_valid_tm(t);
}

static int mcp7940_set_time(struct device *dev, struct rtc_time *t)
{
        struct mcp7940  *mcp7940 = dev_get_drvdata(dev);
        int             result;
        int             tmp;
        u8              *buf = mcp7940->regs;

        dev_dbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
                "write", t->tm_sec, t->tm_min,
                t->tm_hour, t->tm_mday,
                t->tm_mon, t->tm_year, t->tm_wday);

        buf[MCP7940_REG_SECS] = bin2bcd(t->tm_sec);
        buf[MCP7940_REG_MIN] = bin2bcd(t->tm_min);
        buf[MCP7940_REG_HOUR] = bin2bcd(t->tm_hour);
        buf[MCP7940_REG_WDAY] = bin2bcd(t->tm_wday + 1);
        buf[MCP7940_REG_MDAY] = bin2bcd(t->tm_mday);
        buf[MCP7940_REG_MONTH] = bin2bcd(t->tm_mon + 1);

        /* assume 20YY not 19YY */
        tmp = t->tm_year - 100;
        buf[MCP7940_REG_YEAR] = bin2bcd(tmp);

                buf[MCP7940_REG_SECS] |= MCP7940_BIT_ST;
                buf[MCP7940_REG_WDAY] |= MCP7940_BIT_VBATEN;

        dev_dbg(dev, "%s: %02x %02x %02x %02x %02x %02x %02x\n",
                "write", buf[0], buf[1], buf[2], buf[3],
                buf[4], buf[5], buf[6]);

        result = mcp7940->write_block_data(mcp7940->client,
                mcp7940->offset, 7, buf);
        if (result < 0)
		{
                dev_err(dev, "%s error %d\n", "write", result);
                return result;
        }

        return 0;
}

static int mcp7940_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
{
	struct rtc_time time;
	void __user *uarg = (void __user *) arg;

    switch (cmd)
	{
		case RTC_RD_TIME:
			mcp7940_get_time(dev, &time);
			if (copy_to_user(uarg, &time, sizeof(time)))
			{
				printk("RTC_RD_TIME error, can not copy to user\n");
				return -EFAULT;
			}
			break;
		case RTC_SET_TIME:
			if (copy_from_user(&time, uarg, sizeof(time)))
			{
				printk("RTC_SET_TIME error, can not copy from user\n");
				return -EFAULT;
			}
			mcp7940_set_time(dev, &time);
			break;
	    default:
	        return -ENOIOCTLCMD;
    }
    return 0;
}

static const struct rtc_class_ops mcp7940_rtc_ops =
{
	.read_time = mcp7940_get_time,
	.set_time  = mcp7940_set_time,
	.ioctl     = mcp7940_ioctl,
};

/*----------------------------------------------------------------------*/

static struct i2c_driver mcp7940_driver;

static int __devinit mcp7940_probe(struct i2c_client *client,
                                  const struct i2c_device_id *id)
{
    struct mcp7940          *mcp7940;
    int                     err = -ENODEV;
    int                     tmp;
    struct i2c_adapter      *adapter = to_i2c_adapter(client->dev.parent);
    unsigned char           *buf;

    if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA)
        && !i2c_check_functionality(adapter, I2C_FUNC_SMBUS_I2C_BLOCK))
            return -EIO;

    if (!(mcp7940 = kzalloc(sizeof(struct mcp7940), GFP_KERNEL)))
            return -ENOMEM;

    i2c_set_clientdata(client, mcp7940);

    mcp7940->client = client;
    mcp7940->type   = id->driver_data;
    mcp7940->offset = 0;

    buf = mcp7940->regs;
    if (i2c_check_functionality(adapter, I2C_FUNC_SMBUS_I2C_BLOCK)) {
            mcp7940->read_block_data = i2c_smbus_read_i2c_block_data;
            mcp7940->write_block_data = i2c_smbus_write_i2c_block_data;
    } else {
            mcp7940->read_block_data = mcp7940_read_block_data;
            mcp7940->write_block_data = mcp7940_write_block_data;
    }

read_rtc:
        /* read RTC registers */
        tmp = mcp7940->read_block_data(mcp7940->client, 0, 8, buf);
        if (tmp != 8)
		{
                pr_debug("read error %d\n", tmp);
                err = -EIO;
                goto exit_free;
        }

        /* minimal sanity checking; some chips (like DS1340) don't
         * specify the extra bits as must-be-zero, but there are
         * still a few values that are clearly out-of-range.
         */
        tmp = mcp7940->regs[MCP7940_REG_SECS];

                /* make sure that the backup battery is enabled */
                if (!(mcp7940->regs[MCP7940_REG_WDAY] & MCP7940_BIT_VBATEN)) {
                        i2c_smbus_write_byte_data(client, MCP7940_REG_WDAY,
                                mcp7940->regs[MCP7940_REG_WDAY]
                                | MCP7940_BIT_VBATEN);
                }

                /* clock halted?  turn it on, so clock can tick. */
                if (!(tmp & MCP7940_BIT_ST)) {
                        i2c_smbus_write_byte_data(client, MCP7940_REG_SECS,
                                MCP7940_BIT_ST);
                        dev_warn(&client->dev, "SET TIME!\n");
                        goto read_rtc;
                }

        tmp = mcp7940->regs[MCP7940_REG_HOUR];
        switch (mcp7940->type) {
        default:
                if (!(tmp & MCP7940_BIT_12HR))
                        break;

                /* Be sure we're in 24 hour mode.  Multi-master systems
                 * take note...
                 */
                tmp = bcd2bin(tmp & 0x1f);
                if (tmp == 12)
                        tmp = 0;
                if (mcp7940->regs[MCP7940_REG_HOUR] & MCP7940_BIT_PM)
                        tmp += 12;
                i2c_smbus_write_byte_data(client,
                                MCP7940_REG_HOUR,
                                bin2bcd(tmp));
        }

        mcp7940->rtc = rtc_device_register(client->name, &client->dev,
                                &mcp7940_rtc_ops, THIS_MODULE);
        if (IS_ERR(mcp7940->rtc)) {
                err = PTR_ERR(mcp7940->rtc);
                dev_err(&client->dev,
                        "unable to register the class device\n");
                goto exit_free;
        }
    return 0;

exit_free:
        kfree(mcp7940);
        return err;
}

static int __devexit mcp7940_remove(struct i2c_client *client)
{
	struct mcp7940          *mcp7940 = i2c_get_clientdata(client);

    rtc_device_unregister(mcp7940->rtc);
    kfree(mcp7940);
    return 0;
}

static struct i2c_driver mcp7940_driver =
{
    .driver =
	{
        .name   = "rtc-mcp7940",
        .owner  = THIS_MODULE,
    },
    .probe          = mcp7940_probe,
    .remove         = __devexit_p(mcp7940_remove),
    .id_table       = mcp7940_id,
};

static void rtc_pin_mux_init(void)
{
	u32 mode = 0;

	mode = le32_to_cpu(*(volatile u32 *)(RALINK_REG_GPIOMODE));
    mode &= ~(0x1 << 0); 	// I2C_GPIO_MODE引脚，设置为I2C模式，即I2C_SD(GPIO#1)I2C_SCLK(GPIO#2)都设置为I2C模式
    *(volatile u32 *)(RALINK_REG_GPIOMODE) = cpu_to_le32(mode);
}

static int __init mcp7940_init(void)
{
	rtc_pin_mux_init();
    return i2c_add_driver(&mcp7940_driver);
}
module_init(mcp7940_init);

static void __exit mcp7940_exit(void)
{
    i2c_del_driver(&mcp7940_driver);
}
module_exit(mcp7940_exit);

MODULE_AUTHOR("sky.houfei");
MODULE_DESCRIPTION("RTC driver for MCP7940");
MODULE_LICENSE("GPL");

5.2 RTC驱动的makefile

makefile 名称为makefile

############################## mcp7940 rtc driver makefile #########################
obj-m = rtc_mcp7940.o
TARGET_NAME=rtc_mcp7940.ko
PWD=$(shell pwd)
KERNEL_DIR?=/home/sky/develop/openWrt/openwrt/build_dir/target-mipsel_24kec+dsp_glibc-2.21/linux-ramips_mt7620/linux-3.18.29/
TOOL_CAHIN="/home/sky/develop/openWrt/openwrt/staging_dir/toolchain-mipsel_24kec+dsp_gcc-4.8-linaro_glibc-2.21/bin/mipsel-openwrt-linux-gnu-"
OUTPUT_DIR=$(PWD)/../../build_openwrt/mnt/sau2ag1/

###############################################################################
all:
	make -C $(KERNEL_DIR) 	ARCH=mips 	CROSS_COMPILE=$(TOOL_CAHIN)  	M=$(PWD) 	modules

clean:
	rm -f $(obj-m)
	rm -f *.mod.c
	rm -f *.mod.o
	rm -f *.order
	rm -f *.sysvers

#make command:
#make
#make clean

5.3 RTC应用程序

mcp7940应用程序为 rtc_app.c，应用中，存储的时间为UTC格式时间。

对于UTC时间，year = year -1900, month = month -1，应用程序如下。

/*
 *      Real Time Clock Driver Test/Example Program
 *
 *      Compile with:
 *		     gcc -s -Wall -Wstrict-prototypes rtctest.c -o rtctest
 *
 *      Copyright (C) 1996, Paul Gortmaker.
 *
 *      Released under the GNU General Public License, version 2,
 *      included herein by reference.
 *
 */

#include <stdio.h>
#include <linux/rtc.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>

/*
 * This expects the new RTC class driver framework, working with
 * clocks that will often not be clones of what the PC-AT had.
 * Use the command line to specify another RTC if you need one.
 */
static const char default_rtc[] = "/dev/rtc0";

int main(int argc, char **argv)
{
	int i, fd, retval, irqcount = 0;
	unsigned int cmd = 0;
	unsigned long tmp, data;
	struct rtc_time rtc_tm;
	const char *rtc = default_rtc;
	fd = open(default_rtc, O_RDONLY);

	if (fd == -1)
	{
		printf("Can not open %s, exit the app\n", default_rtc);
	}

	rtc_tm.tm_year = 2015 - 1900;
	rtc_tm.tm_mon = 10;
	rtc_tm.tm_mday = 28;
	rtc_tm.tm_wday = 3;
	rtc_tm.tm_hour = 15;
	rtc_tm.tm_min = 22;
	rtc_tm.tm_sec = 10;

	i = atoi(argv[1]);
	switch(i)
	{
		case 1:
			cmd = RTC_RD_TIME;
			break;
		case 2:
			cmd = RTC_SET_TIME;
			printf(	"app set time %d-%d-%d week%d, %02d:%02d:%02d.\n",
				rtc_tm.tm_year + 1900, rtc_tm.tm_mon, rtc_tm.tm_mday, rtc_tm.tm_wday,
				rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);
			break;
		default:
			cmd = RTC_RD_TIME;
			break;
	}

	retval = ioctl(fd, cmd, &rtc_tm);
	if (retval == -1)
	{
		printf("ioctl cmd = %d, error, exit the rtc app\n");
		exit(errno);
	}

	printf(	"rtc app date/time is %d-%d-%d week%d, %02d:%02d:%02d.\n",
				rtc_tm.tm_year + 1900, rtc_tm.tm_mon, rtc_tm.tm_mday, rtc_tm.tm_wday,
				rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);

	close(fd);
	printf("rtc test end\n");
	return 0;
}

六、RTC常见问题分析

6.1 查看是i2c总线是否开启

在MT7620开发板上，输入命令 "ls /dev/i2c*"，如图6-1所示。在图中可以看到i2c-0，说明I2C总线已经开启。

图6-1 查看I2C总线是否开启

说明：如果没有看到i2c设备，则说明系统并未开启i2c总线，不支持i2c总线的操作。此时需要查看下4.1.3章节，dts文件是否修改正确。

6.2 查看I2C总线支持的从机device

在MT7620开发板上，输入命令“ls /sys/bus/i2c/devices/”，如图6-2所示。

在图6-2中，可以看到支持了0x006f的从机设备（mcp7940芯片的地址刚好为0x6f）。

图6-2查看I2C总线支持的从机device

说明：如果没有看到d0x006f或者除了i2c-0之外的设备，则说明i2c总线不支持device从机，此时任何i2c
芯片(从机device)挂载到MT7620上，都不可能通信，因为主机（MT620芯片）不支持从机的地址。此时需要查看下4.1.3章节，dts文件是否修改正确。

6.3 查看i2c总线挂载的驱动

在MT7620开发板上，输入命令“ls /sys/bus/i2c/drivers/”，如图6-3所示。由图可知，设备已经成功将rtc-mcp7940驱动程序挂载至i2c总线。

图6-3 查看i2c总线挂载的驱动

说明：如果没有看到rtc-mcp7940，则说明rtc的驱动程序有问题，需要查看下5.1章节的驱动程序。

6.4 查看rtc设备

在MT7620开发板上，输入命令“ls
/dev/rtc*”，如图6-4所示。由图可知，rtc已经驱动成功，可以看到rtc设备。

图6-4 查看rtc设备

说明：如果没有看到rtc0或者其他的rtc设备，则说明rtc的配置有问题，系统不支持rtc，需要查看下4.2章节的rtc配置。

7、测试

1、挂载rtc驱动

rtc编译后的驱动名称为rtc_mcp7940,执行挂载，提示信息如下，说明rtc成功挂载在0-006f节点下，并且注册为/dev/rtc0：

[email protected]:/tmp# insmod ./rtc_mcp7940.ko
[  203.740000] rtc-mcp7940 0-006f: rtc core: registered mcp7940 as rtc0
[email protected]:/tmp# 

2、运行rtc测试程序

先设置时间，设置完毕之后，再次读取rtc时间，发现可以正常读写时间，且正确。而且将设备重启，重启之后，rtc时间也正常计时，重启过程中，时间没有丢失和停止。

[email protected]:/tmp# ./rtc_app_openwrt 2
app set time 2015-10-28 week3, 15:22:10.
rtc app date/time is 2015-10-28 week3, 15:22:10.
rtc test end

[email protected]:/tmp# ./rtc_app_openwrt 1
rtc app date/time is 2015-10-28 week3, 15:22:26.
rtc test end