rx8900 软件包是针对RT-Thread驱动框架实现的实时时钟驱动，遵循RT-Thread RTC框架，可以从芯片内置RTC无缝切换使用外置高精度rx8900 RTC。rx8900是爱普生公司一款i2c接口的高精度RTC芯片，集成32768Hz晶振和温度传感器，并能根据环境温度调整频率，具有供电范围灵活、待机电流低、走时精度高等优点。
| 名称 | 说明 |
|---|---|
| docs | 文档目录 |
| inc | 头文件目录 |
| src | 源代码目录 |
| LICENSE | 许可证文件 |
| SConscript | RT-Thread默认构建脚本 |
rx8900 软件包遵循 Apache license v2.0 许可，详见 LICENSE 文件。
实现rx8900驱动层的函数接口。
RT-Thread rtc驱动设备继承其标准设备驱动，使用struct rt_device描述rx8900设备。rx8900访问接口是i2c，依赖于RT-Thread i2c总线框架，我们使用struct rt_device的私有数据user_data保存rx8900的i2c设备总线信息。后面过程则是实现struct rt_device函数指针实体。
/*** Device structure*/
struct rt_device
{struct rt_object parent; /**< inherit from rt_object */enum rt_device_class_type type; /**< device type */rt_uint16_t flag; /**< device flag */rt_uint16_t open_flag; /**< device open flag */rt_uint8_t ref_count; /**< reference count */rt_uint8_t device_id; /**< 0 - 255 *//* device call back */rt_err_t (*rx_indicate)(rt_device_t dev, rt_size_t size);rt_err_t (*tx_complete)(rt_device_t dev, void *buffer);#ifdef RT_USING_DEVICE_OPSconst struct rt_device_ops *ops;
#else/* common device interface */rt_err_t (*init) (rt_device_t dev);rt_err_t (*open) (rt_device_t dev, rt_uint16_t oflag);rt_err_t (*close) (rt_device_t dev);rt_size_t (*read) (rt_device_t dev, rt_off_t pos, void *buffer, rt_size_t size);rt_size_t (*write) (rt_device_t dev, rt_off_t pos, const void *buffer, rt_size_t size);rt_err_t (*control)(rt_device_t dev, int cmd, void *args);
#endif#if defined(RT_USING_POSIX)const struct dfs_file_ops *fops;struct rt_wqueue wait_queue;
#endifvoid *user_data; /**< device private data */
};
static struct rt_device rx8900_dev; /* rx8900 device */
static rt_err_t rx8900_write_reg(rt_device_t dev, rt_uint8_t reg, rt_uint8_t *data, rt_uint8_t data_size)
static rt_err_t rx8900_write_reg(rt_device_t dev, rt_uint8_t reg, rt_uint8_t *data, rt_uint8_t data_size)
RT-Thread设备虚拟文件接口，常用有open/read/write/control/close，RT-Thread rtc设备框架中，关于时间和闹钟的设置，使用的是control接口，实现该接口具体功能内容。
/* get time */case RT_DEVICE_CTRL_RTC_GET_TIME:time = (time_t *)args;ret = rx8900_read_reg(dev, REG_SEC, buff, 7);if(ret == RT_EOK){time_temp.tm_year = bcd_to_hex(buff[6]) + 2000 - 1900;time_temp.tm_mon = bcd_to_hex(buff[5]&0x1f) - 1;time_temp.tm_mday = bcd_to_hex(buff[4]&0x3f);time_temp.tm_hour = bcd_to_hex(buff[2]&0x3f);time_temp.tm_min = bcd_to_hex(buff[1]&0x7f);time_temp.tm_sec = bcd_to_hex(buff[0]&0x7f);*time = mktime(&time_temp);}break;
/* set time */case RT_DEVICE_CTRL_RTC_SET_TIME:{struct tm *time_new;time = (time_t *)args;time_new = localtime(time);buff[6] = hex_to_bcd(time_new->tm_year + 1900 - 2000);buff[5] = hex_to_bcd(time_new->tm_mon + 1);buff[4] = hex_to_bcd(time_new->tm_mday);buff[3] = hex_to_bcd(time_new->tm_wday+1);buff[2] = hex_to_bcd(time_new->tm_hour);buff[1] = hex_to_bcd(time_new->tm_min);buff[0] = hex_to_bcd(time_new->tm_sec);ret = rx8900_write_reg(dev, REG_SEC, buff, 7);}break;
rx8900闹钟模式支持的最小精度是1分钟，因此闹钟秒数值（tm_sec）应设置为0。rx8900支持天数和星期闹钟，RT-Thread目前闹钟框架暂时支持时分秒匹配，天数和星期由软件实现。
/* get alarm time */case RT_DEVICE_CTRL_RTC_GET_ALARM:{ struct rt_rtc_wkalarm *alm_time;rt_uint8_t state[3] = {0x00}; ret = rx8900_read_reg(dev, REG_ALM_MIN, buff, 2);if(ret != RT_EOK){return -RT_ERROR;}alm_time = (struct rt_rtc_wkalarm *)args;alm_time->tm_hour = bcd_to_hex(buff[1]&0x7f); alm_time->tm_min = bcd_to_hex(buff[0]&0x7f);alm_time->tm_sec = 0; /* hardware alarm precision is 1 minute */ret = rx8900_read_reg(dev, RGE_EXT, state, 3);if(ret != RT_EOK){return -RT_ERROR;}if (state[0] & VALUE_EXT_WADA){/* day alarm *//* todo, RTT not supported temporarily */ }else{/* week day alarm *//* todo, RTT not supported temporarily */}}
针对RT-Thread闹钟框架，rx8900闹钟禁止天数（tm_day）和星期（tm_wday）匹配功能，只设置小时（tm_hour）和分钟（tm_minute），同时将秒数（tm_sec）设为0。
/* set alarm time */case RT_DEVICE_CTRL_RTC_SET_ALARM:{struct rt_rtc_wkalarm *alm_time;rt_uint8_t ctrl[2] = {0x00};alm_time = (struct rt_rtc_wkalarm *)args;buff[2] = ALM_DISABLE(0x00); /* week and day alarm disable */ buff[1] = hex_to_bcd(ALM_ENABLE(alm_time->tm_hour));/* enable, alarm when hours and minutes match */buff[0] = hex_to_bcd(ALM_ENABLE(alm_time->tm_min));ret = rx8900_read_reg(dev, REG_FLAG, ctrl, 2);if (ret != RT_EOK){return -RT_ERROR;}if (ctrl[0]&VALUE_EXT_WADA){/* day alarm *//* todo, RTT not supported temporarily */}else{/* week day alarm *//* todo, RTT not supported temporarily */}/* write to hardware */ret = rx8900_write_reg(dev, REG_ALM_MIN, buff, 3);if (ret != RT_EOK){return -RT_ERROR;}/* clear alarm flag */ctrl[1] &= ~VALUE_FLAG_AF;ret = rx8900_write_reg(dev, REG_FLAG, &ctrl[1], 1);}break;
rx8900内部集成一个温度传感器和温度校准系数，读取温度寄存器值通过一定的换算公式计算出实际温度。rx8900芯片手册提供摄氏度（℃）与寄存器值转换公式如下。
获取温度接口
/** @brief Read temperature from rx8900* @return Celsius temperature,-55~+125C,0.1C */
float rx8900_get_temperature(void)
{rt_uint8_t value = 0;float temp = 0.0f;rx8900_read_reg(&rx8900_dev, REG_TEMP, (rt_uint8_t*)&value, 1);temp = (value*2-187.19)/3.218;return temp;
}
我们把温度读取接口注册到RT-Thread的调试终端（msh/finsh），方便测试。
#ifdef RT_USING_FINSH
#include <finsh.h>void list_rx89_temp(void)
{float temp = 0.0f;temp = rx8900_get_temperature();rt_kprintf("rx8900 temperature: [%d.%dC] \n", (int)temp, (int)(temp * 10) % 10);
}
FINSH_FUNCTION_EXPORT(list_rx89_temp, list rx8900 temperature.)
#endif /* RT_USING_FINSH */#if defined(RT_USING_FINSH) && defined(FINSH_USING_MSH)
MSH_CMD_EXPORT(list_rx89_temp, list rx8900 temperature.);
#endif /* RT_USING_FINSH & FINSH_USING_MSH */
“i2c1”，i2c1驱动请自行初始化注册；否则rx8900设备注册失败user_data保存i2c1总线信息，用于后续访问rx8900“rtc”int rt_hw_rx8900_init(void)
{ struct rt_i2c_bus_device *i2c_bus =RT_NULL;rt_uint8_t flags = 0;rt_bool_t need_clear = RT_FALSE;rt_bool_t need_reset = RT_FALSE;i2c_bus = rt_i2c_bus_device_find(RX8900_I2C_BUS);if (i2c_bus == RT_NULL){LOG_E("i2c bus device %s not found!\r\n", RX8900_I2C_BUS);return -RT_ERROR;} /* register rtc device */rx8900_dev.type = RT_Device_Class_RTC;rx8900_dev.init = RT_NULL;rx8900_dev.open = rt_rx8900_open;rx8900_dev.close = RT_NULL;rx8900_dev.read = rt_rx8900_read;rx8900_dev.write = RT_NULL;rx8900_dev.control = rt_rx8900_control;rx8900_dev.user_data= (void*)i2c_bus; /* save i2cbus */rt_device_register(&rx8900_dev, RX8900_DEVICE_NAME, RT_DEVICE_FLAG_RDWR);......
}
rx8900私有信息初始化主要包括：
if (flags & VALUE_FLAG_VDET){LOG_D("Temperature compensation stop detected.\n");need_clear = RT_TRUE;}/* alarm */if (flags & VALUE_FLAG_AF) { LOG_D("Alarm was detected.\n");need_clear = RT_TRUE;}/* timer */if (flags & VALUE_FLAG_TF) { LOG_D("Timer was detected.\n");need_clear = RT_TRUE;}......
使用 rx8900 package， 需要在 RT-Thread 的包管理器中选择它，具体路径如下：
RT-Thread online packages --->peripheral libraries and drivers --->[*] extren rtc drivers --->[*] rx8900：Extern RTC drivers fo rx8900 Version (latest) --->
然后让 RT-Thread 的包管理器自动更新，或者执行 pkgs --update 命令更新包到 BSP 中。
首先需初始化rx8900 驱动，可以手动在初始化线程合适的地方调用rt_hw_rx8900 _init()初始化，也可以直接使用INIT_DEVICE_EXPORT通过RT-Thread的自动初始化机制来初始化注册。初始化成功后，会注册名称为“rtc”的驱动设备。
INIT_DEVICE_EXPORT(rt_hw_rx8900_init); /* 通过RTT的自动初始化机制初始化rx8900 */
注：
如果开启了芯片内部RTC，需先禁止内部RTC
查看设备是否注册成功。
对于时间和闹钟的访问，使用RT-Thread标准RTC和闹钟接口访问。片内温度读取，则由软件包提供一个函数接口。
time_t time(time_t *t)
time_t now;
now = time(RT_NULL);
#define RT_DEVICE_CTRL_RTC_SET_TIME 0x11 /**< set time */rt_err_t rt_device_control(rt_device_t dev, int cmd, void *arg)；
#define RT_DEVICE_CTRL_RTC_GET_ALARM 0x12 /**< get alarm */rt_err_t rt_device_control(rt_device_t dev, int cmd, void *arg)；
#define RT_DEVICE_CTRL_RTC_SET_ALARM 0x13 /**< set alarm */rt_err_t rt_device_control(rt_device_t dev, int cmd, void *arg)；
注：
详细用法可以参考“/components/drivers/rtc.c”和“/components/drivers/alarm.c”源码。
float rx8900_get_temperature(void)；
msh >date
Sat Jan 1 00:00:04 2000
msh date 2020 04 10 17 41 10
msh >date
Fri Apr 10 17:41:15 2020
finsh >list_date()
Fri Apr 10 17:41:49 2020
finsh >set_date(2020,5,1)0, 0x00000000
finsh >set_time(12,0,0) 0, 0x00000000
finsh >list_date()
Fri May 1 12:00:04 2020
msh >list_rx89_temp
rx8900 temperature: [27.5C]
finsh >list_rx89_temp()
rx8900 temperature: [27.5C]
使用RT-Thread的RTC框架，RTC设备注册名称为“rtc”，注意需先屏蔽芯片内置RTC驱动。
【1】pcf8563匹配RT-Thread驱动
【2】RT-Thread DS3231驱动软件包
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