国产risc-v微控制器读取DS3231
本帖最后由 dirtwillfly 于 2025-9-28 20:30 编辑第一部分：DS3231介绍
1.1 特性
DS3231 是一款 I2C 实时时钟 (RTC)，具有内置温度补偿晶体振荡器 (TCXO) 和低成本且异常精确的晶体。当模块的电源中断时，设备有电池输入并保持精确的时间。该器件的长期精度因包含晶体振荡器而得到提高。RTC 跟踪秒、分钟、小时、天、日期、月和年。对于少于 31 天的月份，月末日期会自动修改，包括闰年更正。时钟具有 AM/PM 指示，可在 24 小时或 12 小时模式下工作。包括两个可编程的时间警报，以及一个可编程的方波输出。I2C 双向总线用于串行传输地址和数据。
关键特性：
• 高精确时钟 ：具有+/-2ppm（百万分之二）的精度，从0°C到+40°C。
• 温度补偿 ：内置温度传感器，能够自动补偿时钟频率偏移。
• 集成备份电池 ：当主电源失效时，内置锂电池自动切换，保证时钟继续运行
1.2 参数
[*]0°C至+40°C范围内精度为±2ppm
[*]-40°C至+85°C范围内精度为±3.5ppm
[*]为连续计时提供电池备份输入
[*]工作温度范围
[*]商用级：0°C至+70°C
[*]工业级：-40°C至+85°C
[*]低功耗
[*]实时时钟产生秒、分、时、星期、日期、月和年计时，并提供有效期到2100年的闰年补偿
[*]两个日历闹钟
[*]可编程方波输出
[*]高速(400kHz) I²C接口
[*]工作在3.3V
[*]数字温度传感器输出：精度为±3°C
[*]老化修正寄存器
[*]/RST输出/按钮复位去抖输入
1.3 电路原理图
使用的模块：
与ds3231相关的原理图：
其中有一点要特别注意，因为原理图中VCC经过限流电阻和二极管连接到BAT，这是一个BAT的限流充电电路。所以这里的BAT电池必须使用可充电的CR2032。
第二部分：应用开发
2.1 硬件连接方式
使用的HPM5361开发板P1接口有两组I2C接口，这里使用I2C0接口，即PB03和PB02引脚。
https://bbs.21ic.com/data/attachment/forum/202507/27/204618f5qsg8tj7s7t85mi.png.thumb.jpg
这两个引脚，在开发板上已经有了10K的上拉电阻，使用的DS3231上也有上拉电阻，这里可以共存，不需要特殊处理。
https://bbs.21ic.com/data/attachment/forum/202507/27/204903dwvkdk9wzklt1wxv.png.thumb.jpg
2.2 驱动代码
#define DS3231_ARRD 0x68 /* slave address */
#define REG_SEC 0x00
#define REG_MIN 0x01
#define REG_HOUR 0x02
#define REG_DAY 0x03
#define REG_WEEK 0x04
#define REG_MON 0x05
#define REG_YEAR 0x06
#define REG_ALM1_SEC 0x07
#define REG_ALM1_MIN 0x08
#define REG_ALM1_HOUR 0x09
#define REG_ALM1_DAY_DATE 0x0A
#define REG_ALM2_MIN 0x0B
#define REG_ALM2_HOUR 0x0C
#define REG_ALM2_DAY_DATE 0x0D
#define REG_CONTROL 0x0E
#define REG_STATUS 0x0F
#define REG_AGING_OFFSET 0x10
#define REG_TEMP_MSB 0x11
#define REG_TEMP_LSB 0x12
#define DS3231_I2C_BUS "i2c0" /* i2c linked */
#define DS3231_DEVICE_NAME"rtc" /* register device name */
static struct rt_device ds3231_dev; /* ds3231 device */
static unsigned char bcd_to_hex(unsigned char data)
{
unsigned char temp;
temp = ((data>>4)*10 + (data&0x0f));
return temp;
}
static unsigned char hex_to_bcd(unsigned char data)
{
unsigned char temp;
temp = (((data/10)<<4) + (data%10));
return temp;
}
static rt_err_tds3231_read_reg(rt_device_t dev, rt_uint8_t reg,rt_uint8_t *data,rt_uint8_t data_size)
{
struct rt_i2c_msg msg;
struct rt_i2c_bus_device *i2c_bus = RT_NULL;
RT_ASSERT(dev != RT_NULL);
i2c_bus = (struct rt_i2c_bus_device*)dev->user_data;
msg.addr= DS3231_ARRD;
msg.flags = RT_I2C_WR;
msg.len = 1;
msg.buf = ®
msg.addr= DS3231_ARRD;
msg.flags = RT_I2C_RD;
msg.len = data_size;
msg.buf = data;
if(rt_i2c_transfer(i2c_bus, msg, 2) == 2)
{
return RT_EOK;
}
else
{
LOG_E("i2c bus read failed!\r\n");
return -RT_ERROR;
}
}
static rt_err_tds3231_write_reg(rt_device_t dev, rt_uint8_t reg, rt_uint8_t *data, rt_uint8_t data_size)
{
struct rt_i2c_msg msg;
struct rt_i2c_bus_device *i2c_bus = RT_NULL;
RT_ASSERT(dev != RT_NULL);
i2c_bus = (struct rt_i2c_bus_device*)dev->user_data;
msg.addr = DS3231_ARRD;
msg.flags = RT_I2C_WR;
msg.len = 1;
msg.buf = ®
msg.addr = DS3231_ARRD;
msg.flags = RT_I2C_WR | RT_I2C_NO_START;
msg.len = data_size;
msg.buf = data;
if(rt_i2c_transfer(i2c_bus, msg, 2) == 2)
{
return RT_EOK;
}
else
{
LOG_E("i2c bus write failed!\r\n");
return -RT_ERROR;
}
}
static rt_err_t rt_ds3231_open(rt_device_t dev, rt_uint16_t flag)
{
if (dev->rx_indicate != RT_NULL)
{
/* open interrupt */
}
return RT_EOK;
}
static rt_size_t rt_ds3231_read(rt_device_t dev, rt_off_t pos, void *buffer, rt_size_t size)
{
return RT_EOK;
}
static rt_err_t rt_ds3231_control(rt_device_t dev, int cmd, void *args)
{
rt_err_t ret = RT_EOK;
time_t *time;
struct tm time_temp;
rt_uint8_tbuff;
RT_ASSERT(dev != RT_NULL);
rt_memset(&time_temp, 0, sizeof(struct tm));
switch (cmd)
{
/* read time */
case RT_DEVICE_CTRL_RTC_GET_TIME:
time = (time_t *)args;
ret = ds3231_read_reg(dev, REG_SEC,buff,7);
if(ret == RT_EOK)
{
time_temp.tm_year= bcd_to_hex(buff) + 2000 - 1900;
time_temp.tm_mon = bcd_to_hex(buff&0x7f) - 1;
time_temp.tm_mday= bcd_to_hex(buff);
time_temp.tm_hour= bcd_to_hex(buff);
time_temp.tm_min = bcd_to_hex(buff);
time_temp.tm_sec = bcd_to_hex(buff);
*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 = hex_to_bcd(time_new->tm_year + 1900 - 2000);
buff = hex_to_bcd(time_new->tm_mon + 1);
buff = hex_to_bcd(time_new->tm_mday);
buff = hex_to_bcd(time_new->tm_wday+1);
buff = hex_to_bcd(time_new->tm_hour);
buff = hex_to_bcd(time_new->tm_min);
buff = hex_to_bcd(time_new->tm_sec);
ret = ds3231_write_reg(dev, REG_SEC, buff, 7);
}
break;
#ifdef RT_USING_ALARM
/* get alarm time */
case RT_DEVICE_CTRL_RTC_GET_ALARM:
{
struct rt_rtc_wkalarm *alm_time;
ret = ds3231_read_reg(dev, REG_ALM1_SEC, buff, 4);
if(ret == RT_EOK)
{
alm_time = (struct rt_rtc_wkalarm *)args;
alm_time->tm_hour= bcd_to_hex(buff);
alm_time->tm_min = bcd_to_hex(buff);
alm_time->tm_sec = bcd_to_hex(buff);
}
}
break;
/* set alarm time */
case RT_DEVICE_CTRL_RTC_SET_ALARM:
{
struct rt_rtc_wkalarm *alm_time;
alm_time = (struct rt_rtc_wkalarm *)args;
buff = 0x80; /* enable, alarm when hours, minutes, and seconds match */
buff = hex_to_bcd(alm_time->tm_hour);
buff = hex_to_bcd(alm_time->tm_min);
buff = hex_to_bcd(alm_time->tm_sec);
ret = ds3231_write_reg(dev, REG_ALM1_SEC, buff, 4);
}
break;
#endif
default:
break;
}
return ret;
}
float ds3231_get_temperature(void)
{
rt_int8_t buff;
float temp = 0.0f;
ds3231_read_reg(&ds3231_dev, REG_TEMP_MSB, (rt_uint8_t*)buff, 2);
if(buff&0x80)
{/* negative temperature */
temp = buff;
temp -= (buff>>6)*0.25;/* 0.25C resolution */
}
else
{/* positive temperature */
temp = buff;
temp += ((buff>>6)&0x03)*0.25;
}
return temp;
}
int rt_hw_ds3231_init(void)
{
struct rt_i2c_bus_device *i2c_device;
uint8_t data;
i2c_device = rt_i2c_bus_device_find(DS3231_I2C_BUS);
if (i2c_device == RT_NULL)
{
LOG_E("i2c bus device %s not found!\r\n", DS3231_I2C_BUS);
return -RT_ERROR;
}
/* register rtc device */
ds3231_dev.type = RT_Device_Class_RTC;
ds3231_dev.init = RT_NULL;
ds3231_dev.open = rt_ds3231_open;
ds3231_dev.close = RT_NULL;
ds3231_dev.read = rt_ds3231_read;
ds3231_dev.write = RT_NULL;
ds3231_dev.control = rt_ds3231_control;
ds3231_dev.user_data = (void*)i2c_device; /* save i2cbus */;
rt_device_register(&ds3231_dev, DS3231_DEVICE_NAME, RT_DEVICE_FLAG_RDWR);
/* init ds3231 */
data = 0x04; /* close clock out */
ds3231_write_reg(&ds3231_dev, REG_CONTROL, &data, 1);
LOG_D("the rtc of ds3231 init succeed!");
return 0;
}
//INIT_DEVICE_EXPORT(rt_hw_ds3231_init);
INIT_COMPONENT_EXPORT(rt_hw_ds3231_init);
#ifdef RT_USING_FINSH
#include <finsh.h>
void list_ds31_temp(void)
{
float temp = 0.0f;
temp = ds3231_get_temperature();
rt_kprintf("ds3231 temperature: [%d.%dC] \n", (int)temp, (int)(temp * 10) % 10);
}
FINSH_FUNCTION_EXPORT(list_ds31_temp, list ds3231 temperature.)
#endif /* RT_USING_FINSH */
2.3 效果验证
经过验证，可以从ds3231上读取到温度值，说明读取寄存器时正常的。但使用date命令回复的时间没有变化，说明rtthread的rtc框架和ds3231驱动间的衔接有问题。经过排查，发现rtthread的系统代码让先楫改的面目全非，不再支持外部rtc了。
解决方案，不使用rtc框架，直接读取DS3231的寄存器就可以解决。
备用
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