RTC

• Overview

  • Available APIs

• Usage Guidelines

  • How to Use
  • Creating an RTC Device Handle
  • Releasing the RTC Device Handle
  • Registering RtcAlarmCallback
  • Performing RTC-related Operations

• Usage Example

Overview

The real-time clock (RTC) driver provides precise real time for the operating system (OS). If the OS is powered off, the RTC driver continues to keep track of the system time using an external battery.

Available APIs

Table 1 APIs provided by the RTC driver

NOTE: All functions provided in this document can be called only in kernel mode.

Usage Guidelines

How to Use

During the OS startup, the HDF loads the RTC driver based on the configuration file. The RTC driver detects the RTC component and initializes the driver.

Figure 1 illustrates the process of using an RTC device.

Figure 1 Process of using an RTC device

Creating an RTC Device Handle

After the RTC driver is loaded, you can use the API provided by the HDF and call APIs of the RTC driver.

NOTE: Currently, only one RTC device is supported in the OS.

DevHandle RtcOpen(void);

Table 2 Description of RtcOpen

DevHandle  handle = NULL;

/* Obtain the RTC device handle. */
handle = RtcOpen();
if (handle  == NULL) {
    /* Process the error. */
}

Releasing the RTC Device Handle

You can call the following function to release the RTC device handle, thereby releasing resources of the device:

void RtcClose(DevHandle handle);

Table 3 Description of RtcClose

/* Release the RTC device handle. */
RtcClose(handle);

Registering RtcAlarmCallback

After the OS is started, call the following function to register RtcAlarmCallback, which will be invoked when an alarm is generated at the specified time:

int32_t RtcRegisterAlarmCallback(DevHandle handle, enum RtcAlarmIndex alarmIndex, RtcAlarmCallback cb);

Table 4 Description of RtcRegisterAlarmCallback

The following is an example of registering RtcAlarmCallback for processing alarm RTC_ALARM_INDEX_A:

/* Register an RTC alarm callback. */
int32_t RtcAlarmACallback(enum RtcAlarmIndex alarmIndex)
{
    if (alarmIndex == RTC_ALARM_INDEX_A) {
        /* Process alarm A. */
    } else if (alarmIndex == RTC_ALARM_INDEX_B) {
        /* Process alarm B. */
    } else {
        /* Process the error. */
    }
    return 0;
}
int32_t ret;
/* Register RtcAlarmCallback for alarm A. */
ret = RtcRegisterAlarmCallback(handle, RTC_ALARM_INDEX_A, RtcAlarmACallback);
if (ret != 0) {
    /* Process the error. */
}

Performing RTC-related Operations

• Reading RTC time

Call the following function to read time information from the RTC driver, including the year, month, the day of the week, day, hour, minute, second, and millisecond:

int32_t RtcReadTime(DevHandle handle, struct RtcTime *time);

Table 5 Description of RtcReadTime

int32_t ret;
struct RtcTime tm;

/* Read time information from the RTC driver. */
ret = RtcReadTime(handle, &tm);
if (ret != 0) {
    /* Process the error. */
}

• Setting RTC time

Call the following function to set the RTC time:

int32_t RtcWriteTime(DevHandle handle, struct RtcTime *time);

Table 6 Description of RtcWriteTime

NOTE: The RTC start time is 1970/01/01 Thursday 00:00:00 (UTC). The maximum value of year must be set based on the requirements specified in the product manual of the in-use component. You do not need to configure the day of the week.

int32_t ret;
struct RtcTime tm;

/* Set the RTC time to UTC 2020/01/01 00:59:00 .000. */
tm.year = 2020;
tm.month = 01;
tm.day = 01;
tm.hour= 00;
tm.minute = 59;
tm.second = 00;
tm.millisecond = 0;
/* Write the RTC time information. */
ret = RtcWriteTime(handle, &tm);
if (ret != 0) {
    /* Process the error. */
}

• Reading the RTC alarm time

Call the following function to read the alarm time:

int32_t RtcReadAlarm(DevHandle handle, enum RtcAlarmIndex alarmIndex, struct RtcTime *time);

Table 7 Description of RtcReadAlarm

int32_t ret;
struct RtcTime alarmTime;

/* Read the RTC alarm time information of alarm RTC_ALARM_INDEX_A. */
ret = RtcReadAlarm(handle, RTC_ALARM_INDEX_A, &alarmTime);
if (ret != 0) {
    /* Process the error. */
}

• Setting RTC alarm time

Call the following function to set the RTC alarm time based on the alarm index:

int32_t RtcWriteAlarm(DevHandle handle, enum RtcAlarmIndex alarmIndex, struct RtcTime *time);

Table 8 Description of RtcWriteAlarm

NOTE: The RTC start time is 1970/01/01 Thursday 00:00:00 (UTC). The maximum value of year must be set based on the requirements specified in the product manual of the in-use component. You do not need to configure the day of the week.

int32_t ret;
struct RtcTime alarmTime;

/* Set the RTC alarm time to 2020/01/01 00:59:59 .000. */
alarmTime.year = 2020;
alarmTime.month = 01;
alarmTime.day = 01;
alarmTime.hour = 00;
alarmTime.minute = 59;
alarmTime.second = 59;
alarmTime.millisecond = 0;
/* Set the alarm time of alarm RTC_ALARM_INDEX_A. */
ret = RtcWriteAlarm(handle, RTC_ALARM_INDEX_A, &alarmTime);
if (ret != 0) {
    /* Process the error. */
}

• Enabling or disabling alarm interrupts

Before performing alarm operations, use the following function to enable alarm interrupts, so that RtcAlarmCallback will be called when the alarm is not generated upon a timeout:

int32_t RtcAlarmInterruptEnable(DevHandle handle, enum RtcAlarmIndex alarmIndex, uint8_t enable);

Table 9 Description of RtcAlarmInterruptEnable

int32_t ret;

/* Enable the RTC alarm interrupts. */
ret = RtcAlarmInterruptEnable(handle, RTC_ALARM_INDEX_A, 1);
if (ret != 0) {
    /* Process the error. */
}

• Reading RTC external frequency

Call the following function to read the frequency of the external crystal oscillator connected to the RTC driver:

int32_t RtcGetFreq(DevHandle handle, uint32_t *freq);

Table 10 Description of RtcGetFreq

int32_t ret;
uint32_t freq = 0;

/* Read frequency of the external crystal oscillator connected to the RTC driver */
ret = RtcGetFreq(handle, &freq);
if (ret != 0) {
    /* Process the error. */
}

• Setting the frequency of the external crystal oscillator connected to the RTC driver

Call the following function to set the frequency of the external crystal oscillator connected to the RTC driver:

int32_t RtcSetFreq(DevHandle handle, uint32_t freq);

Table 11 Description of RtcSetFreq

int32_t ret;
uint32_t freq = 32768; /* 32768 Hz */

/* Set the frequency of the external crystal oscillator. Note that the frequency must be configured in accordance with the requirements specified in the product manual of the in-use component. */
ret = RtcSetFreq(handle, freq);
if (ret != 0) {
    /* Process the error. */
}

• Resetting the RTC driver

Call the following function to perform a reset on the RTC driver (after the reset, the registers are restored to the default values):

int32_t RtcReset(DevHandle handle);

Table 12 Description of RtcReset

int32_t ret;

/* Reset the RTC driver. After the reset, the configuration registers are restored to the default values. */
ret = RtcReset(handle);
if (ret != 0) {
    /* Process the error. */
}

• Reading the configuration of a custom RTC register

Call the following function to read the configuration of a custom RTC register based on the register index (one index corresponds to one byte of the configuration value):

int32_t RtcReadReg(DevHandle handle, uint8_t usrDefIndex, uint8_t *value);

Table 13 Description of RtcReadReg

int32_t ret;
uint8_t usrDefIndex = 0; /* Define index 0 for the first custom register. */
uint8_t value = 0;

/* Read the configuration of a custom RTC register based on the register index. One index corresponds to one byte of the configuration value. */
ret = RtcReadReg(handle, usrDefIndex, &value);
if (ret != 0) {
    /* Process the error. */
}

• Setting the configuration of a custom RTC register

Call the following function to configure a register based on the specified register index (one index corresponds to one byte of the configuration value):

int32_t RtcWriteReg(DevHandle handle, uint8_t usrDefIndex, uint8_t value);

Table 14 Description of RtcWriteReg

int32_t ret;
uint8_t usrDefIndex = 0; /* Define index 0 for the first custom register. */
uint8_t value = 0x10;

/* Configure a register based on the specified register index. One index corresponds to one byte of the configuration value. */
ret = RtcWriteReg(handle, usrDefIndex, value);
if (ret != 0) {
    /* Process the error. */
}

Usage Example

This section describes the process of using RTC APIs:

1. During the OS startup, the HDF identifies the RTC component in the system.
2. The HDF initializes and creates the RTC device.
3. You can perform operations on the RTC device by calling different APIs.
4. Call the RtcClose function to release the device handle and device resources.

Example:

#include "rtc_if.h"
int32_t RtcAlarmACallback(enum RtcAlarmIndex alarmIndex)
{
    if (alarmIndex == RTC_ALARM_INDEX_A) {
        /* Process alarm A. */
        printf("RTC Alarm A callback function\n\r");
    } else if (alarmIndex == RTC_ALARM_INDEX_B) {
        /* Process alarm B. */
        printf("RTC Alarm B callback function\n\r");
    } else {
        /* Process the error. */
    }
    return 0;
}

void RtcTestSample(void)
{
    int32_t ret;
    struct RtcTime tm;
    struct RtcTime alarmTime;
    uint32_t freq;
    DevHandle handle = NULL;

    /* Obtain the RTC device handle. */
    handle = RtcOpen();
    if (handle == NULL) {
        /* Process the error. */
    }
    /* Register RtcAlarmCallback for alarm A. */
    ret = RtcRegisterAlarmCallback(handle, RTC_ALARM_INDEX_A, RtcAlarmACallback);
    if (ret != 0) {
        /* Process the error. */
    }
    /* Set the RTC external crystal frequency. Note that the frequency must be configured in accordance with the requirements specified in the product manual of the in-use component. */
    freq = 32768; /* 32768 Hz */
    ret = RtcSetFreq(handle, freq);
    if (ret != 0) {
        /* Process the error. */
    }
    /* Enable the RTC alarm interrupts. */
    ret = RtcAlarmInterruptEnable(handle, RTC_ALARM_INDEX_A, 1);
    if (ret != 0) {
        /* Process the error. */
    }
    /* Set the RTC time to 2020/01/01 00:00:10 .990. */
    tm.year = 2020;
    tm.month = 01;
    tm.day = 01;
    tm.hour= 0;
    tm.minute = 0;
    tm.second = 10;
    tm.millisecond = 990;
    /* Write the RTC time information. */
    ret = RtcWriteTime(handle, &tm);
    if (ret != 0) {
        /* Process the error. */
    }
    /* Set the RTC alarm time to 2020/01/01 00:00:30 .100. */
    alarmTime.year = 2020;
    alarmTime.month = 01;
    alarmTime.day = 01;
    alarmTime.hour = 0;
    alarmTime.minute = 0;
    alarmTime.second = 30;
    alarmTime.millisecond = 100;
    /* Set the alarm time information for RTC_ALARM_INDEX_A. When the specified time is reached, "RTC Alarm A callback function" is printed. */
    ret = RtcWriteAlarm(handle, RTC_ALARM_INDEX_A, &alarmTime);
    if (ret != 0) {
        /* Process the error. */
    }

    /* Read the RTC real time. */
    ret = RtcReadTime(handle, &tm);
    if (ret != 0) {
        /* Process the error. */
    }
    sleep(5)
    printf("RTC read time:\n\r");
    printf("year-month-date-weekday hour:minute:second .millisecond %04u-%02u-%02u-%u %02u:%02u:%02u .%03u",
        tm.year, tm.month, tm.day, tm.weekday, tm.hour, tm.minute, tm.second, tm.millisecond);
    /* Release the RTC device handle. */
    RtcClose(handle);
}