How to Test Code for Real-Time Clock (RTC) Linux Driver: Comprehensive Guide

Testing code for Real-Time Clock (RTC) Linux drivers is crucial for ensuring accurate timekeeping and system reliability. RTC drivers play a critical role in maintaining system time across reboots and during power loss. This guide provides a detailed approach to testing RTC Linux drivers, including tools, methods, and best practices to ensure your driver functions correctly.

Understanding RTC Linux Drivers

RTC Linux drivers manage the Real-Time Clock hardware, which maintains the current time even when the system is powered off. These drivers are essential for tasks such as scheduling tasks, logging events, and managing time-sensitive operations.

Why Testing RTC Drivers is Important

• Accuracy: Ensures that the RTC driver keeps accurate time.
• Reliability: Validates the driver’s functionality across different power states and system reboots.
• Compliance: Confirms that the driver adheres to Linux kernel standards and specifications.

1. Setting Up the Test Environment

Before testing, ensure you have a suitable environment:

• Linux System: Use a Linux distribution compatible with your RTC driver.
• Kernel Source: Ensure you have access to the kernel source code, as testing may require kernel modifications.
• RTC Hardware: A system with RTC hardware for real-time testing, or a virtual environment with RTC emulation.

2. Building and Installing the RTC Driver

If you’re working with a custom RTC driver, compile and install it:

make
sudo make install

Ensure the driver is loaded:

lsmod | grep rtc

3. Testing RTC Driver Functionality

Test the RTC driver using the following methods:

a. Kernel Command-Line Parameters

Check and configure RTC driver parameters via kernel command-line options. Use the dmesg command to view RTC driver messages:

dmesg | grep rtc

b. RTC Utilities

Use hwclock to interact with the RTC:

• Read the RTC Time:

   sudo hwclock --show

• Set the RTC Time:

   sudo hwclock --set --date="2024-08-21 12:34:56"

• Sync RTC with System Time:

   sudo hwclock --systohc

c. Writing Test Scripts

Develop scripts to automate RTC driver tests. Example script to verify RTC functionality:

#!/bin/bash

# Save the current system time
current_time=$(date +%s)

# Set the RTC to a specific time
sudo hwclock --set --date="2024-08-21 12:00:00"

# Read the RTC time and compare
rtc_time=$(sudo hwclock --show --utc | awk '{print $4}')

# Check if RTC time matches expected time
if [ "$rtc_time" = "12:00:00" ]; then
    echo "RTC Test Passed"
else
    echo "RTC Test Failed"
fi

# Restore the original system time
sudo hwclock --set --date="$(date -d @$current_time '+%Y-%m-%d %H:%M:%S')"

d. Checking Time Accuracy

Verify RTC accuracy by comparing RTC time against system time over an extended period. Use hwclock to read and compare times periodically.

4. Handling Common Issues

• Inaccurate Time: Verify RTC hardware and configuration settings.
• Driver Loading Problems: Check kernel logs for errors using dmesg and ensure driver modules are properly loaded.
• Power Loss Handling: Test RTC behavior across power cycles to ensure time is maintained correctly.

5. Automated Testing Tools

Leverage automated testing tools for comprehensive testing:

• LTP (Linux Test Project): Includes tests for various kernel subsystems, including RTC.
• Custom Test Suites: Develop custom test suites to cover specific RTC driver functionalities.

6. Best Practices

• Regular Testing: Implement continuous testing to catch issues early.
• Documentation: Maintain detailed documentation of test procedures and results.
• Kernel Updates: Keep your kernel and drivers updated to benefit from the latest fixes and improvements.

7. We can also write the C code as below to test the driver

 $ vim gettime.c 

/*
 * Test Code for Real Time Clock Driver
 *
 * Compile with:
 *      gcc -s -Wall -Wstrict-prototypes gettime.c -o gettime
 *
 * This binary is a part of RTC test suite.
 *
 * History:
 * Copyright (C) 1996, Paul Gortmaker. This version is based on Paul's
 *
 * XX-XX-XXXX   Texas Instruments       Initial version of the testcode
 * 12-09-2008   Ricardo Perez Olivares  Adding basic comments, variable
 *                                      names according to coding
 *                                      standars.
 *
 * Copyright (C) 2004-2009 Texas Instruments, Inc
 *
 * This package 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.
 *
 * THIS PACKAGE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 */
 
#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 <errno.h>
 
int main(int argc, char *argv[])
{
 
    int fd, retval;
    struct rtc_time rtc_tm;
 
    /* Creating a file descriptor for RTC */
    fd = open(argv[1], O_RDONLY);
    if (fd == -1) {
        perror("Requested device cannot be opened!");
        _exit(errno);
    }
 
    /* Reading Current RTC Date/Time */
    retval = ioctl(fd, RTC_RD_TIME, &rtc_tm);
    if (retval == -1) {
        perror("ioctl");
        _exit(errno);
    }
    fprintf(stdout, "\nCurrent RTC Date/Time: %d-%d-%d %02d:%02d:%02d\n\n",
        rtc_tm.tm_mday, rtc_tm.tm_mon + 1, rtc_tm.tm_year + 1900,
        rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);
    fflush(stdout);
    fflush(stdout);
    fflush(stdout);
    close(fd);
    return 0;
}

 $ gcc -s -Wall -Wstrict-prototypes gettime.c -o gettime 

 $ sudo ./gettime /dev/rtc 

Conclusion

Testing code for Real-Time Clock (RTC) Linux drivers is essential for ensuring that your driver performs reliably and accurately. By following the methods and best practices outlined in this guide, you can effectively validate your RTC driver’s functionality and maintain system integrity.