Go (Golang) module for using a hardware Real-Time Clock (RTC) device in Linux.

$ go get github.com/cleroux/rtc

rtc.NewTicker() and rtc.NewTimer() provide high-level interfaces inspired by Go's time.NewTicker() and time.NewTimer() with the obvious difference being that the rtc functions trigger directly from the RTC's hardware interrupts.

The following example creates a ticker that fires at 2 Hz.

ticker, err := rtc.NewTicker("/dev/rtc", 2)
if err != nil {
    panic(err)
}
defer ticker.Stop()

for tick := range ticker.C {
    fmt.Printf("Tick.  Frame:%d Time:%v Delta:%v Missed:%d\n", tick.Frame, tick.Time, tick.Delta, tick.Missed)
}

The following example sets an alarm for 5 seconds in the future and waits for the alarm to fire.

timer, err := rtc.NewTimer("/dev/rtc", time.Minute)
if err != nil {
    panic(err)
}
defer timer.Stop()

alarm := <-timer.C
fmt.Printf("Alarm.  Time:%v\n", alarm.Time)

If more flexible programming of the RTC is needed, rtc.NewRTC() instantiates an object that exposes all RTC functionality. The RTC device file is kept open until Close() is called.

c, err := rtc.NewRTC("/dev/rtc")
if err != nil {
  return err
}
defer c.Close()

t, err := c.Time()

Lastly, for convenience, static utility functions are also provided. These functions are ideal when just a single function or operation is necessary because they open and close the RTC device. For example, if reading the RTC's time as in the following example:

t, err := rtc.Time("/dev/rtc")
if err != nil {
  panic(err)
}
fmt.Printf("Current time: %v\n", t)

Since accessing the Real-Time Clock requires root privileges, tests must also run as root.

sudo make test

The go executable needs to be found in the root user's PATH. Edit /etc/sudoers with the visudo command and add the location of the go executable to secure_path.
For example:

`Defaults        secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin:/usr/local/go/bin"

Issues and Pull Requests welcome!

[1] The Linux kernel user's and administrator's guide: Real Time Clock (RTC) Drivers for Linux
[2] rtc - Linux manual page

See the LICENSE file for license rights and limitations (MIT).