// This program achieves LED blink on Raspberry Pi with Go lang.
// This is implemented with hard-coding and uses only main function.

package main

import (
        "fmt"
        "os"
        "time"
)

func main() {
        // Initialize GPIO25
        fmt.Println("Initialize GPIO25")
        fd, err := os.OpenFile("/sys/class/gpio/export", os.O_WRONLY|os.O_SYNC, 0666)
        if err != nil {
                fmt.Println("open /sys/class/gpio/export fails")
                fmt.Println(err)
                return
        }
        fmt.Fprint(fd, "25")
        fd.Close()

        // Check iinitialization result
        fmt.Println("Check initialization result")
        _, err = os.Stat("/sys/class/gpio/gpio25")
        if err != nil {
                fmt.Println("Export GPIO25 fails")
                fmt.Println(err)
        } else {
                fmt.Println("Export GPIO25 succeeds")
        }

        // Set direction to out
        fmt.Println("Set direction of GPIO25 to out")
        fd, err = os.OpenFile("/sys/class/gpio/gpio25/direction", os.O_WRONLY|os.O_SYNC, 0666)
        if err != nil {
                fmt.Println("open /sys/class/gpio/gpio25/direction fails")
                fmt.Println(err)
        }
        fmt.Fprint(fd, "out")
        fd.Close()

        // Start blink
        fmt.Println("Start blink")
        for i := 0; i < 20; i++ {
                fd, err := os.OpenFile("/sys/class/gpio/gpio25/value", os.O_WRONLY|os.O_SYNC, 0666)
                if err != nil {
                        fmt.Println("open /sys/class/gpio/gpio25/value fails")
                        fmt.Println(err)
                }
                if i%2 == 1 {
                        // Turn on LED
                        fmt.Fprint(fd, 1)
                } else {
                        // Turn off LED
                        fmt.Fprint(fd, 0)
                }
                fd.Close()
                time.Sleep(100 * time.Millisecond)
        }

        // End
        fmt.Println("Start finalizing")
        fd, err = os.OpenFile("/sys/class/gpio/gpio25/value", os.O_WRONLY|os.O_SYNC, 0666)
        if err != nil {
                fmt.Println("open /sys/class/gpio/gpio25/value fails")
                fmt.Println(err)
        }
        // Turn off LED
        fmt.Println("Turn off LED")
        fmt.Fprint(fd, 0)

        fd.Close()

        fd, err = os.OpenFile("/sys/class/gpio/unexport", os.O_WRONLY|os.O_SYNC, 0666)
        if err != nil {
                fmt.Println("open /sys/class/gpio/unexport fails")
                fmt.Println(err)
                return
        }
        fmt.Fprint(fd, "25")
        fd.Close()
        fmt.Println("End finalizing")

}

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