raspi_gpio_bcm2835_set_pull.go

package main

import (
	"os"
	"strconv"
	"syscall"
	"unsafe"
)

var mm []uint32

// https://git.io/JSLoq
var defaultPull = [54]byte{
	/* 00-08 UP   */ 2, 2, 2, 2, 2, 2, 2, 2, 2,
	/* 09-27 DOWN */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	/* 28-29 NONE */ 0, 0,
	/* 30-33 DOWN */ 1, 1, 1, 1,
	/* 34-36 UP   */ 2, 2, 2,
	/* 37-43 DOWN */ 1, 1, 1, 1, 1, 1, 1,
	/* 44-45 NONE */ 0, 0,
	/* 46-53 UP   */ 2, 2, 2, 2, 2, 2, 2, 2,
}

// https://git.io/JSLi3
//go:noinline
func sleep150cycles() uint32 {
	var out uint32
	for range [150]struct{}{} {
		out += mm[0]
	}
	return out
}

func main() {
	// https://git.io/JSLo2
	fd, err := syscall.Open("/dev/gpiomem", syscall.O_RDWR|syscall.O_SYNC|syscall.O_CLOEXEC, 0600)
	if err != nil {
		panic(err)
	}
	defer syscall.Close(fd)

	// https://git.io/JSLoP
	const l = 0x1000
	mb, err := syscall.Mmap(fd, 0, l, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
	if err != nil {
		panic(err)
	}
	defer syscall.Munmap(mb)
	mm = (*[l]uint32)(unsafe.Pointer(&mb[0]))[:] // this is what you came for

	args := os.Args[1:]
	if len(args) < 2 {
		panic("no enough arguments")
	}
	pin, _ := strconv.Atoi(args[0])
	pull, _ := strconv.Atoi(args[1])
	if pin < 0 || pin > 53 {
		panic("invalid pin given")
	}
	if pull < -1 || pull > 2 {
		panic("invalid pull given")
	}

	// https://git.io/JSLod
	const (
		GPPUD     = 0x0094 / 4
		GPPUDCLK0 = 0x0098 / 4
	)
	clkreg := GPPUDCLK0 + (pin / 32)
	clkbit := 1 << (pin % 32)
	if pull < 0 {
		pull = int(defaultPull[pin-1])
	}

	// https://git.io/JSLiD
	mm[GPPUD] = uint32(pull)
	sleep150cycles()
	mm[clkreg] = uint32(clkbit)
	sleep150cycles()
	// datasheet doesn't sleep here:
	mm[GPPUD] = 0
	mm[clkreg] = 0
}