Added support for PullUp / PullDown / PullOff

README.md

@@ -1,9 +1,9 @@
 go-rpio
 =======
 
-Native GPIO-Gophers for your Pi! 
+Native GPIO-Gophers for your Pi!
 
-go-rpio is a Go library for accessing [GPIO](http://elinux.org/Rpi_Low-level_peripherals)-pins 
+go-rpio is a Go library for accessing [GPIO](http://elinux.org/Rpi_Low-level_peripherals)-pins
 on the [Raspberry Pi](https://en.wikipedia.org/wiki/Raspberry_Pi).
 
 It requires no external c libraries such as
@@ -22,7 +22,7 @@ err := rpio.Open()
 ```
 
 Initialize a pin, run basic operations.
-Pin refers to the bcm2835 pin, not the physical pin on the raspberry pi header. Pin 10 here is exposed on the pin header as physical pin 19. 
+Pin refers to the bcm2835 pin, not the physical pin on the raspberry pi header. Pin 10 here is exposed on the pin header as physical pin 19.
 
 ```go
 pin := rpio.Pin(10)
@@ -39,6 +39,16 @@ pin.Mode(rpio.Output)   // Alternative syntax
 pin.Write(rpio.High)    // Alternative syntax
 ```
 
+Pull up/down/off can be set using:
+
+```go
+pin.PullUp()
+pin.PullDown()
+pin.PullOff()
+
+pin.Pull(rpio.PullUp)
+```
+
 Unmap memory when done
 
 ```go
@@ -53,11 +63,10 @@ Currently, it supports basic functionality such as:
 - Pin Direction (Input / Output)
 - Write (High / Low)
 - Read (High / Low)
+- Pull (Up / Down / Off)
 
 Would be nice to add in the future:
 - PWM
-- PullUp
-- PullDown
 - I2C
 - SPI
 - etc...

examples/pullup/pullup.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"fmt"
+	"github.com/stianeikeland/go-rpio"
+	"os"
+)
+
+var (
+	// Use mcu pin 22, corresponds to GPIO3 on the pi
+	pin = rpio.Pin(22)
+)
+
+func main() {
+	// Open and map memory to access gpio, check for errors
+	if err := rpio.Open(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	// Unmap gpio memory when done
+	defer rpio.Close()
+
+	// Pull up and read value
+	pin.PullUp()
+	fmt.Printf("PullUp: %d\n", pin.Read())
+
+	// Pull down and read value
+	pin.PullDown()
+	fmt.Printf("PullDown: %d\n", pin.Read())
+
+}

rpio.go

@@ -7,6 +7,7 @@ Supports simple operations such as:
 - Pin mode/direction (input/output)
 - Pin write (high/low)
 - Pin read (high/low)
+- Pull up/down/off
 
 Example of use:
 
@@ -59,12 +60,14 @@ import (
 	"reflect"
 	"sync"
 	"syscall"
+	"time"
 	"unsafe"
 )
 
 type Direction uint8
 type Pin uint8
 type State uint8
+type Pull uint8
 
 // Memory offsets for gpio, see the spec for more details
 const (
@@ -87,6 +90,13 @@ const (
 	High
 )
 
+// Pull Up / Down / Off
+const (
+	PullOff Pull = iota
+	PullDown
+	PullUp
+)
+
 // Arrays for 8 / 32 bit access to memory and a semaphore for write locking
 var (
 	memlock sync.Mutex
@@ -134,6 +144,26 @@ func (pin Pin) Read() State {
 	return ReadPin(pin)
 }
 
+// Set a given pull up/down mode
+func (pin Pin) Pull(pull Pull) {
+	PullMode(pin, pull)
+}
+
+// Pull up pin
+func (pin Pin) PullUp() {
+	PullMode(pin, PullUp)
+}
+
+// Pull down pin
+func (pin Pin) PullDown() {
+	PullMode(pin, PullDown)
+}
+
+// Disable pullup/down on pin
+func (pin Pin) PullOff() {
+	PullMode(pin, PullOff)
+}
+
 // WritePin sets the direction of a given pin (Input or Output)
 func PinMode(pin Pin, direction Direction) {
 
@@ -197,6 +227,36 @@ func TogglePin(pin Pin) {
 	}
 }
 
+func PullMode(pin Pin, pull Pull) {
+	// Pull up/down/off register has offset 38 / 39, pull is 37
+	pullClkReg := uint8(pin)/32 + 38
+	pullReg := 37
+	shift := (uint8(pin) % 32)
+
+	memlock.Lock()
+
+	switch pull {
+	case PullDown, PullUp:
+		mem[pullReg] = mem[pullReg]&^3 | uint32(pull)
+	case PullOff:
+		mem[pullReg] = mem[pullReg] &^ 3
+	}
+
+	// Wait for value to clock in, this is ugly, sorry :(
+	time.Sleep(time.Microsecond)
+
+	mem[pullClkReg] = 1 << shift
+
+	// Wait for value to clock in
+	time.Sleep(time.Microsecond)
+
+	mem[pullReg] = mem[pullReg] &^ 3
+	mem[pullClkReg] = 0
+
+	memlock.Unlock()
+
+}
+
 // Open and memory map GPIO memory range from /dev/mem .
 // Some reflection magic is used to convert it to a unsafe []uint32 pointer
 func Open() (err error) {