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embd/host/bbb/analogpin.go

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// Analog I/O support on the BBB.
package bbb
import (
"fmt"
"io/ioutil"
"os"
"strconv"
"strings"
"github.com/kidoman/embd"
)
type analogPin struct {
id string
n int
drv embd.GPIODriver
val *os.File
initialized bool
}
func newAnalogPin(pd *embd.PinDesc, drv embd.GPIODriver) embd.AnalogPin {
return &analogPin{id: pd.ID, n: pd.AnalogLogical, drv: drv}
}
func (p *analogPin) N() int {
return p.n
}
func (p *analogPin) init() error {
if p.initialized {
return nil
}
var err error
if err = p.ensureEnabled(); err != nil {
return err
}
if p.val, err = p.valueFile(); err != nil {
return err
}
p.initialized = true
return nil
}
func (p *analogPin) ensureEnabled() error {
return ensureFeatureEnabled("cape-bone-iio")
}
func (p *analogPin) valueFilePath() (string, error) {
pattern := fmt.Sprintf("/sys/devices/ocp.*/helper.*/AIN%v", p.n)
return embd.FindFirstMatchingFile(pattern)
}
func (p *analogPin) openFile(path string) (*os.File, error) {
return os.OpenFile(path, os.O_RDONLY, os.ModeExclusive)
}
func (p *analogPin) valueFile() (*os.File, error) {
path, err := p.valueFilePath()
if err != nil {
return nil, err
}
return p.openFile(path)
}
func (p *analogPin) Read() (int, error) {
if err := p.init(); err != nil {
return 0, err
}
p.val.Seek(0, 0)
bytes, err := ioutil.ReadAll(p.val)
if err != nil {
return 0, err
}
str := string(bytes)
str = strings.TrimSpace(str)
return strconv.Atoi(str)
}
func (p *analogPin) Close() error {
if err := p.drv.Unregister(p.id); err != nil {
return err
}
if !p.initialized {
return nil
}
if err := p.val.Close(); err != nil {
return err
}
p.initialized = false
return nil
}