Anyone know of a programmatic way (as in within C or Go code) to

Electronics
, ,
1

Anyone know of a programmatic way (as in within C or Go code) to apply a device tree overlay, i.e., “echo cape-bone-iio > /sys/devices/bone_capemgr.*/slots” (which works fine in the shell)? I’ve tried pipes and file copies, etc. but nothing seems to be working…

2

Here’s my code:

package bbbdevtreeovly

import (
// “io”
“bytes”
“fmt”
“io/ioutil”
“log”
“os”
“os/exec”
“strings”
“path/filepath”
)

const (
slotsDir string = /sys/devices/ // Find BBB’s slots
)

func Load_dto(dtoFileName string, dtoFilePath string) (err error) {

log.SetPrefix(`BBB Device Tree Overlay: `)

slotFiles := make([]os.FileInfo, 100)

slotFiles, err = ioutil.ReadDir(slotsDir)

var i int

for i = 0; i < len(slotFiles); i++ {
	//log.Println(slotFiles[i].Name())
	found, _ := filepath.Match(`bone_capemgr.*`, slotFiles[i].Name())
	if found {
		break
	}
}

slotsLoc := filepath.Join(slotsDir, slotFiles[i].Name(), `slots`)

log.Println("DTO File: ", dtoFileName, "\n")

slots, err := os.Open(slotsLoc)
if err != nil {
	log.Println(err)
	return err
}
defer slots.Close()

log.Println("Slots location: ", slots.Name(), "\n")

cmd := exec.Command(slotsLoc)

cmd.Stdin = strings.NewReader(dtoFileName)

var out bytes.Buffer
cmd.Stdout = &out

// cmd.StdinPipe(dtoFile)

err = cmd.Run()
if err != nil {
	log.Println(err)
	return err
}

/*
	io.Copy(slots, dtoFile)
	if err != nil {
		log.Println(err)
		return err
	}
*/

fmt.Println(out.String())

return nil

}

3

I get “permission denied”… See below…

root@beaglebone:~#./fmserve
BBB Device Tree Overlay: 2013/12/01 17:08:47 DTO File: cape-bone-iio

BBB Device Tree Overlay: 2013/12/01 17:08:47 Slots location: /sys/devices/bone_capemgr.9/slots

BBB Device Tree Overlay: 2013/12/01 17:08:47 exec: “/sys/devices/bone_capemgr.9/slots”: permission denied
panic: exec: “/sys/devices/bone_capemgr.9/slots”: permission denied

goroutine 1 [running]:
main.main()
/home/dad/go/src/davidsonff/fmserve/fmserve.go:16 +0x94

goroutine 2 [runnable]:

4

Based on the error message it looks like you are trying to run “/sys/devices/bone_capemgr.9/slots” as an executable program.

5

@Johan_Myreen Yes, I suspect, but I’ve also tried a programatic file copy and pipe to no effect. $SLOTS is not just a file, right? Is there a better explanation of what this is somewhere?

6

@MirandaSoft I saw this, thanks! I am trying to figure out how to do this from Go, actually, rather than a shell script. Perhaps it is not possible or I have simply not exploited all of the file methods yet…

7

@Frank_Davidson If you are trying to achieve the equivalent of the “echo” command you should not try to cmd.Run() the target file, just write to it. I.e. something like

slots,err := os.Open(slotsLoc)
slots.Write(thestring)

8

OK, tried writing out directly, still “Permission Denied”…

Here’s the code:

package bbbdevtreeovly

import (
// “io”
// “bytes”
// “fmt”
“io/ioutil”
“log”
“os”
// “os/exec”
// “strings”
“path/filepath”
)

const (
slotsDir string = /sys/devices/ // Find BBB’s slots
)

func Load_dto(dtoFileName string, dtoFilePath string) (err error) {

log.SetPrefix(`BBB Device Tree Overlay: `)

slotFiles := make([]os.FileInfo, 100)

slotFiles, err = ioutil.ReadDir(slotsDir)

var i int

for i = 0; i < len(slotFiles); i++ {
	found, _ := filepath.Match(`bone_capemgr.*`, slotFiles[i].Name())
	if found {
		break
	}
}

slotsLoc := filepath.Join(slotsDir, slotFiles[i].Name(), `slots`)

log.Println("DTO File: ", dtoFileName, "\n")

slots, err := os.Open(slotsLoc)
if err != nil {
	log.Println(err)
	return err
}
defer slots.Close()

log.Println("Slots location: ", slots.Name(), "\n")

slots.Write([]byte(dtoFileName))

return nil

}

Here’s the output:

root@beaglebone:~#./fmserve
BBB Device Tree Overlay: 2013/12/14 19:31:35 DTO File: cape-bone-iio

BBB Device Tree Overlay: 2013/12/14 19:31:35 Slots location: /sys/devices/bone_capemgr.9/slots

BBB Device Tree Overlay: 2013/12/14 19:31:35 exec: “/sys/devices/bone_capemgr.9/slots”: permission denied
panic: exec: “/sys/devices/bone_capemgr.9/slots”: permission denied

goroutine 1 [running]:
main.main()
/home/dad/go/src/davidsonff/fmserve/fmserve.go:16 +0x94
root@beaglebone:~#

Any ideas are welcome!

9

Are you sure you are running this version of the program, and not some older one? The output is identical, except for the timestamps.

10

OK. That was a problem! Now I’m not getting the “permissions denied” error, but it is still not loading the device tree overlay…

Here is the code:

package bbbdevtreeovly

import (
// “io”
// “bytes”
// “fmt”
“io/ioutil”
“log”
“os”
// “os/exec”
// “strings”
“path/filepath”
)

const (
slotsDir string = /sys/devices/ // Find BBB’s slots
)

func Load_dto(dtoFileName string, dtoFilePath string) (err error) {

log.SetPrefix(`BBB Device Tree Overlay: `)

slotFiles := make([]os.FileInfo, 100)

slotFiles, err = ioutil.ReadDir(slotsDir)

var i int

for i = 0; i < len(slotFiles); i++ {
	found, _ := filepath.Match(`bone_capemgr.*`, slotFiles[i].Name())
	if found {
		break
	}
}

log.Println("This is the new program...", "\n")

slotsLoc := filepath.Join(slotsDir, slotFiles[i].Name(), `slots`)

log.Println("DTO File: ", dtoFileName, "\n")

slots, err := os.Open(slotsLoc)
if err != nil {
	log.Println(err)
	return err
}
defer slots.Close()

log.Println("Slots location: ", slots.Name(), "\n")

slots.Write([]byte(dtoFileName))

return nil

}

11

Here is the output:

root@beaglebone:~#./fmserve
BBB Device Tree Overlay: 2013/12/15 16:18:59 This is the new program…

BBB Device Tree Overlay: 2013/12/15 16:18:59 DTO File: cape-bone-iio

BBB Device Tree Overlay: 2013/12/15 16:18:59 Slots location: /sys/devices/bone_capemgr.9/slots

Success!
root@beaglebone:~# cat /sys/devices/bone_capemgr.8/slots
cat: /sys/devices/bone_capemgr.8/slots: No such file or directory
root@beaglebone:~# cat /sys/devices/bone_capemgr.9/slots
0: 54:PF—
1: 55:PF—
2: 56:PF—
3: 57:PF—
4: ff:P-O-L Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G
5: ff:P-O-L Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI
root@beaglebone:~#