USB Gadget

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Revision as of 11:27, 3 March 2011 by JeremieS (Talk | contribs) (To emulate a serial link)

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Instructions on how to use the USB device (or OTG) port of your Armadeus board to communicate with your PC; ie see your board from your PC like an USB device.


You can connect your APF board to your PC using its USB Device port (APF9328DevFull), a modified USB host port (APF27Dev), or an USB OTG port (APF27 PPS), and it can be "enumerated" as most common USB devices (depending on the type of communication you want to use):

  • serial device
  • net device
  • mass storage device

Hardware/software specifics for the APF27dev and APF27 PPS boards

At first, an USB A male / A male cable has to be used like this one:

Do not use USB cable with integrated ferrite bead !!

The APF27dev board is equipped with two USB host ports. Only the high speed Host port (top connector) can be configured as an USB Device.

In order to activate the device mode, a new parameter has to be added to the U-Boot console variable:

BIOS> setenv console console=ttySMX0,115200 otg_mode=device
BIOS> saveenv
BIOS> boot

Your port will now work as an USB device.



  • The drivers are now installed by default (since armadeus-3.0)
  • you should have following modules in your kernel source tree:
drivers/usb/gadget/gadgetfs.ko        For test
drivers/usb/gadget/g_ether.ko         Ethernet emulation on USB
drivers/usb/gadget/g_file_storage.ko  Mass storage
drivers/usb/gadget/g_serial.ko        Serial emulation on USB
drivers/usb/gadget/g_zero.ko          For test


To emulate a mass storage device:

  • create or get a "backing storage file" (for example)
  • copy this file (uncompressed) in the /tmp directory of your board (here my Host PC has as IP @):
 # tftp -g -r backing_file.gz -l /tmp/backing_file.gz
 # gunzip /tmp/backing_file.gz
  • load g_file_storage module:
 # modprobe g_file_storage file=/tmp/backing_file
 g_file_storage gadget: File-backed Storage Gadget, version: 28 November 2005
 g_file_storage gadget: Number of LUNs=1
 g_file_storage gadget-lun0: ro=0, file: /tmp/backing_file
  • connect target's USB cable to your PC and,

On your Linux Host:

  • If you have a recent Linux distribution, your device should be automatically mounted. Otherwise:
    • as root, launch dmesg and find the /dev/sdaX device assigned to your board:
... usb 1-1.4: new full speed USB device using uhci_hcd and address 7
... usb 1-1.4: configuration #1 chosen from 1 choice
... scsi1 : SCSI emulation for USB Mass Storage devices
...    Vendor: Linux     Model: File-Stor Gadget  Rev: 0314
...    Type:   Direct-Access                      ANSI SCSI revision: 02
...  SCSI device sda: 8192 512-byte hdwr sectors (4 MB)
...  sda: Write Protect is off
...  SCSI device sda: 8192 512-byte hdwr sectors (4 MB)
...  sda: Write Protect is off
...   sda: sda1
...  sd 1:0:0:0: Attached scsi disk sda
...  sd 1:0:0:0: Attached scsi generic sg0 type 0
    • then mount the device and enjoy file sharing:
 $ sudo mount /dev/sda1 /mnt/tmp
 $ cd /mnt/tmp
 $ showimage /mnt/tmp/test.jpg

To emulate a serial link

  • On your Host PC (if usbserial module is not already loaded):
 $ sudo modprobe usbserial vendor=0x0525 product=0xA4A6

or you can automate it by modifying /etc/modprobe.d/options file (Tested on *Ubuntu):

 $ sudo vim /etc/modprobe.d/options
  options usbserial vendor=0x0525 product=0xA4A6
  • on your APF:
 # modprobe g_serial
 g_serial gadget: Gadget Serial v2.4
 g_serial gadget: g_serial ready
 fsl-usb2-udc: bind to driver g_serial
 g_serial gadget: high speed config #2: CDC ACM config

 # mknod /dev/ttyGS0 c 249 0   (if not created)
  • then connect the USB cable between your PC and your APF and you should see on your Host:
 $ tail -f /var/log/messages
 Sep 27 10:06:38 ...  usb 2-1.3: new high speed USB device using ehci_hcd and address 14
 Sep 27 10:06:38 ...  usb 2-1.3: configuration #2 chosen from 1 choice
 Sep 27 10:06:38 ...  cdc_acm 2-1.3:2.0: ttyACM0: USB ACM device
 Sep 27 10:06:38 ...  usbcore: registered new interface driver cdc_acm
 Sep 27 10:06:38 ...  cdc_acm: v0.26:USB Abstract Control Model driver for USB modems and ISDN adapters
  • you should now be able to send/receive data through /dev/ttyACM0 (PC) and /dev/ttyGS0 (APF):
 # cat /dev/ttyGS0
 [armadeus]$ echo "COUCOU" > /dev/ttyACM0

To emulate an Ethernet link

  • On your Target:
 # modprobe g_ether
 ether gadget: using random self ethernet address
 ether gadget: using random host ethernet address
 usb0: Ethernet Gadget, version: May Day 2005
 usb0: using imx_udc, OUT ep2out-bulk IN ep1in-bulk STATUS ep4in-int
 usb0: MAC be:df:31:95:16:e0
 usb0: HOST MAC 3e:86:1e:94:eb:84
 usb0: RNDIS ready

Now an IP address has to be assigned to the USB0 ethernet port

 # ifconfig usb0

  • On your PC:
    • On Linux systems:
      $ sudo modprobe cdc_ether
    • On Windows systems:
      When the target is detected, you will be asked to give the right driver.
      You will find it here: APF27 PPS Windrivers.