Changes between Version 13 and Version 14 of linux/OTG

Timestamp:

01/15/2026 10:38:21 PM (2 hours ago)

Author:

Ryan Erbstoesser

Comment:

add otg example

linux/OTG

@@ -440 +440 @@
 }}}
 
+The ID pin on OTG to Host cable (provided in our dev-kits) is grounded where-as the pin is floating on an OTG to device cable. When the ID pin is grounded the USB host controller will enumerate on the bus (regardless of having an actual USB device plugged in) and you first should verify that you see this occur.
+
+ * Start out by enabling kernel messages to the console so we can see the enumeration occur
+{{{
+echo 8 > /proc/sys/kernel/printk
+}}}
+
+ * Now with no cable plugged into the OTG connector:
+{{{
+lsusb
+Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
+Bus 001 Device 002: ID 0424:2744 Microchip Technology, Inc. (formerly SMSC) Hub
+Bus 001 Device 003: ID 0424:2740 Microchip Technology, Inc. (formerly SMSC) Hub Controller
+^^^ the first device is the controller for USB1 which goes to the USB hub (not the front panel connector)
+^^^ there is only one 1d6b:0002 device enumerated which is USB1 as the USB2 root hub should not yet be enumerated
+}}}
+
+ * Now plug in the OTG to host cable (without anything plugged into the other end) and you should see the USB host controller enumerate because the ID pin gets grounded
+{{{
+[  152.460804] ci_hdrc ci_hdrc.0: EHCI Host Controller
+[  152.465742] ci_hdrc ci_hdrc.0: new USB bus registered, assigned bus number 2
+[  152.485200] ci_hdrc ci_hdrc.0: USB 2.0 started, EHCI 1.00
+[  152.490877] usb usb2: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 6.12
+[  152.499172] usb usb2: New USB device strings: Mfr=3, Product=2, SerialNumber=1
+[  152.500834] systemd-journald[147]: sd-device: Failed to chase symlinks in "/sys/dev/char/189:128".
+[  152.506424] usb usb2: Product: EHCI Host Controller
+[  152.515775] systemd-journald[147]: sd-device: Failed to chase symlinks in "/sys/dev/char/189:128".
+[  152.520279] usb usb2: Manufacturer: Linux 6.12.0-00037-g7a3ed01ed94e ehci_hcd
+[  152.520286] usb usb2: SerialNumber: ci_hdrc.0
+[  152.529855] systemd-journald[147]: sd-device: Failed to chase symlinks in "/sys/dev/char/189:128".
+[  152.537747] hub 2-0:1.0: USB hub found
+[  152.553610] hub 2-0:1.0: 1 port detected
+^^^ the controller enumerates
+^^^ if this does not occur then you have a faulty/incompatible OTG-to-Host cable that doesn't GND the ID pin or there is a fault with the Gateworks board
+}}}
+
+ * Run the lsusb command:
+{{{
+lsusb
+Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
+Bus 001 Device 002: ID 0424:2744 Microchip Technology, Inc. (formerly SMSC) Hub
+Bus 001 Device 003: ID 0424:2740 Microchip Technology, Inc. (formerly SMSC) Hub Controller
+Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
+^^^ now we have both 1d6b:0002 root hubs
+}}}
+
+ * Now, plug a USB device into the type-A socket on the OTG-to-Host cable and it should enumerate; here is a Gateworks JTAG adapter:
+{{{
+[  778.779644] usb 2-1: Manufacturer: Gateworks
+[  778.779651] usb 2-1: SerialNumber: GW16042-D4
+[  778.824160] usbcore: registered new interface driver usbserial_generic
+[  778.830994] usbserial: USB Serial support registered for generic
+[  778.849159] usbcore: registered new interface driver ftdi_sio
+[  778.855051] usbserial: USB Serial support registered for FTDI USB Serial Device
+[  778.862576] ftdi_sio 2-1:1.0: FTDI USB Serial Device converter detected
+[  778.869425] usb 2-1: Detected FT2232H
+[  778.873673] usb 2-1: FTDI USB Serial Device converter now attached to ttyUSB0
+[  778.881092] ftdi_sio 2-1:1.1: FTDI USB Serial Device converter detected
+[  778.887940] usb 2-1: Detected FT2232H
+[  778.892161] usb 2-1: FTDI USB Serial Device converter now attached to ttyUSB1
+^^^ if you see no device enumerate then we need to question of VBUS is getting enabled; you can check this with a voltmeter or use a device that has an LED on it indicating bus voltage such as a Gateworks JTAG adapter which has a green LED on it indicating vbus is present
+}}}
+
+ * Run the lsusb command:
+{{{
+lsusb
+Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
+Bus 001 Device 002: ID 0424:2744 Microchip Technology, Inc. (formerly SMSC) Hub
+Bus 001 Device 003: ID 0424:2740 Microchip Technology, Inc. (formerly SMSC) Hub Controller
+Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
+Bus 002 Device 002: ID 0403:6010 Future Technology Devices International, Ltd FT2232C/D/H Dual UART/FIFO IC
+}}}
 
 [=#device-mode]