Changes between Version 11 and Version 12 of linux/OTG

Timestamp:

06/13/2025 06:39:01 PM (4 days ago)

Author:

Tim Harvey

Comment:

added additional documentation for USB CDC ADM gadget

linux/OTG

@@ -98 +98 @@
 
 [=#g_serial]
-=== g_serial - Serial Device Gadget ===
+=== g_serial - Serial Device Gadget
 The Serial Gadget supports CDC-ACM and CDC-OBEX which can inter-operate with the MS-Windows hosts or with Linux hosts using the 'cdc-acm' driver to create a 'USB-to-Serial' connection.
 
+On the target a serial device will be created as {{{/dev/ttyGS0}}} (or the next avaialble ttyGS device).
+
+On a host device (ie PC) a USB CDC ACM device (VID:PID 0525:a4a7 by default) will appear and behave as a serial device. Module parameters can specify the VID, PID, device version, manufacturer string, product string, serialnumber and whether or not to use CDC ACM, CDC OBEX, and the number of ports to create.
+
+A Linux USB Host supports this with the {{{cdc_acm}}} driver which will create a {{{/dev/ttyACM0}}} device (or the next available ttyACM).
+
+To use the Windows ACM driver you must have the "linux-cdc-acm.inf"
+file which supports all recent versions: see ​https://www.kernel.org/doc/Documentation/usb/gadget_serial.txt
+
 Example:
  * on target device (Gateworks board with OTG controller):
@@ -106 +115 @@
 modprobe g_serial
 }}}
- * on host device (ie PC) a USB CDC ACM device (VID:PID 0525:a4a7 by default) will appear and behave as a serial device
- * module parameters can specify the VID, PID, device version, 
-manufacturer string, product string, serialnumber
- * module parameters can specify whether or not to use CDC ACM, CDC OBEX, and the number of ports to create
-
-Linux USB Host notes:
- * the cdc_acm driver will enumerate this device as '/dev/ttyACM<n>'
-
-Windows USB Host notes:
- * see ​https://www.kernel.org/doc/Documentation/usb/gadget_serial.txt
+
+You can allow logins via the {{{/dev/ttyGS0}}} device on the target by running a {{{getty}}} process. For example:
+ * Configure Ubuntu for console login:
+{{{#!bash
+# Add g_serial to modules.conf so that its loaded on bootup:
+echo g_serial >> /etc/modules-load.d/modules.conf
+# create a systemd service for ttyGS0 by enabling a getty instance
+sudo systemctl enable getty@ttyGS0.service
+# (optional) edit systemd to modify ExecStart if you want to add/edit params to the getty process
+sudo systemctl edit getty@ttyGS0.service
+# start the getty service
+sudo systemctl start getty@ttyGS0.serivce
+}}}
+  - if you wish the device to be available earlier in the boot you would have to configure it static via CONFIG_USB_G_SERIAL=y and add /dev/ttyGS0 to the console kernel cmdline parameter.
+
+If you want to use a USB ACM serial console in U-Boot see [https://trac.gateworks.com/wiki/uboot#USBCDCACMSerialGadget here].
 
 Reference:
  * ​https://www.kernel.org/doc/Documentation/usb/gadget_serial.txt
-
 
 [=#g_cdc]