Friday, September 23, 2016

BeagleBone to Android via USB Serial

As I mentioned in my last post, BeagleBone uses the Linux g_multi kernel module so that when you plug it into a PC, it appears to be a USB hub with USB-serial, USB-ethernet and USB storage devices attached.

In the other post I talk about how to plug a BeagleBone into an Android phone via USB and communicate between them using Ethernet.  Unfortunately it requires shutting off Wifi and cellular data.

So instead, I investigated communicating via USB serial instead of USB ethernet.  It should work out of the box, but none of the dozens of Android apps I tried could find the USB Serial device the BeagleBone provided.

Thus I used the same trick as before, replacing g_multi with a single-purpose device.  As in the last post, you'll have to comment out a big block of shell script in /opt/scripts/boot/

Then, instead of adding "modprobe g_cdc ${g_network}" and "usb0=enable" to explicitly load the USB Ethernet CDC driver, add:

modprobe g_serial

When you reboot, you won't be able to "ssh" from your PC anymore.  Instead, you'll only get /dev/ttyACM0, and you'll need to login using a terminal emulator like minicom or screen.

(As before, you may want to make these changes while booting from a microSD card so that you can just pop the card out if it doesn't work).

After verifying that I could get in from my workstation, I connected my phone to the BeagleBone with an OTG adapter (careful!  Not all of them work right), then used the "Android USB Serial Monitor Lite" to connect to the BeagleBone.  (Open the "three dots" menu and select "Open Device", then send a newline and you should get a login prompt).

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