Php Serial Port Communication Linux Kernel
I am attempting to connect to a serial device from a Android tablet, via USB-Serial Converter. In order to interface with this particular serial device, a linux library must be used as an interface. This library takes an integer as an argument, and tries to connect to the device at the following location: /dev/ttySx, where x is the arguement. If 2 is provided to the library, it will look for the device at /dev/ttyS2. When I connect the device to Ubuntu, there's is one simple extra step for this device to work with the USB-Serial convert. The converter is exposed at the location /dev/ttyUSB1.
I just need to create a simple soft-link with the serial port pattern (etc 'ln -s /dev/ttyUSV1 /dev/ttyS99'). It works perfectly. Now the problem arises for Android. The converter is seen at /dev/bus/usb/01/01. I never seen this convention in other project.
The question is how can I direct the I/O from /dev/ttySX to /dev/bus/usb/01/01. Quote: Originally Posted by ehpaul I am attempting to connect to a serial device from a Android tablet, via USB-Serial Converter. In order to interface with this particular serial device, a linux library must be used as an interface. This library takes an integer as an argument, and tries to connect to the device at the following location: /dev/ttySx, where x is the arguement. If 2 is provided to the library, it will look for the device at /dev/ttyS2. When I connect the device to Ubuntu, there's is one simple extra step for this device to work with the USB-Serial convert. The converter is exposed at the location /dev/ttyUSB1.
I just need to create a simple soft-link with the serial port pattern (etc 'ln -s /dev/ttyUSV1 /dev/ttyS99'). It works perfectly. Now the problem arises for Android. The converter is seen at /dev/bus/usb/01/01.
I never seen this convention in other project. The question is how can I direct the I/O from /dev/ttySX to /dev/bus/usb/01/01.
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Which android device are you using and with which kernel and android build? In my case I am using kernel 3.0.+ with CM9 on a Kindle Fire and I do see the /dev/ttyUSBx getting created along with the /dev/bus/01/01. It has been a month since I tried it but I was able to see the problem you see and here is what I remember. When you plug the serial convertor both /dev get created but since the Android USB support only uses /dev/bus/usb/01/01, the kernel in order to save power 'unmounts' the unused /dev/ttyUSBx after a certain time period.
You can try using dmesg to see if that is happening in your case also. There is a kernel build flag that tells the kernel not to 'unmount' it but I dont remember it off-hand.
Best would be to use the Android USB support to talk to your device instead of the linux library if you can. Quote: Originally Posted by pankaj013 Which android device are you using and with which kernel and android build? In my case I am using kernel 3.0.+ with CM9 on a Kindle Fire and I do see the /dev/ttyUSBx getting created along with the /dev/bus/01/01. It has been a month since I tried it but I was able to see the problem you see and here is what I remember. When you plug the serial convertor both /dev get created but since the Android USB support only uses /dev/bus/usb/01/01, the kernel in order to save power 'unmounts' the unused /dev/ttyUSBx after a certain time period. You can try using dmesg to see if that is happening in your case also.
There is a kernel build flag that tells the kernel not to 'unmount' it but I dont remember it off-hand. Best would be to use the Android USB support to talk to your device instead of the linux library if you can. This is from a question on stackoverflow titled 'Android USB host and hidden devices' (sorry, i can't add external URLs yet). It worked like a charm on a micromax A120 canvas 2 phone (kitkat 4.4.2). Now i can control my Arduino! I used busybox tools to do all the command line work (otherwise chmod wouldn't work). My steps (perhaps some were not required): (0) install PDAnet drivers on my Windows 8 computer.
(1) root the phone using Vroot (now called iRoot). Very simple, only catch is that the su grant/deny page is partly in chinese, no big deal.
(2) install busybox and jackpal's Android-Terminal-Emulator available on github and the google play store (free). (3) open a terminal window and become the superuser: # su (4) the file system may be read-only, so you might have to remount it: # mount -o rw,remount -t yaffs2 / or # mount -o rw,remount -t rootfs / or # mount -o rw,remount -t rootfs rootfs /system (5) make default.prop read/write: chmod 666 /default.prop (6) edit /default.prop, make the following changes: ro.secure=0 ro.debuggable=1 persist.service.adb.enable=1.
Linux Serial Port Communication
And this is the real meat of it: (7) To enable USB host API support you should add a file named android.hardware.usb.host.xml and containing the following lines: into folder /system/etc/permissions in that folder find file named handheldcorehardware.xml or tabletcorehardware.xml and add into section. (8) Reboot your device. Usb host api should work.