I want to use alsa on a Beaglebone Black to send audio through usb audio out and receive it on my computer.
I have seen that there are some gadgets in a legacy folder in the kernel, and seen some tutorials on how to set up mass storage and network gadgets, but I am confused about what the state of audio gadgets is and what to compile and configure for this.
Can you explain the various components and configurations that need to go into place to make this happen, covering which kernel modules, drivers, kinds of scripts, and configurations that might be needed to do this?
You need to enable USB gadget subsystem in your Linux kernel for Beaglebone Black. Assuming of course that you have USB device controller and USB device connector on your Beaglebone. Here there are more information:
https://www.lynxbee.com/usb-audio-gadget-driver/
USB devices contains so called USB descriptors which tells USB host (PC) as a what device type it works. Audio gadget is one of the type of that descriptor that tells that this device (in this case BeagleBone) should be working as a audio device.
Related
I am learning to program a USB device (iBall 3.5g USB Dongle) using libusb.h header library.
Until now I am able to identify my device using the Vendor ID and also open the device for operation.
As a next step I would like to know the available commands (or the controls) for example : command to scan the surroundings for available GSM networks.
Obviously I will have to talk to the devices' firmware to extract the necessary information.
I tried to search for the technical datasheet for the 3g dongle, but couldn't find any.
The dongle is powered by a Qualcomm chip
Do you know any of the methods in which I can get the control commands for a usb device ?
Thanks in advance.
There is no simple procedure for figuring out what commands a USB device has. You need to use a combination of looking at the descriptors reported by the device, seeing if the device supports any particular USB device class, reading the USB specification, and maybe doing some reverse engineering using a protocol analyzer.
A good first step would be for you to use lsusb -v to print human-readable descriptions of the device's USB descriptors.
I have a embedded device that runs linux 2.6.37.
I want my application to know when the USB is connected.
Currently I can achieve this by pooling
/sys/devices/platform/musb/musb-hdrc.0/vbus.
However this approach does not distinguish between a USB charger or a USB host.
I found this udev approach but I don't think it's available in my version of the kernel. because I did not find any USB related nodes in my /dev. This discussing also shows that it might not be feasible, ether.
I also found linux hotplug and tried the netlink example, but I didn't see any output running the example when I connect/disconnect the USB cable.
What I want to do is to detect connection type on the device, when USB is connected, and prepare (unmount file system) and switch to g_file_storage if device is connected to a host, and do nothing if device is connect to a charger.
How shall I achieve this?
To achieve that, you can use the inotify(7) feature, available in all linux kernels to be awaken as soon as some device node gets created in /sys.
To know what type of device you have, you have to read the usb info from proper usb ioctl call (or if you are not a kernel interface expert, using the libusb interface) to get the device vendor, device id and device class fields coming from the device. Normally, the hotplug software gets informed on these clase of events (via a special socket). The most probably reason you don't get the device properly initialized is some misconfiguration in the config files for udev system, which normally has one entry for each possible device vendor/device id pair and allows it to load the appropiate device driver to control it. The process continues with the device driver module creating dynamically the actual devices, and they'll appear in the /dev/ filesystem as a consequence of some other kernel event to udevd.
Read apropiate documents in <linux_src>/Documentation (this directory directory belongs to the linux kernel source code, so you'll probably need to install it), and udevd(8) man pages to be able to add a new usb.
On 2.6.37 kernel, this could be done by polling
/sys/devices/platform/musb-omap2430.0/musb-hdrc.0/mode
If handshake with host is successful then it will read as "peripheral", if fail it'll be "idle".
I'm looking to attach some USB devices to my embedded Linux board.
It is an TI-ARM processor running embedded Linux, but I guess it could be any embedded Linux board.
If I purchase an USB device which has Linux support/driver, can this driver (generally) be re-compiled to work with the ARM architecture? (Instead of Windows ect.).
Yes, USB drivers can generally be expected to compile for other architectures other than x86. Of course this presumes that your board does have a host USB port. There are a few boards that have only USB device ports, and many SoCs have both USB host & device ports.
But successfully compiling the (USB) driver may only be part of the task.
Some (USB) devices may require additional packages of libraries and other drivers for interfacing to application programs. For instance a USB digital TV tuner requires numerous packages (V4L, ALSA, I2C driver, userland firmware loading) to actually work.
Clarification
These additional dependencies that you may have to build are not because of USB.
The dependencies are related to the type of device.
An Ethernet interface, whether integrated into the SoC or offboard using USB, would be easily configured for full support in the kernel (e.g. protocol stack) and userland (e.g. Busybox has ifconfig, ping and routing apps).
A PCI TV tuner would have the same dependencies as the USB tuner. But the embedded environment typically means that you don't have any/most of these multimedia dependencies already built/installed.
I'm researching ways to communicate with a USB device in Linux and would prefer to not write a Linux Kernel driver. I understand that libusb exists and is a user-land library that would work, but our embedded device doesn't support usbfs ( and would be really a pain to change kernels to add the support ).
So my question is basically this: Is it possible / advisable to communicate with a USB device by directly reading and writing to the /dev/USB or the udev file corresponding to the USB device thus bypassing the need for a custom Linux Driver and usbfs?
I'm hoping it's possible to communicate using the USB devices protocol just by reading / writing protocol packets directly through file-type read/write commands once the /dev/USB or udev device file is open.
Thoughts and suggestions please.
FOLLOW UP:
Since the USB device I needed to talk to is a USB HID class device, I was able to use libudev and the standard Linux USB HID RAW driver by reading / writing directly to /dev/hidraw0 ( or the appropriate /dev/hidraw device ). It wasn't necessary to write a custom driver for a simple USB HID device.
Jim, I don't think you can escape the need to write a driver and just manage to read the USB file in /dev. Because who defines as to what should happen when you do a read() on the USB device file? And who defines what action should be initiated when you invoke sysioctl()? Your driver! In other words, the device files are themselves incapable of anything until they are supported by the underlying drivers. In fact, you can treat the device files to be an abstraction of the underlying driver! So, no driver, no use of device file :(
I suggest you go through the following articles about how to write a driver and also understand the USB internals-
http://www.linux-usb.org/USB-guide/c15.html
http://www.linuxjournal.com/article/4786 ( Slightly outdated )
I am wondering, do you need a specific device driver to read a usb device in Linux, or should it just be able to be read. If I connect my cell phone or iPod touch to my linux box, it is not found is /proc/partitions and thus is not a mountable device by fdisks standards, though gnomes nautilus does in fact mount the iPod but not the windows mobile touch pro cell phone.
So I am interested, If I just wanted to read a device(iPod touch) in linux, how can I do so. How can I get a hold of a descriptor of a set usb device so I can read it.
Thanks all.
You can access raw USB endpoints under /dev/usbdev. There is user-space libusb that makes it easier.
Unfortunately there is no simple concept of "just read it" for USB devices (I am assuming that you are not referring to reading and writing the data on the USB bus that make up the USB protocol). In short, you always need a device driver for accessing a USB device and it is up to the driver to implement "the abstraction" of the device used by the system (disk, serial device, etc).