I'm commissioning an embedded system (AM335x, Yocto with kernel 3.19). When I plug in a USB VCOM adapter, I get the encouraging message:
usb 2-1: new high-speed USB device number 3 using musb-hdrc
but I never receive the longed-for follow-up which should look something like:
usb 2-1: New USB device found, idVendor=????, idProduct=????
So, the question is, what system component is generating the first message, and failing to generate the second?
The obvious answer seems to be musb_hdrc, which I believe is a kernel module. I do not know through what mechanism a kernel module is configured - is that through the .config file, as for the kernel? And I have no idea what setting this module might have (if it is involved at all) that would cause it do nothing upon noticing my USB device.
Can anyone shed any light on what might be going on, here? It's, in most respects, an off-the-shelf Yocto build.
Thanks
Here is a very good kernel documentation on musb. May be you can go through the source files.
Related
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".
My goal is to create a virtual USB char device (not block device) for Linux 2.6.32 and above (I use debian squeeze) that would be recognize by the system.
I would like that this device be listed with lsusb as a normal USB device, and that every application could use libusb in order to open the device, and send control message, and make bulk write/read. But behind this virtual device, it's behavior would be set by my application. I want to set it's product ID, it's vendor ID, answer to USB status, and bulk read.
I've read some posts about how to use USB/IP in order to create a virtual USB device, and that's exactly what I want to do
Installation and emulation of virtual USB Device
http://breaking-the-system.blogspot.fr/2014/08/emulating-usb-devices-in-python-with-no.html
But unfortunately, when I tried with 2.6.32 kernel and above, I didn't succeed making it work. So I looked at how to create a kernel module that would create the virtual device :
http://pete.akeo.ie/2011/08/writing-linux-device-driver-for-kernels.html
This one looks great also, but the sample provided doest not indicate how to make it an USB device.
I've seen some post talking about it with windows but none that could help me with Linux.
I would like to avoid buying some USB programmable cards when it can be done with software.
Have anyone any leads on how to make the first methods works under newer kernel, or convert the sample code of the second method for making an USB device ?
I have fixed the code of http://breaking-the-system.blogspot.fr/2014/08/emulating-usb-devices-in-python-with-no.html (first method using USB/IP) to work with linux 4.3.
In the original code are missing USB requests like set configuration and get status. Without the implementation of all USB requests used for the OS driver the code will not work.
The fixed code can be downloaded in https://github.com/lcgamboa/USB-Emulation .
I guess raw-gadget kernel module is the thing that you want?
you can check the dummy_hcd and tests directory inside the repo, it will guide you how to create a virtual USB device
My question is simple, is there a way to see in a terminal what usb devices do I have connected to my computer in real time?
I already know lsusb, but it just show me the devices on the moment I ask it, I would like to be able to see if one connects and disconects at some point.
Edit: Thought the answer marked underneath gives a good alternative, in order to debug the program I was working on I found usefull useing the C++ function
std::system("lsusb");
This way I could check if I had lost or not the USB device.
Sure there is, you can use the udev device manager for kernel.
Moreover you can define rules to detect plugged/unplugged devices you are interested e.g. in your case usb devices.
Here is a tutorial on how to write a udev rule
I am trying to find out a high-level overview of how the USB storage driver works in Linux. I'm looking for a simple article or even a picture/flowchart describing how it works.
Basically, I'm looking to get these questions answered:
When you plug the device into your computer, what happens? Is there a daemon that picks up on it, or does the event trigger an interrupt somewhere? Does the core USB driver read information about the device before passing control over to the USB storage driver? How does it decide what type of device it is? How does the device get mounted, and what allows it to communicate with the computer's filesystem? When I copy a file, what does the data flow look like in the kernel?
I hope the question isn't too vague - I tried Google to no avail, so I'm wondering if anyone knows any articles or diagrams that can explain this, or perhaps if they can explain it themselves without too much effort. Thanks.
No, it is a very good question.
The block writing is going in linux with the block device layer. The filesystems are working with this block dev layer.
If this layer wants to write something out, says it to the driver of the usb master device. This driver is talking with the usb controller chip of the motherboard.
This chip is very simple: the usb is practically a serial port, with a lot of extensions, mainly targeting the autoconfiguration and the power management. But basically, you can write out bytes, and read in bytes.
Your questions:
When you plug the device into your computer, what happens? Is there a daemon that picks up on it, or does the event trigger an interrupt somewhere?
The device (usb slave) says the master (in the motherboard): "I am here". The usb controller chip gets the message and says it to the kernel (normally) with an interrupt. The kernel reinitializes and rescans the usb bus, and says the udev: "here is a new 1234:5678 usb device on the usb tree 1.3.5"
"How does it decide what type of device it is?"
Usb devices have a vendor and model id, and they can say this on ask. Google for "usb ids".
"How does the device get mounted, and what allows it to communicate with the computer's filesystem?"
The kernel only loads the driver and says the udev (which is in userspace): "Here is a new block device on device number 22:16". From this, udev tries to mount this with some userspace daemon, it is already distribution-dependant.
I am using i.mx 287 EVK from freescale for my application development.
I am ported linux kernel and rootfs successfully.
But the problem is my hardware does't detect the USB stick if connected.
Nothing changes in /dev directory nor anything appears in log (dmesg).
Kindly help me resolve it.
Hardware has both usb host and device ports.
Basic things i would check :
Check with other USB.
Connect a USB Mouse or USB keyboard. Check if they are working. Check if the devices are getting power or not.
If you are not getting the power, definitely there is a problem with the kernel configuration.
Do make menuconfig from the linux folder, go to USB drivers section and enable all the flags that are needed for a USB pendrive to work.
Easy method would be to take the configuration file(kconfig) of a working linux kernel, copy it inside your kernel, compile it and run it. It should work
ITs been a while that i did the above things. But this should help you out of your current problem.