We are developing an embedded device running Linux, which needs to act as a usb serial gadget and connect to android phones for different types of data transfer. In order to initiate the communication with the host usb (android phone), I need to detect whenever the USB host is connected to the device. I came to know about writing udev rules in order to run an executable on usb host insertion/removal, but We already have a main C program that manages all of the device's main functionality. I would be running a thread in this program which would be responsible for this communication. Is there any way by which I can receive the USB hotplug event in this thread. I am really trying to avoid using loops in this thread so that it doesn't get CPU intensive. So is there any way by which I can receive the USB hotplug event?
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Development platform: TI davinci processor with Linux OS
I am developing C program which receives user command over serial port and does the corresponding task. Basic task is to start and stop the video recording. And for retrieving the video to host pc from the embedded device, usb interface is used.
The partition used for storing the video file is loaded as USB gadget mass storage device using following kernel module for the user to save the video on host pc.
modprobe g_file_storage file=/root/usbstorage
But i want to load(or some otherway) this kernel module from the c function whenever user send a command to connect the embedded device to host. And disconnect whenever disconnect command is received.
As of now I'm able to load this module only from the shell.
Could any suggest any possible way of doing this from within the c-program.
The embedded system that I'm working with runs the 3.18 Linux kernel and when connected to a PC acts as a composite USB device with HIDBP functionality (allows you to connect a keyboard and mouse to it). However, the problem I'm having is that a keyboard or mouse connected to it doesn't seem to wake up the host PC when it goes into full system suspend (a mouse connected directly to a PC can wake it up though). I'm just wondering, is this a linux kernel bug and if so how would one go about fixing it?
For reference, this feature has not been implemented for USB HID composite devices in the mainline kernel as of version 4.10.17
I have an embedded Linux solution and want to create a command service over serial USB. The idea being that when a computer connects to my embedded via USB, they see a serial device and send serial commands to me through that port and I send responses back.
I need some help in the direction to proceed. Do I need to emulate a serial device so they see me as a COM port? Is there build in Linux solutions to broadcast my details as a serial device? Are there code examples? I can see block devices connect with my embedded solution like a USB storage device. When I plug into another computer, I would like it to see me as a serial COM port.
I just need help in the direction of which path I should go down to solve this.
Thanks in advance.
What you are looking for is the Linux USB serial gadget. The Linux USB gadgets framework allows devices to behave as a variety of standard USB devices, including serial devices, Ethernet adapters, and mass storage devices.
Note that USB gadgets will only work on targets with a USB controller that can be set to operate as a USB device. Not all USB controllers and target devices are compatible with this configuration. For instance, most PCs have a host-only USB controller, and the Raspberry Pi Model B is not compatible with gadgets because it contains an embedded USB hub upstream of the USB ports. (However, the Pi Zero is fully compatible with gadgets.)
Non-programmable Xbee modules should be configured through a PC (with XCTU) or other devices like Arduino... but can the programmable xbee modules (like xbee-pro zb s2b) autoconfigure themselves, without being connected to another device like a PC or Arduino, by running code stored in their memory?
I mean, can they run orders like the ones you run through XCTU but programming them in the internal memory code? Like scan energy of every channel, select a channel, set a PAN ID, configure the different parameters of the device...
Thank you
Yes, the development kit includes an API for sending AT commands from the co-processor to the radio on those boards.
There's also a passthrough mode that relays the host computer serial port through to the radio processor, which can help with initial setup/configuration of the modules like you might do during manufacturing.
To answer your question:
I mean, can they run orders like the ones you run through XCTU but programming them in the internal memory code?
No. You can not program a sequence of orders/commands into the internal memory of the device. To do anything meaningful the device needs to be "driven" from a host PC or MCU that can send the AT Commands.
If you want 1 device solution that does not require a Host MCU then you will need to use a ZigBee SoC (System on Chip), such as the CC2538 - http://www.ti.com/product/cc2538 running a ZgBee SDK (Software Development Kit) - http://www.ti.com/tool/z-stack (ZStack-Home). However this will require you to develop the ZigBee application SW.
Regards,
TC.
My question is going to be rather vague but I will try to explain as detailed as I can what I am trying to resolve.
Trying to learn Linux kernel USB stack I have started to think of making a simple USB driver for my Atmel evaluation board based on ARM M0+ MCU to run away from Windows tools (Visual Studio plugin).
I have spent few days learning kernel's USB API and come to conclusion of how to make this. My driver aims to make my board connected to PC through USB cable act like a simple USB flash drive. Making that I then can easily program it with a new version of firmware written by me.
I have found that I need to find out specific interface (I am talking about interface in terms of USB specification, not interface we used to use as a code abstraction) that holds an endpoint (pipe) responsible for interaction with flash memory. And then I can map it to character device and interact with it using standard I/O operations that are described in struct file_operations structure.
Simply using cat on /proc/* file descriptor that was created by USB Core subsystem I have investigated that interface responsible for interaction with flash memory holds bulk endpoint (likewise, this terms come from USB specification, CMIIAW) that act as a "descriptor". Linux kernel USB Core subsystem gives neat interfaces to talk to different kind of endpoints whether it control, interrupt, bulk or asynchronous endpoint.
Now I have come closer to my very question.
Also the main transfer unit in communication between two USB devices is abstraction called urb - you allocate it, you fill it, you send it to USB Core subsystem, you read it if it was IN type of urb and, finally, you free it. What is confusing for me and tightly related to my question is the next API include/linux/usb.h:
static inline void usb_fill_bulk_urb(struct urb *urb,
struct usb_device *dev,
unsigned int pipe,
void *transfer_buffer,
int buffer_length,
usb_complete_t complete_fn,
void *context)
Assume I have obtained an information from board's datasheet about where to write a program code. Let's say, we have 0x00100 - 0x10000 memory region. I will compile my code, obtain a binary and then using standard Linux tools or writing a simple user-space wrapper application I will use lseek to set file's offset to 0x00100 and write system call provided with a buffer (binary compiled previously) and it's length.
In kernel space, I will have to allocate urb in write system call handler, fill it with a buffer sent from user space and submit this urb to USB Core.
BUT I can not find a way how to specify an OFFSET set earlier by lseek. Do I miss something? Maybe I missed some concepts or, perhaps, I am watching in a wrong way?
When your embedded Linux device acts as a USB mass storage device, the flash as a peripheral on Linux device is unmounted, and the gadget driver is loaded. Linux then loses control to the flash, and now the PC connected to your Linux device fully controls the flash. This is because a flash as a USB device can only has one USb host.
The gadget driver works purely in kernel space. It does not receive or transmit data from/to user space. It calls vfs_read() and vfs_write() to access the files on the flash, with an field offset. The offset is got from the USB commands sent from your host - Windows PC.
There is no way to specify offset using USB subsystem's API. I misunderstood whole conception of USB as communication protocol, unwise me. You must first learn underlying protocol your device uses to communicate with others.
If your device acts as a USB HID device then learning specification of how to exchange data with USB HID device is the way to go. If there is something proprietary then you can do nothing but reverse engineer it (listening USB packets with a sniffer on system where a driver for your device exists).
As for my board it has embedded debugger that serves as a communication module besides being debugger itself. Specifically, my device is equipped with EDBG and here is a link on description of protocol it uses for communication.