I have to discuss the codeflow of the USB host controller. This USB host controller is the interface between the device and the OS. There are numerous USB devices (eg.keyboard,camera,mouse,etc).
Where will I find the code to see how the communication between the USB device and OS happens through the USB host-controller ?
Download the Linux kernel source code, and start reading the code in drivers/usb. Here an online reference, and the README about the USB-tree
I suggest you to take a look at USB host controller specifications - UHCI/OHCI/EHCI/XHCI because this knowledge will be necessary to understand whole USB stack in linux kernel.
You may also download some example sources provided by several embedded microcontroller producers (i.e. Atmel). Probably those drivers will be easier to analyse than linux sources.
Related
I am trying to understand how can I write tasks for VxWorks. I have VxWorks on a board that is mounted on a development board.
I can access the board through Putty and a serial terminal connected to the UART of the system. How can I write other tasks (maybe to communicate with other UARTs or other Serial Interfaces) ?
And how do I know where to find the documentation describing how I can access those serial interfaces? (for example write/read methods, which file to include etc)*
Thank you
VxWorks is cross development environment, so you need a licensed development system on Windows or Linux desktop to create applications.
Then you load the compiled code on the target reference board as process/RTP or LKM/DKM. How you get it there varies by board: FTP, TFTP, removable USB or SD card....
At the C shell on booted system you can start a task in the kernel context with any public symbol. But if your working with deployed system, it shouldn't have the C shell, that's a serious security risk :)
Try..
-> sp printf, "\nHello VxWorks World!\n"
I am currently developing a driver for an HID device on a FreeBSD system. The idea is that the driver writes to the device's registers through the Control Endpoint. From then on the device acts according to the data fed.
Since I have just started out on drivers, I am following a guide book (I would name it here but I don't know if I can? ). This book tackles a USB ULPT (Printer) driver, explaining the basic driver for a USB device. However when I am trying to implement these concepts to the HID device, I am having trouble, more specifically when it comes to identifying and probing the device.
Since I haven't found much material online, I was wondering are there any guides/books or tutorials I can follow which tackle the development of an HID device driver on FreeBSD or at least Linux systems. A pointer (pun intended) to the right direction would be enough to get me going again.
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.)
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.
I am currently practising with USB programming on an AT91SAM9G20-Evaluation Kit. I learned much about USB devices and USB device port drivers while "playing" with the ATMEL provided USB device port projects (CDC-driver, ..).
But now I'd like to write a small driver to controll a wireless stick
which I plugged into one of the boards USB-A Host Ports.
I read a lot on Stack Overflow, the OpenHCI specification and even found some libraries on the net, but I am not sure if it's a good way to implement my own stack without any "good" knowledge in USB Host Port programming.
Is there a small and easy way to control the wireless-stick at the boards USB Host port? (like using the USART-Interfaces?).
I am also keen to hear hints on how to implement RTUSB or libUSB in to the AT91.
You can download AT91LIB version 1.9 from atmel from this page
The usb host libraries are under at91lib/usb/host. They're not the complete package you need though since they're just the OHCI driver -- you still need a USB driver and class drivers to implement what you want.
You could try an RTOS with USB Host support like rt-usb32