I’m on process of developing my own Operating System based in Linux.
This week we’re aiming to implement very simple USB device driver , which is quite hard to get basic algorithm .
However commonly it’s hard to find out some sources aside from commercial linux system.
And I want to get some advice about this .
Plus, I do all these stuffs on Ubuntu , using QEMU emulator.
I’ve done simple file system and hard disk device driver so far.
Help me out how to implement USB device driver with very sime ideas.
Thank you !! :)
Implementing USB is quite the task. First you must have a working PCI(e) enumerator or other form of finding the USB controller. You then must find out which of the four most common controller types it happens to be. Each controller type is completely different from the previous and must contain its own driver. You also need a standard USB interface that is independent of the controller type.
Taking on the USB is quite the task, but in my opinion a very interesting and enjoyable task. Enjoyable enough, that I even wrote a book about how to do it. It explains how to find the controller(s) via the PCI(e) bus, how to setup this bus, how to detect the type of USB controller--UHCI, OHCI, EHCI, or xHCI--and how to send and receive data packets to/from attached devices. This book was written exactly for the purpose of those of us creating our own operating systems and adding USB support to them. The fact that you are basing your OS on Linux should not matter since the book does not rely upon any existing OS to accomplish this task, other than the example programs relying on memory allocation, which is easily modified for your developing platform.
Might I say that if you do take on this task, it will be a difficult task, but it will be an enjoyable task. In my opinion, the USB is the most enjoyable part of this hobby of ours.
Related
I want to make a network camera, stm32 through the camera to collect images, and then sent to the server through the WIFI module. As 1 second need to transfer a lot of data, so I would like to use the USB interface wifi module program to achieve. Or what better solution to achieve.
Thank you!
I think that you have no idea how the USB works.
You have a couple solutions.
Use a wifi module with SPI interface.
Use a SOC like CC3200.L
Use ESPxxxx module or similar (RTL8710)
You can of course try to use STM with host usb interface, but you will have to implement the USB host stack + driver for USB wifi module + network stack (eg TCP/IP stack). But it is quite complicated as the STM ones are not very good, there are some better paid ones - but expensive. USB host is not easy to implement.
If you want to go along the "networking over USB" path on STM32 (and I'm assuming you're not planning to buy any commercial drivers) it's going to be rough for you.
When it comes to USB, vast majority of the WiFi dongle drivers are proprietary and unless you're on an operating system such as Windows or Linux you're out of luck, unless you want to for the reverse engineering or porting at least parts of the drivers from Linux. With the USB you can think of using the USB-ECM (ethernet over USB) class, but two things here. One - ST doesn't provide any free implementations of this class so you're down do searching for it or implementing it yourself. After a bit of googling I've found one instance of this on githbu, although I havent tested it myself. Second thing - this is no longer wireless as you'll need to be connected to some kind of host providing internet connection, at which point it's probably better to not use USB-ECM and networking at all and just send data using a class that can be implemented easily (USB-CDC or USB-HID). I'm a bit worried about the throughput here.
You can also try to find WiFi modules that are connected over other interface. Generally those modules are connected over UART, some over SPI. This way, integrating it with the TCP/IP stack will also be up to you, at least when it comes to implementing the WiFi module protocol (most likely AT-commands) and implementing network interface so that the stack can "talk" to it. In this approach, I'm almost sure that you'll lack the throughput required for your application.
Personally I'd strongly suggest trying Ethernet if that's an option for you. It's going to be highest bandwidth (which you're going to need), plus it's most "out of the box". There's multiple projects implementing various applications using a free LWIP stack over this interface, including examples generated by ST's CubeMX.
I have these related questions:
Does anybody know how an OS gets to know all hardware connected on the motherboard? (I guess this is called "Hardware Enumeration").
How does it determine what kind of hardware is residing at an specific IO address (i.e.: serial or parallel or whatever controller)?
How to code a system module which will do this job? (Assuming no OS loaded yet, just BIOS).
I know BIOS is just a validation and an user friendly interface to configure hardware at boot time with no real use after that for most modern OS's (win, Linux, etc). Besides I know that for the BIOS it should not be difficult to find all hardware because it is specifically tuned by the board manufacturer (who knows everything about it!). But for an OS or an application above BIOS that is a complete different story. Right?
Pre-PCI this was much more difficult, you needed a trick for each product, and even with that it was difficult to figure everything out. With usb and pci you can scan the busses to find a vendor and product id, from that you go into a product specific discovery (like the old days this can be difficult). Sometimes the details for that board are protected by NDA or worse you just dont get to know unless you work there on the right team.
The general approach is either based on detection (usb, pcie, etc vendor/product ids) you load a driver or write a driver for that family of product based on the documentation for that family of product. Since you mentioned BIOS, win, linux that implies X86 or a PC, and that pretty much covers the autodetectable. Beyond that you rely on the user who knows what hardware was installed in the system and a driver that came with it. or in some way you ask them what is installed (the specific printer at the end of a cable or out on the network if not auto detectable is an easy to understand example).
In short you take decades of experience in trying to succeed at this and apply it, and still fail from time to time since you are not in 100% control of all the hardware in the system, there are hundreds of vendors out there each doing their own thing.
BIOS enumerates the pci(e) for an x86 pc, for other platforms the OS might do it. The enumeration includes allocating address space for the device based on pci compliant rules. but within that address space you have to know how to program that specific board from vendor documentation if available.
Sorry my English is not very good.
Responding questions 1 and 2:
During the boot process, only the hardware modules strictly necessary to find and start the OS are loaded.
These hardware modules are: motherboard, hard drive, RAM, graphics card, keyboard, mouse, screen (that is detected by the graphics card), network card, CD / DVD, and a few extra peripherals such as USB units.
Each hardware module you connect to a computer has a controller that is like a small BIOS with all the information of the stored device: manufacturer, device type, protocols, etc
The detection process is very simple: the BIOS has hardcoded all the information about the motherboard, with all communication ports. At startup, the BIOS sends a signal to all system ports asking the questions "Who are you? What are you? How do you function?" and all attached devices answers by sending their information. In this way the computer knows how much RAM you have, if there is present a keyboard or a mouse, which storage devices are available, screen resolution, etc ...
Obviously, this process only works with the basic modules needed to boot the system, and does not work with complex peripherals that require specific drivers: printers, scanners, webcams ... all these complex peripherals are loaded by software once the OS has been charged.
Responding question 3:
If you wants to load a specific module during the boot, you must:
- Create a controller for this module.
- If the peripheral is too complex to load everything from the controller, you must to write all the proccess to control that module directly in the BIOS module, or reprogram the IPL to manage that specific module.
I hope I've helped
Actually, when you turn on your system, the BIOS starts the IPL (Initial program load) from ROM. For check the all connected devices are working good and also check the mandatory devices such as keyboard, CMOS, Hard disk and so on. If it is not success, it gives an error flag to the BIOS. The BIOS shows us the error through video devices.
If it is success, the control of boot is transferred to BIOS for further process.
The above all process are called POST (Power On Self Test).
Now the BIOS have the control. It checks all secondary memory devices for boot loader of the OS. If it hit, the bootloader's memory address is transferred to RAM.
The Ram started to execute the bootloader. Here only the os starts to run.
If the bootloader not hit, the bios shows us the boot failure error.
I hope your doubt clarified...
As far as I understand it, any program gets compiled to a series of assembly instructions for the architecture it is running on. What I fail to understand is how the operating system interacts with peripherals such as a video card. Isn't the driver itself a series of assembly instructions for the CPU?
The only thing I can think think of is that it uses regions of memory that is then monitored by the peripheral or it uses the BUS to communicate operations and receive results. Is there a simple explanation to this process.
Sorry if this question is too general, it's something that's been bothering me.
You're basically right in your guess. Depending on the CPU architecture, peripherals might respond to "memory-mapped I/O" (where they watch for reads and writes to specific memory addresses), or to other specific I/O instructions (such as the x86 IN and OUT instructions).
Device drivers are OS-specific software, and provide an interface between the OS and the hardware.
A specific physical device either has hardware that knows how to respond to whatever signals from the CPU it monitors, or it has its own CPU and software that is often called firmware. The firmware of a device is not specific to any operating system and is usually stored in persistent memory on the device even after it is powered off. However, some peripherals might have firmware that is loaded by the device driver when the OS boots.
There are simple explanations and there are truthfull explanations - choose one!
I'll try a simple one: Along the assembly instructions, there are some, that are specialized to talk to peripherials. The hardware interprets them not by e.g. adding values in registers oder writing something to RAM, but by moving some data from a register or a region in RAM to a peripherial (or the other way round).
Inside the OS, the e.g. the sound driver is responsible for assembling some sound data along with some command data in RAM, and the OS then invokes the bus driver to issue these special instructions to move the command and data to the soundcard. The soundcard hardware will (hopefully) understand the command and interpret the data as sound it should play.
I have been reading on linux kernel development and device drivers for a while. I feel ready to give it a go on a real piece of hardware. I would like to write a driver for a, preferably usb (otherwise pci), device for a desktop computer. But every device I seem to think of is already supported (including everything I own atm). So, would welcome any suggestions.
P.S. Willing to buy it, provided it's under £100 (150$).
Anything really practical has already been done out of necessity. My vote would be for something like http://www.amazon.com/Cheeky-Computer-Controlled-Missile-Launcher/dp/B004AIZV48/ref=pd_sim_t_1. It's fun, inexpensive, and currently Windows only.
The protocol should be pretty simple, but will give you good experience on debugging the USB channel in order to figure it out. And when you are done, you'll have a cool toy :)
USB-based devices are generally well supported at the kernel level. What this means is that u rarely have to write a device driver for each and every USB devices at the kernel. THis is because applications can easily use libusb (and several other userspace USB libraries) to talk to the device.
If you look into the USB code in the kernel, you can see that it is among the most complex implementation of all the hardware protocol, but it is also generic across different USB devices. I have done porting work for USB devices before, and trust me, libusb is good enough.
Check it out (for example):
http://libusb.sourceforge.net/doc/examples.html
You could port the Enttec Open DMX USB Interface driver to latest 3.x kernels.
git clone http://git.hbels.com/public/dmx_usb_module
libusb way sounds more appropriate to me too though.
What is the best way to realize wireless communication between an embedded system (based on an AVR controller) and the iPhone? I think there are only two options: either WiFi or BlueTooth. The range is not really a problem, since both devices should stay in the same room.
I have no idea, if there are any useful WiFi boards that can be connected to an AVR based microcontroller system (or any small microcontroller), any hints would be highly welcome.
I guess the better solution would be BlueTooth, but there is also the problem: which BlueTooth board is best suited for attachment to an AVR system, and is it possible to use the iPhone BlueTooth stack for (serial) communication over BlueTooth with the AVR device.
I hope that somebody already realized such a system and can give some helpful tips...
You can get modules for both WiFi and Bluetooth that will connect to an embedded system through a UART interface, however a WiFi module will have far more processing power than your AVR microcontroller, often with spare capacity and I/O to execute additional user code, so connecting one to an AVR maybe somewhat redundant in many cases.
Bluetooth modules are simpler, less expensive, and the data-rate is better matched to the AVR's capabilities. For example these Parani modules. I have used them between an embedded system and a Laptop PC's Bluetooth, so given appropriate communications software, there is no technical reason why it could not be used with an iPhone I think. However this may be the flaw, on the PC the device was recognised as a virtual serial port, I don't know whether iPhone supports 'legacy' communications in quite the same way.
For comparison, a WiFi solution
From what I know, BlueTooth is very limited on the iPhone: There is only very few BlueTooth-Profiles implemented, and - even if they can be extended with a jailbroken iPhone - I doubt this is easy to use from the application layer.
On the other side, transferring via WiFi requires a lot of processing power and memory since much more things have to be implemented before you can even start transferring data: 802.11, cdma/ca, arp, tcp. That's a big task.
Is it an option to build a hardware extension to the iPhone ? You might be able to get the serial connection and power out of the dock connector. Then even ZigBee could be very helpful.
Here's an article you might find helpful. I would lean toward a WiFi solution just because of the added flexibility available.
http://www.embedded.com/design/networking/215801088
-t
Some of the other people at the office have done AVR <- Bluetooth -> Symbian and AVR <- Bluetooth -> PC solutions without trouble. There is lots of info, reference designs and source available. I have no idea of how hard it would be to use Bluetooth on Iphone.
The exact module is probability also not important as long as it got some type of serial interface (I2C,SPI) to interface to the AVR and some source code show how to use the module.
Is it an 8-bit or 32-bit AVR? For the AVR32 processors there's support
for WiFi in the Atmel 1.5.0 Software Framework using SD-card-mounted
WiFi modules from HD Wireless (http://www.hd-wireless.se), including
an IP stack (lwIP). Be aware that you need Ad-Hoc (IBSS) support to
connect directly to the iPhone.
There is WiSnap kit. It can connect directly to a standard RS232 interface or through the TTL UART interface to embedded processors. We are planning to use it in our project. It also has Ad-Hoc support.
There are some usage examples and an iPhone application for connection setup.
http://serialio.com/products/mobile/wifi/WiSnapKit1.php
What are you trying to communicate between your AVR and the Iphone? The Iphone is made for the web along with everything apple (which AVR's are decidedly not). So what works well is an embedded device that exposes a web-interface. Like the Transmission bittorrent client on Linux. Also nowadays many low-power small form-factor linux platforms exist that will allow you to do this.
For instance Gumstix has an ARM based platform that runs linux and includes WiFi (Overo Fire).