This maybe a linguistic question. I have checked the loop device on Wikipedia. It is just for mounting files as block device. But what does "loop" mean here? Its usage here is totally bizarre to me. I am not a native English speaker. So could someone explain this jargon to me in plain English? :)
Thanks.
It's short for "loopback".
The concept is also known as a disk image. I guess because driver calls to the image get passed along to the underlying driver of the physical disk. There is no actual loop involved; it is an additional level to a driver stack which is already several layers deep.
(I've written an encrypted disk image driver, and I find the "loopback" terminology incorrect and confusing.)
I guess this term comes from the communication realm when sometimes it is needed to test the communication system by simulating a peer using a proxy circuit loop.
The concept came also to UNIX networking where loopback network interfaces do not send network traffic to the medium.
The same concept in file systems loop means that the file system driver does not really goes through the hard disk IO stack and, instead, ends using a plain disk image file for IO.
Related
I am posting here concerning the emulation of computers on the local network, without destroying the local network.
When a computer connects to wifi on your local network, the computer can be seen in the "Network" section of Explorer(on Windows) and can be addressed via internet protocol.
My Goal: I would like to create a program such that I could receive streams of data from a remote computer via radio waves. The communication would be full duplex, there would be a transmitter and a receiver on both ends.
My Idea: I would like to utilize Qt to create an application which would receive and demodulate the radio waves like sound (through OpenAL buffers) which would act similarly to a driver program for the emulated computer connection, without destroying my connection to the local network. In this way, I believe that some truly novel things could be done, as I could for instance, use PuTTY one the emulated connected computer remotely while browsing my local network and the internet from my "base" computer.
Extended explanation: I want to perform a weather balloon project, sending a small computer (likely Raspberry Pi3) via a weather balloon to the far reaches of our atmosphere. One of my worries is being able to communicate with the device, such as receiving locational (telemetry) data in real time and being able to (potentially) retrieve arbitrary data in real time.
I understand that I may very well be approaching this question in the wrong way. There are probably existing systems out there that grant telemetry data and some arbitrary means to transfer file data, of which I am unaware. But from what I have seen, I also cannot find a device that utilizes this approach (packet radio emulation of a computer on the network). I have a personal curiosity towards this approach, and thusly will accept the answer which follows most in line with this approach.
P.S: Video which inspired this idea:
https://www.youtube.com/watch?v=Ueb5JG0dCL8
What you're trying to do is called software-defined radio, and is rather popular. Modern computers, even little ones, are more than powerful enough to do the modulation/demodulation entirely in software.
There's very little left for you to do other than designing the RF channel, purchasing often open-source hardware, and using existing open-source SDR implementations out there. The input/output to your Qt program would be either a QIODevice-like data stream that you'd couple to the SDR library's data scrambler/descrambler, or a packetized data stream that you could run some higher-level protocol on.
Do note that unless you limit yourself to an industrial license-free band, you are likely to need an FCC license to operate the transmitter, and an FAA license to launch the balloon.
Your question is essentially off-topic here. It probably belongs on amateur radio stack exchange under the [sdr] tag.
If you're thinking of implementing a complete WiFi stack using SDR, I'd like to discourage you: it's patent-encumbered up the wazoo, so no open-source implementations exist, and the sheer amount of standardese you'd have to wade through to do a compliant implementation is staggering. We're talking on the order of 5,000 pages of standardese, where almost every other sentence is important so if you ignore it, you're not compliant.
I'm currently building a c++ program (with Qt) to take picture from a camera device. This part is actualy done, now I need to control 8 flashs divided in two groups in an automatic way.
The flash I already use are from ELINCHROM http://www.elinchrom.com/ and this device seems to be perfect for what I need but I could not find anywhere a way to control it from a different application than the one elinchrom propose.
Do you know if what I intend to do is even possible? If a solution exist with another brand I will also take it.
Thank you in advance for any replies, and please excuse my english.
Should be possible; the driver guide states that the driver is really a USB serial port driver. That means you can probably reverse-engineer the protocol.
My main goal is to create an advanced program for manipulating the packets that route within my network via the router. Let my program have total control over the router. Set the download/upload speeds to my inputs, apply the effect to certain devices within in my network. Block upload or download traffic. Set second delay for either the upload or download speed. Specify % of loss packets, and the list goes on.
The problem is that I don't know where to start. I know most languages at the very most basic level. I'd like to create this program in either C, C++ or C# but I don't know yet. What else do I need to know before creating this program? Winsock or something? Winpcap APIs?
This goal is my motivation to learn programming to the extreme, and I'm really looking forward to it.
Thanks in advance!
Hmmm I guess you would want to look at pcap(?):
pcap
Check out:
http://beej.us/guide/bgnet/html/multi/index.html
'Beej's Guide to Network Programming
Using Internet Sockets'
All you could possibly need to know about programming sockets for capture and manipulation.
If I were you I'd write it in C, I'm writing a similar project at the moment in C++ and it's hell but too late to stop and start again.
Hope that helps.
Bear in mind that you either need a router that you can re-program or you need to use your PC as a router to do this.
Either way you want to look into how IPTABLES are implemented.
I've never seen Desktop Windows used as a router only Windows Server, though it may still be possible. libpcap is for packet capture, but not interception as I understand it. Programs like Wireshark use it to monitor copies of packets, but not to modify them. If you want to attempt this, my impression has been that there is a lot more documentation and tools for doing something like this with NetFilter/IPTables on Linux. You can even install something like OpenWRT on a compatible router and get a small, cheap Linux router, though having Desktop Linux will probably help for development. The NetFilter QUEUE library can be used with some IPTables firewall rules to redirects specific (or all) packets to a regular user program. That program can then read the packet and modify it or even request it to be dropped.
http://www.netfilter.org/projects/libnetfilter_queue/
If you want to manipulate network traffic on a Windows machine (as you mentioned), you will need some extra software. This operating system wont give you the full control over itself, which is fine for some reasons.
I think what you want to do, should be done with either winpcap or win10pcap if you are using Win10. These packages contains a windows driver and the libpcap user space library.
has anyone some kind of documentation how to implement an own flashing-procedure for an atmega8-microcontroller ?
when searching, i have only found tutorials, on how to flash custom software with the normal flashing-software (in most cases atmels flip), but i haven´t found any documentation, how you would implement it in your own software. eg. what are the commands in which timings and with which responses from the microcontroller.
so, thank you in advance
You program the chip by communicating with it through SPI lines while it is in reset. You can find details in the chip's datasheet.
You can't do that directly from your PC, you need to have an external hardware device (even if it is a mere level converter connected to your serial/parallel port). How you communicate with that device depends on the device.
If you want to implement bootloader functionality, you should take a look at boot_page_write() function in avr-gcc help. Basically what you need is the data stream from PC/other uC which will accumulate in RAM until you have enough to write one page.
You can search for AVR Universal Boot loader for example how it can be implemented.
I am trying to connect to a single USB device using the USB host port on an Atmel processor. I have an embedded system with limited memory and no OS. I want to implement a simple dedicated host to interface to a single USB slave device.
Can anyone guide me to a simple USB host implementation?
The processor is the Atmel AT91SAM9261S.
First of all if i remember correctly AT91SAM9261S have OHCI usb controller on board and you need to implement at least simple host controller driver (you can take a look on Linux implementation) . Depending on the transfer types your device will be using it might be not very hard - to very hard :) There is no trivial way to implement usb stack.
After implementing a controller driver you will need to take care usb device enumeration part take a look at Chapter 9 of USB spec. And only after this you can start implementing your device logic.
For simplified use case there is a lot of code that could be omitted, but without good usb background is hard to decide what is relevant and what is not.
Any way if you are looking for commercial solution my company can provide one.
I've used the RTUSB-32 stack from On-Time. It is a small foot print stack and was easy to integrate into our environment and the documentation is good. They abstract out nicely the needed support so that it is completely platform and OS neutral and has a relatively small number of hooks you need to provide to it - ie: It is well encapsulated.
Since you get all the source, you'll see that the code is not the most well constructed code in the world, certainly, but it can be deciphered without a whole lot of work if needed. In any case, it basically "just works" without issue. We have had it running in some products for a few years now and have only run into one compatibility problem with the stack where it wasn't quite doing auto-discovery quite right with a certain type of USB 2.0 hub. We sent them a sample of the hub and they had a patch for it within a few days. Hard to beat that. Overall, I consider it a good value and certainly beats sitting down to write the thing from scratch.
This would be so much easier if your device didn't have to be a host :-P, because Atmel provides example source code for USB devices. If I were you, I'd look into using one of the USB-loving RTOSs on Atmel's AT91SAM third party page which might entail the USB stack from jungo as suggested by Ilya.
If you do write your own OHCI driver, libusb could be helpful as an implementation of the upper layers of the USB stack.