UNIX for Advanced & Expert Users

Hi,

I have posted several times regarding my application.

In a nutshell, I have a server application that logs attached instrument data over USB and Ethernet. My restriction here is having two wires or more to plug all instrumentation in - at least one for USB and at least one for ethernet.

The solution for the USB instrumentation is to route them through a hub into one wire to plug into the computer.

I have seen several low-cost Ethernet->USB as well as USB->Ethernet adapters. I understand that they both get data to your computer but thinking from a lower-level point of view, how does the computer see the data?

For the Ethernet->USB adapter does this mean that data that was initially sent from an instrument in TCP protocol arrives at a /dev/ttyUSB* port in USB fashion? Would I connect to it in my program via accessing the USB port?

I am sure the answer is quite simple but i'd like to know before I order anything up.

An example of one of the units I am looking at is:

http://www.thesource.ca/estore/produ...2b1IULx3PD_BwE

Thanks in advance for your help.

Think of it this way -- a serial cable is like a composite television cable. You plug it in and it shows up on the TV, more or less. There's not a whole lot of fiddling.

A network cable is more like an antenna cable. If you plug it in and see nothing, maybe you're on the wrong channel, band, protocol.... It can carry lots of different things at the same time, you have to select what you want.

This is why you can't just 'cat /dev/ethernetdevice' and see the raw data from your data logger. You need to know what IP address and protocol you want to get data from, and have to have your computer configured correctly to read it.

Is there a way it's supposed to be used? Absolutely but we don't know what it is yet since all the information we need to know is missing. You've refused to answer all our questions.

You've been asked repeatedly for information about the device you're trying to log from. What is it? What model is it? Chances are the device will not log information until you make a TCP connection to it. It might use telnet or it might use http or it might use something else. The information may be in its manual.

When you tried to make a network, presumably to talk to this device on, we asked you repeatedly what information you had for the various things on your network. Several working, cooperating pieces all correctly configured are are required for a working network; knowing one computer's settings is less than half the story.

Moderator's Comments:

We cannot help you if you don't start answering questions. We are not being mean. These questions are essential.

I already wrote a program using your advice last week to log the Ethernet (TCP) data. Works fine. Thanks for the help. I opened a socket and connecte to the instruments IP and Port (as provided by manufacturer). Packet data is logged to MicroSD.

Given my new knowledge of these different data trasmition protocols I was just wondering how these Ethernet->USB devices work that's all.

Sorry for being a pain.

The lack of feedback on your topics, and your fixation on turning eth0 into a ttyUSB device, gives the impression you're still fighting the same problem.

USB ethernet adaptors are nothing less than an external network "card". It will act just like your other ethernet devices. It will not make a TTY device. How could it? It's not going to have the correct port for your data logger built into the hardware.

There may be a raw USB device to read, but its data won't make much sense to you unless you spend some years studying USB protocol and reverse-engineering your USB network card's driver.

Okay, so the card would just have its own IP and port of transmission then?

Yes, it'd need an IP address to talk over an IP network just like your other ethernet devices.

The "port" has more to do with the program you're connecting with. Consider it like a telephone branch office. The IP address is the "building", the port is the "extension number". Opening 1.2.3.4 port 80 would get you its web server, 1.2.3.4 port 21 would get its ssh server, etc.

Does your data logging program absolutely require a serial port? You might be able to emulate that, running an external program to read from TCP/IP and write to a pretend serial device, or perhaps a FIFO.