reading the usb

Depends on the OS -- what OS is it?

You probably won't be able to find out whether the device is connected just by looking at /dev/ttyUSB*. You might be able to get stats on what USB devices are connected and figure out what ttys they're bound to, but this is bound to be complicated.

You could maybe just send out an are-you-there and see if you get anything back ..

--mpa

Hi,

The operating sytem is Linux.

I would poke around /proc. That is where linux puts status type information. I don't have my Linux box close, or I could tell you where in /proc to look.

eepoke

What I do is set up udev rules to name the USB devices consistently regardless of the order they're plugged in.

/proc/bus/usb/devices

Yep, that would seem to be the "right" answer to the OP's problem.

mary, you seem to be further than i in this kind of job could you (or anyone else, for that matter) give me some pointers as to the the beginning? does one do an fopen on the right /dev entry, then freadc or the like?

I did search google but only got a bewildering multitude of non-useful results. sincere apologies if I'm considered too lazy or off topic... karel

Some pointers:

thank you sir, that's a most useable reply! (though i had hoped for an example, or a link to one...) KA

The Posix Serial Programming Guide has tons of examples.

it has indeed, and a nice website it makes! but the word USB does not once figure in it, or i should have overlooked it it's all about rs-232 as far as i can see.

maybe my question should have been: "i might be able to figure this out for rs-232 but are there any differences for USB serial apart from the device to open?"

I thought you were using a USBRS-232 serial widget.

RS-232 is the standard which defines the 25-pin D connectors and electrical signalling levels at those connectors. It's got nothing to do with the UART or how that UART is attached to the CPU.

No, there are no differences in the serial port API between ISA-attached serial ports and USB-attached (or Ethernet-attached, for that matter) serial ports. That's what device drivers are for, you know. ;)

There are going to be differences in timing. For example: when you make the call to set RTS, that happens immediately for ISA-bus and PCI-bus attached devices (by "immediately" I mean that you know that when the ioctl() system call returns, you know the operation has been completed and the RTS line is in the requested state). It doesn't happen immediately for USB. The ioctl() call may just queue up a request to set RTS. The ioctl() call can return before the USB host controller has sent the request.

Oh, unless you're a glutton for punishment, I wouldn't actually recommend using C at all for host-side serial apps. I use Python and the pyserial module for 99% of my serial stuff. Apart from taking a fraction of the time to develop when compared to C, the resulting program will work under Linux/Unix, Windows, MacOS, and Java VM.

yes. also, my linux (suse 8.2) has a utility called lsusb which consults the same information.

I am in a similar config and have found that, during the boottime hardware scan, a line is added to /var/log/messages stating the ttyUSB# used. KA

Well yes, in a way I am, but it seems to me my config is the reverse of what you figured.

Actually, I want to read GPS-data from a Hicom receiver that has a 6-pin DIN-connector, like on pre-USB PC keyboards. It sends out a continuous stream of GPS-data at 4800,n,8,1 which I can perfectly receive and decode. But it also has a convertor from the DIN-connector to USB, and is recognized by the Linux box; only I seem unable to read any data from it.

NB the reason I should like to read from USB is that serial ports are less and less common on PC's and especially on portables.

Thanks for your interest! KA

I assumed you have a USB-serial adapter where the USB end plugs into the Linux host and the serial end plugs into some device or other. If that's not what you're talking about, then for pete's sake tell me what you _are_ talking about rather than making us guess.

That's exactly what I was talking about.

What's it recognized as? I'd be surprised if it's not either a PL2303 or an FTDI USB-serial adapter. From what I've seen 95% of the USB serial converters are one or the other. There are about a 20 other USB-serial adapters supported by Linux, but I've never seen any of them in use.

And I've given you pointers for documentation on exactly how to do it.