Attached a USB device and have a question!

[virrick]

Hello everyone!

Totally new to FreeBSD and I have a question.

I attached a hydrabus that I usually connect to with picocom on other systems. I ran dmesg to get the TTY it was running on so I could connect. dmesg said it was at usbus0. I looked in /dev and didn't see usbus0. In order to compare the /dev directory I ran a ls with the device attached and not attached and piped the output of each to different files. I diffed the files and noticed there were a few differences most notably a ttyU0. I gave it a go and was able to connect!

My question is why was the tty different than what dmesg said. Again I'm totally new to FreeBSD(just got it installed today!) and I assume there is something I'm not understanding about how FreeBSD works.

Here is a few screen shots. I hope they look ok. Still testing things out!

 

[ralphbsz]

USB is complicated (as are most other interfaces). Internally in the computer, there are likely a variety of USB interfaces, which then have layers. The FreeBSD host knows all of those, and gives them names. But you can't talk to an interface, only to a device plugged into an interface. The fact that "the USB hole at the top left of my laptop, which has a USB hub plugged into it, and then the 3rd USB port from the top of that hub" has a name which is visible in places like dmesg or the output of usbconfig doesn't mean that it deserves a /dev/ entry for a device that one can do something with.

So there is a whole hierarchy of usbus and ugen entries that are visible in dmesg but don't show up in /dev/. I just looked on my server, and there are three USB things attached: A keyboard (shows up as /dev/uhid0), a modem (shows up as /dev/ttyU0), and a hard disk (shows up as /dev/da0, all other disks are /dev/adaX). To be honest, I can't remember how to exactly map from ugen8.2 to /dev/ttyU0 and back; the output from the usbconfig utility shows an enormous amount of information, but not the mapping to the device entry that is created, nor does dmesg.

 

[virrick]

Great information in your response! I have learned a lot of new things by your response after some good research.

1: ugen is like a generic USB driver if there is no special driver for the USB device.
2: Not all devices deserve a entry in /dev/(if Im understanding correctly).
3: The basics of usbconfig and how to use it.
4: Each USB controller gets assigned a name like usbus0.
5: There is a naming convention for /dev/ devices.

Good stuff! Thanks again for the reply. I learned a lot.