Linux uses vendor and product id as well, but there is wildcard
matching, so the driver is loaded based on the match. Linux has a more
flexible architecture for USB hotplug, so it is up to the distribution
or the upstream provider of the USB system to decide what driver to
load, not the manufacturer of the peripheral. Also, in Windows, what is
called the "driver" is often a driver and an application program to be
autorun when the device is detected. For RS232 dongles, there is no
application program, but for some device that happens to incorporate the
same chip but wants to autolaunch an app, there is.
For example, the Vector Network Analyzer from Mini Radio Solutions uses
such a chip to provide USB connectivity, although it is inherently a
serial device. When I plug it in to Windows, it uses a generic driver I
had to manually install, and it maps the device to some random COM port,
using a number that changes from time to time; sometimes it is COM11,
sometimes COM13. I have to find the init file for the VNA software and
edit it.
When I plug it in to Linux, it gets assigned the next device number, and
for some reason it seems stable, so I can leave the init file set as
/dev/ttyUSB1. (My K2 is on hardware RS232 port /dev/ttyS0 and my
antenna controller on /dev/ttyUSB0). If the MiniRadioSolutions people
had gone all out, they could have gotten a special id and written
something that runs their Visual Basic program automatically, but then
upgrading it would have been a constant pain for hams who want to change
it or try out other versions. Still, not having to look for the COM
port would have been nice, and that is mainly what the USB driver system
in Windows tries to solve with its id system. The price we all pay,
though, is a complete failure for generic devices such as RS232
converters.
When I put an SD card from my camera into my Linux box, it notices it,
finds that it has a Win32 DOS filesystem on it, finds the driver, and
mounts it as a filesystem. Thw Gnome window system I run at home then
notices the mounted filesystem, susses out the directory structure and
guesses that is is from a camera (and not a USB memory stick for files
or an MP3 player) and offers to start a photo edit/drag-and-drop tool.
No manufacturer of camera or SD card was involved. (I suspect the Mac
does the same thing, only in a more refined way and with prettier
icons.)
73,
Leigh/WA5ZNU
On Mon, 7 May 2007 1:41 pm, James austin wrote:
Windows loads USB drivers based on the vendor id and product id
reported by the device. Are you implying that MacOS and Linux do it
differently, by saying the driver used is based on the chip?
73,
Jim
So, getting USB to work depends on the following:
1. the chip(s) implementing the USB port in your computer;
2. the driver for the chip implementing the USB port in your computer;
3. the chip(s) implementing the serial-to-USB adaptor;
4. the driver provided with the serial-to-USB adaptor.
If you are using a MacOS, Linux, or a flavor of UNIX you will find
that there tend to be only a few generic drivers for this since the
drivers are based on the chip(s) used. Windows requires a vendor-
specific driver for each device. The latter means that even if you
get the same hardware (serial-to-USB converter) from two different
vendors (generic Taiwanese serial-to-USB adaptor), you need two
different drivers for Windows but only one generic driver with MacOS,
Linux, or *NIX.
73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com
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