[BRLTTY] USB and serial/USB converter

[Mario Lang]

Samuel Thibault <samuel.thibault at ens-lyon.org> writes:

> There is quite often some confusion between -d usb: and
> -d serial:ttyUSB0, and it is not necessarily obvious for the beginners
> to understand the difference between both.

This is the same on other operating systems.  In fact, to configure
a USB device on Windows means assigning a more or less random
serial port to your converter, and using that COM port in your screen reader.
People have to learn the differences everywhere.

> Would it be ok to have usb: also try serial:ttyUSB0?  It looks like
> it could help a lot of people to easily get started with brltty.

I have to say, my gut reaction is that I am against such a change.
It looks like it needlessly complicates things.

There is a very simple way to achieve what you want, setting
device to default to "usb:,serial:ttyUSB0".  But if you look at it,
would you really want to have that as a default?  It looks very
arbitrary.  Besides, most serial drivers still dont support
autodetection, so while you might be able reduce the amount of
configuration on the users end a little bit, you will also
create new problems, since "-b all" will not work with all
serial devices...  There is a third potential problem with that, some
of our natively supported USB braille devices do in fact
work like a USB-to-serial adaptor internally, and will be recognized
by the Linux kernel.  So if you open /dev/ttyUSB0 first, you
will end up using the device via the kernel USB-to-serial adaptor driver,
not via the native brltty USB implementation.  While this probably
still works, it looks like another source of potential bugs hard to find.

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