[BRLTTY] introduction and a problem

[lutz kaiser]

Hi Dave and list,

thanks for your answer.

no, my hardware was not changed. I use this Laptop (dell inspiron 1501) 
since 2007 together with this adapter.

This adapter is an Ftdi.

The problem occured when updating my debian system a week ago. I can't 
exaclty say when.


The only thing i can think of, is my setting for cups, i setted it up to 
use my usb Printer, but this cannon Mp150 is also an elder device here.
Better i did dpkg-reconfigure cups; and selected usb, ? ... but i dont 
beliefe that this caused anything bad.


thank you for reading, If ever i can help with informations, testing - i 
'll do.

kind regards
Lutz
ps: debian unstable
brltty version 4.3dev revision 5246
usb Keyboard , external Harddisc, cannon printer, mouse
and off course ftdi usb2serial adapter


Am 06.08.2010 16:23, schrieb Dave Mielke:
> [quoted lines by lutz kaiser on 2010/08/06 at 11:08 +0200]
>
>> i found  a better way:
>> some seconds after starting brltty
>> echo \002\033b>/dev/ttyUSB0
>
> I now understand what's going on. It's a problem we're actually familiar with
> whenever a device is connected via USB. Since the CombiBraille uses serial I/O,
> I didn't recognize what was going on until I realized that you're using a USB
> to serial adapter.
>
> As part of USB communications, there's what amounts to a flag which is commonly
> called the endpoint data toggle. It has to be in the same state on both the
> host and the device else data isn't transferred. For reasons that I don't
> understand, whenever we open a USB device on Linux there's a seemingly high
> probability (perhaps 50%) that the data toggle is out of sync. All of our
> drivers which support direct USB I/O silently hide this problem by trying up to
> three times to get a response from the device. I guess there's also a risk of
> this problem occurring for serial devices if a USB to serial adapter is being
> used.
>
> Am I correct in understanding that this problem didn't used to happen to you?
> Can you remember what change in your system or way of doing things caused it to
> start happening? Is it, perhaps, that you used to use a direct serial
> connection, and that the problem started occurring when you started to use the
> adapter?
>

-- 
viele Grüße
Lutz