[BRLTTY] introduction and a problem

[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?

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Dave Mielke           | 2213 Fox Crescent | The Bible is the very Word of God.
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