[BRLTTY] Inka's non-standard flow control

[Nicolas Pitre]

On Mon, 24 Apr 2006, Samuel Thibault wrote:

> Nicolas Pitre, le Sun 23 Apr 2006 13:41:42 -0400, a écrit :
> > On Sun, 23 Apr 2006, Samuel Thibault wrote:
> > 
> > > Hi,
> > > 
> > > Samuel Thibault, le Sat 22 Apr 2006 00:01:30 +0200, a écrit :
> > > > Getting back to a quite old discussion:
> > > > 
> > > > Dave Mielke, le Tue 26 Jul 2005 06:45:23 -0400, a écrit :
> > > > > [quoted lines by Samuel Thibault on 2005/07/26 at 10:15 +0200]
> > > > > >Do you have information about the non-standard flow control that
> > > > > >Inka uses ? 
> > > > > 
> > > > > Yes. The display must strobe CTS after each character sent by the PC, and the
> > > > > PC must strobe RTS after each character sent by the display.
> > > > 
> > > > How long does the strobe need to at least be?
> > > 
> > > If you don't have a precise answer right now, do you at least have a
> > > order of magnitude? (microseconds? milliseconds?)
> > > 
> > > I need this information for deciding how to implement this in Linux.
> > 
> > Do it in user space.  Please.
> 
> Why?

Because it is portable that way.

Because, frankly, I doubt the current serial maintainer will accept such 
a non standard behavior added to the kernel for only one 
"obscure" device.  And I know what I'm talking about when it comes to 
dealing with that person.

> Doesn't it need the strobe to be quite responsive?

How responsive does it need to be?

> We tried to implement the VisioBraille non-standard flow control, and it
> wasn't working because it wasn't responsive enough.

How was it implemented?

> If strobing _each
> character_ from user space is responsive enough, then fine. But I really
> doubt it will ever work at 57600bps...

Why not?  Did you try it?  Because the serial maintainer is sure to ask 
you the same question and possibly ask you to see your user space code.

Isn't the protocol working in lock state?  If so the transfer rate will 
be just as fast as the amount of CPU you can give it.  If you can 
transfer only 100 characters in 100ms so what?  It should be plenty 
functional already.

Otherwise, if it can't be done in user space, I'm afraid you'll have to 
tweak each low level serial drivers (let's say the 8250 for now) and 
frankly I'm afraid you'll be granted with a big "no no" if you don't 
have a strong case for it.


Nicolas