Dag wrote :
>
> On Mon, 1 Oct 2001 10:48:51 -0700, Jean Tourrilhes wrote:
> > ------------------------------------------
> > A USB IrDA Bridge device uses two bulk endpoints (one in and one out)
> > to exchange IrLAP frames between the host and an IrDA device. Thus,
> > the half duplex IrLAP protocol is actually transmitted over what
> > appears to be a full duplex communications channel. Due to this fact,
> > the USB IrDA Bridge device optimizes turn-around time between itself
> > and the IrDA device. IrLAP frames are exchanged based on USB bus
> > availability rather than forcing the USB driver client to track IrDA
> > device turn-around time.
> > ------------------------------------------
>
> The text only tries to tell you that you don't have to keep
> track of the current direction (turnaround) of the IrDA hardware
> as you have to do with other IrDA FIR chipsets where you
> explicitly have to tell if the hardware should be in Tx or Rx
> mode. You must however keep track of *when* to do the
> turnarounds yourself.
Well, that's a way to look at it. However, the text
specifically talk about "time", not about "mode". And if it says
"time", it must be something related to timing, I guess.
> > To me, it is beyond my imagination to *NOT* do the turnaround
> > in the dongle. It just make so much sense...
>
> No, because most stacks (including Linux-IrDA) optimizes the
> turnaround time, and will give away the token right away it if
> doesn't have anything data to send, and then back off if both
> sides doesn't have anything to send (FastRR's). Remember that
> the IrDA link doesn't turnaround at a fixed rate!! It's only a
> lower and upper bound. Even the stack doesn't know if or when
> it's going to send a frame. It only tries to make sure it
> doesn't happen before or after the min and max turn times.
Ok, let me correct myself :
"To me, it is beyond my imagination to *NOT* do the MIN
turnaround in the dongle."
Of course, the MAX turnaround is handled by IrLAP and based on
totally different considerations, and in fact totally unrelated to the
MIN turnaround time. If stack doesn't send anything to the dongle, I don't see how it
could go in transmit mode (let's be realistic here ;-).
> [...]
>
> I agree that the dongle could help with handlingq the min.
> turnaround, and many other FIR chipsets does this. But it
> shouldn't do it automagically, since that would be
> over-engineering. Provice mechanisms, not policies!! They should
> be as high up in the system as possible.
Exactly. I just want the dongle to enforce the MIN turnaround
time by delaying the Tx frame if to early. The MIN turnaround should
be something that the stack set in the dongle, the same way it set the
XBOFS.
Actually, I don't want the dongle to second guess the IrDA
stack, I really want to ability to set it in the dongle.
If you think about it, there is lots of parallel between
XBOFS and MIN turnaround... Especially that you can use XBOFS to
generate some turnaround at SIR ;-)
Regards,
Jean
_______________________________________________
Linux-IrDA mailing list - [EMAIL PROTECTED]
http://www.pasta.cs.UiT.No/mailman/listinfo/linux-irda
