Jean Tourrilhes <[EMAIL PROTECTED]> writes:
> Hi,
>
> As Belkin doesn't seem interested in answering me, I think I
> will have to buy some other dongle...
>
> From US, it's quite easy to buy an Actisys or a JetEye, and
> there are approx the same price. Puma/Tekram seems a bit more
> expensive, and LiteLink (if it still exist) is physically too big.
> Now, I had a look at the driver to see the capability of the
> drivers. These are my conclusions :
> o esi.c : only 3 speeds possible, turnaround 10ms
> o litelink.c : seems really good on everything
> o actisys.c : 40 ms to move from one speed to the next
> o tekram.c : 100 ms to set speed, 10ms turnaround
> I believe that having many speed doesn't matter much, because
> 115kb/s is almost as reliable as 9.6kb/s, so as long as you do 9.6kb/s
> and 115kb/s you are ok.
Not with the Palm Pilot (see below)
> On the other hand, time to change speed is important, because
> latency is already an issue, especially if you do lot's of small
> transfer (like using IrObex). Having n x 40 ms or 100 ms dead time
> before each transfer seems to me some undue overhead (it's 1.4 kB at
> 115 kb/s). The same for a 10ms turnaround...
> On the other hand, maybe I misread the drivers and that those
> values are us (which would fit my hardware assumptions), or maybe
> there is so many other latencies issues in the IrDA stack that in fact
> it doesn't matter...
>
> So, could anybody comment on the dongle performance ?
Well, here is some thoughts about dongle speed:
1) Even though a dongle can change speed fast, the peer device may still
use 200 milliseconds or more to change its speed. So changing the speed
fast may not help anything. So if you change the speed fast, then the peer
device may miss the first RR frame, which means that you must retry after
some timeout which will make it all take _much_ longer time, than if you
had used longer time to change speed ;-)
2) Minimum turnaround time has a big impact on performance, and the
impl. is usually using the value from the documentation for the dongle. I
guess that I have sometimes just picked a (safe) value, since using 0 ms is
not a good idea. A longer mtt will however give you better range, but worse
throughput. When making Linux-IrDA I must try to be sure that the settings
works for most people, so they may not be optimal. You should however
experiment with the mtt and find the lowest mtt that works for your
equipment (I usually set it to 0 myself when I need good speed ;-) Notice
that a low mtt might work for one device, but not for another (which is why
I have to be on the safe side in the versions I distribute)
3) The JetEye is probably the most stable dongle because the impl. is so
simple, but the JetEye doesn't support 57600 which is used by the Palm
Pilot, so it you use the JetEye with the Palm you will only get 19200
bps. One other thing with this dongle is that the cable is not very well
attached to the dongle, so the cable will slip out after some weeks and
expose the wires inside :-(
4) The Girbil dosn't do echo-cancellation which means that you must use
irport with this dongle. The girbil is however the nicest and smallest
dongle ;-) I have had some problems with my impl. of this dongle, but they
may be fixed now in the new dongle arch.
5) The Tekram dongle is quite large, but it's working very nice (at least
with the patches I made today ;-) It supports most speeds, and also
TV-remote mode I think.
6) The LiteLink dongle is quite big, but the impl. is also quite simple so
it should be stable to use (at least with the very latest patches ;-)
7) Although I have written the driver for the ACTiSYS dongle, I don't have
it :-( So I cannot tell you anything about this dongle.
Hope this will make it easier for you to choose a dongle.
DISCLAIMER: Any dongle problems listed above may be problems with
Linux-IrDA and not with the dongle itself. I have just tried to tell you
how this dongle works with Linux-IrDA (it might work better with Windows).
-- Dag
--
/ Dag Brattli | The Linux-IrDA Project /
// University of Tromsoe, Norway | Infrared communication for Linux //
/// http://www.cs.uit.no/~dagb | http://www.cs.uit.no/linux-irda/ ///
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