[mc1322x] Can a Raven stick receive at 250Kb/s?

[Umberto Manzoli]

Hi Jon,
  we had some problems with the Raven stick, as its usb-to-ethernet stack
was not very smart.
The AT86RF230 from Raven sticks behaves very well. Some problems (and
delays) arise when the mac layer has to be interfaced with the fake-uip
process, in order to forward packets to and from the host pc. Moreover, you
have to notice that most of Contiki uIP stack output functions (ethernet
and/or slip and/or ppp) perform a blocking loop, while waiting for an
interrupt to signal that data transmission has terminated. Meanwhile, the
MAC could loose some frames...

Keep in mind that IEEE 802.15.4-2006 mandates for a minimum LIFS equal to 40
symbols (IEEE 802.15.4-2006 - par. 6.1.3) for the 2450MHz PHY. The 2450 MHz
PHY symbol rate shall be 62.5 ksymbol/s. (IEEE 802.15.4-2006 - par. 6.5.3.2)
(16 us x symbol).
If you use acknowledged transmission, IEEE 802.15.4-2006 - par. 7.5.1.3
shows the main concept, i.e. you have to wait about 3 ms before triggering a
transmission of new data.
In case these framing gaps are not respected, the receiver could drop some
packets, especially latest transceivers with embedded MAC accelerator, where
802.15.4 constants are sometimes burnt into silicon.

Bye,
  UM

2009/12/28 Jon Smirl <jonsmirl at gmail.com>

> Has anyone verified that the Raven stick can receive data at the full
> 250Kb/s channel speed? My new mc13224 code can transmit at the full
> 250Kb/s (minus needed framing gaps). I had to insert delay loops to
> lower it down to 190Kb/s in order to talk the the Raven sticks.
>
> You hit these speeds on fragmented packets. A maximum TCP packet turns
> into multiple back to back 802.15.4 packets. I'm using interrupts to
> overlap the construction of the fragments with their transmission to
> achieve the full 250Kb/s speed.
>
> TCP retransmission won't recover from this problem. If I blast a full
> speed fragmented packet at the Raven stick it seems to drop at least
> one packet every time. There is no way to recover other than lowering
> the TCP frame size.
>
> The Raven stick transmits fragmented packets at 134Kb/sec.
>
> --
> Jon Smirl
> jonsmirl at gmail.com
>
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