On Sun, Aug 28, 2011 at 12:41 AM, Chieh-Jan (Mike) Liang <[email protected]
> wrote:
> I believe the check is there to make sure software ACK mimic CC2420's
> hardware ACK, because CC2420 acks broadcast packets (if requested).
>
And does the h/w (cc2420) also just look at the DSN too? This seems
broken.
>
> Mike
>
> On Aug 27, 2011, at 3:04 AM, Xiaohui Liu wrote:
>
> > Hi everyone,
> >
> > Why should broadcast be acknowledged? If multiple recipients receive a
> broadcast packet, they will ack it at very close time instant, which can
> cause ack collision. But the following snippet is found in CC2420ReceiveP.
> Can anyone help me understand why broadcast can be acked? Thanks.
> >
> > if(call CC2420Config.isAutoAckEnabled() && !call
> CC2420Config.isHwAutoAckDefault()) {
> > if (((( header->fcf >> IEEE154_FCF_ACK_REQ ) & 0x01) == 1)
> > && ((header->dest == call CC2420Config.getShortAddr())
> > || (header->dest == AM_BROADCAST_ADDR))
> > && ((( header->fcf >> IEEE154_FCF_FRAME_TYPE ) & 7) ==
> IEEE154_TYPE_DATA)) {
> > // CSn flippage cuts off our FIFO; SACK and begin reading again
> > call CSN.set();
> > call CSN.clr();
> > call SACK.strobe();
> > call CSN.set();
> > call CSN.clr();
> > call RXFIFO.beginRead(buf + 1 + SACK_HEADER_LENGTH,
> > rxFrameLength - SACK_HEADER_LENGTH);
> > return;
> > }
> > }
> >
> > --
> > -Xiaohui Liu
> > _______________________________________________
> > Tinyos-help mailing list
> > [email protected]
> > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
>
>
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--
Eric B. Decker
Senior (over 50 :-) Researcher
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