By looking at the source code, I found CC2420 does not do address decoding. The code is as below (in CC2420ReceiveP.nc):
async event void RXFIFO.readDone( uint8_t* rx_buf, uint8_t rx_len, error_t error ) {
...
async event void RXFIFO.readDone( uint8_t* rx_buf, uint8_t rx_len, error_t error ) {
...
// pass packet up if crc is good
if ( ( buf[ length ] >> 7 ) && rx_buf ) {
uint8_t type = ( header->fcf >> IEEE154_FCF_FRAME_TYPE ) & 7;
signal CC2420Receive.receive ( type, m_p_rx_buf );
if ( type == IEEE154_TYPE_DATA ) {
post receiveDone_task();
return;
}
...
if ( ( buf[ length ] >> 7 ) && rx_buf ) {
uint8_t type = ( header->fcf >> IEEE154_FCF_FRAME_TYPE ) & 7;
signal CC2420Receive.receive ( type, m_p_rx_buf );
if ( type == IEEE154_TYPE_DATA ) {
post receiveDone_task();
return;
}
...
}
This shows that CC2420 stack forwards all messages to upper layers without decoding addresses.
I am really confused. :(
Tie
On 10/29/06, Ryan Stinnett <[EMAIL PROTECTED]> wrote:
T2's CC2420 radio stack uses the radio's automatic ACK feature, which
requires its address decoding feature as well. The software radio stack
supports snooping in that it will pass you packets for which you are not
the destination if it gets them from the radio. However, the default
radio configuration does not pass the packets to software at all. What
you need to do is disable the CC2420's address decoding. Unfortunately,
I haven't tried to do this in T2 yet, so I'm not sure how it would be
done. For more information, look at the CC2420 datasheet on Chipcon's
website.
- Ryan Stinnett
"Tie Luo" <[EMAIL PROTECTED]> wrote:
>From the last email it appears that CC2420 does provide snooping
functionality, doesn't it? If unfortunately, it does not, then how to
snoop on micaz? Synchronous ACK is not necessary to us. Really need
help. Thanks a lot. Tie On 10/28/06, Tie Luo <[EMAIL PROTECTED]> wrote:
> >
> > Thanks.
> > But in CC2420ActiveMessageC, Snoop is wired to
CC2420ActiveMessageP.snoop,
> > and in CC2420ActiveMessageP, it has the following code:
> > event message_t* SubReceive.receive(message_t* msg, void* payload,
uint8_t
> > len) {
> > if (call AMPacket.isForMe(msg)) {
> > return signal Receive.receive[call AMPacket.type(msg)](msg,
payload,
> > len - CC2420_SIZE);
> > }
> > else {
> > return signal Snoop.receive[call AMPacket.type(msg)](msg,
payload,
> > len - CC2420_SIZE);
> > }
> > }
> > where SubReceive is finally wired to CC2420ReceiveP.receive.
> > In CC2420ReceiveP, it has the following code:
> > if ( type == IEEE154_TYPE_DATA ) {
> > post receiveDone_task();
> > return;
> > }
> > and in receiveDone_task(), Receive.receive is signaled.
> >
> > All the above means that, no component seems to check the destination
> > address unless CC2420ActiveMessageP. But this component does signal
> > Snoop.Receive().
> >
> > So, why CC2420 is not able to snoop? And, I indeed do not need
synchronous
> > ACKs.
> >
> > Tie
> >
> > On 10/28/06, Philip Levis < [EMAIL PROTECTED]> wrote:
>> > >
>> > > On Oct 27, 2006, at 10:13 PM, Tie Luo wrote:
>> > >
>>> > > > Dear all,
>>> > > >
>>> > > > I am using AMSnoopingReceiverC, but the node seems only receive
>>> > > > message destined to the node itself, and cannot receive messages
>>> > > > for others.
>>> > > > I saw in CC2420ActiveMessageC.nc there is a comment:
>>> > > > "Note that snooping may not work, due to CC2420 early packet
>>> > > > rejection if acknowledgements are enabled."
>>> > > > However when I check all relevant files like CC2420CsmaC.nc,
>>> > > > CC2420CsmaP.nc, CC2420ReceiveC.nc , CC2420ReceiveP.nc, it appears
>>> > > > that the snooping function does get fulfilled.
>>> > > >
>>> > > > So, does AMSnoopingReceiver really work on micaz? (TinyOS 2.x)
>>> > > >
>>> > > > Dr. Levis, you wrote that comment, may you help on this question?
>>> > > > Many thanks!
>>> > > >
>> > >
>> > > You cannot snoop with the default T2 CC2420 stack. If you want to
>> > > snoop you have to disabled address decode, which means you do
not get
>> > > synchronous acks.
>> > >
>> > > Phil
>> > >
>> > >
> >
> >
> > --
> > Regards,
> > Tie
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--
Regards,
Tie
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