Have read the datasheet, got it. Thanks.
But why SpiPacket.send use 'uint16_t length' as its parameter, since zigbee only allow 127 byte packets?
On 9/29/06, Jonathan Hui <[EMAIL PROTECTED]> wrote:
This is explained very clearly (with figures) on pages 38 and 39 of
the CC2420 datasheet.
http://focus.ti.com/lit/ds/symlink/cc2420.pdf
--
Jonathan Hui
[EMAIL PROTECTED]
On 9/28/06, Tie Luo <[EMAIL PROTECTED] > wrote:
> Dr Hui, at first I thank you very much for your explanation.
> Based on your answer to 1.2, buf[ length ] is crc. But why buf[ length ]
> >> 7 being one indicates a good crc?
>
>
>
> On 9/28/06, Jonathan Hui <[EMAIL PROTECTED]> wrote:
> > On 9/28/06, Tie Luo <[EMAIL PROTECTED]> wrote:
> > > 1) CC2420ReceiveP.nc , in event void RXFIFO.readDone(uint8_t* rx_buf,
> uint8_t
> > > rx_len, error_t error )
> > > 1.1) line 197:
> > > if ( length > 10 ) {...} (where length is header[0])
> > > Q: why use constant 10? Does it mean sizeof(cc2420_header_t)? If
> so,
> > > will it always be true, since length include a 11-byte header and a
> payload?
> >
> > This is simply for timestamping information. The CC2420 is doing
> > hardware address rejection, so any packets that are rejected should
> > not be considered.
> >
> > > 1.2 ) line 207,208:
> > > // pass packet up if crc is good
> > > if ( ( buf[ length ] >> 7 ) && rx_buf ) {...}
> > > Q: buf[ length ] is the byte beyond the last byte of
> header+payload,
> > > so why judge on that? and what does it being shift by 7 bits mean? How
> does
> > > this related to crc (see the comment above)
> >
> > The crc comes after the payload. Please see the CC2420 datasheet.
> >
> > > 2) in message_t, length=header+payload+footer, right? But in
> > > CC2420TransmitP.nc line 243 is:
> > > call TXFIFO.write( (uint8_t*)header, header->length - 1 );
> > > Q: why -1?
> >
> > The length byte is not included in the length of the packet. Please
> > see the 802.15.4 spec.
> >
> > > 3) related to (2), in the same file at line 421: msg_metadata->rssi =
> > > ack_buf[ length - 1 ]; while rssi is define as the 2nd field of
> > > typedef nx_struct cc2420_metadata_t {
> > > nx_uint8_t tx_power;
> > > nx_uint8_t rssi;
> > > nx_uint8_t lqi;
> > > nx_bool crc;
> > > nx_bool ack;
> > > nx_uint16_t time;
> > > } cc2420_metadata_t;
> > > So why ack_buf[ length - 1 ] is rssi?
> >
> > The crc is replaced with rssi when in auto crc mode. Please see the
> > CC2420 datasheet.
> >
> > > These questions really make us blue, can you help us out? Thanks a ton!
> >
> > If not obvious already, I *strongly* recommend that you read the
> > CC2420 datasheet and the 802.15.4 spec. They will clear a lot of these
> > issues up.
> >
> > http://www-s.ti.com/sc/ds/cc2420.pdf
> >
> http://standards.ieee.org/getieee802/download/802.15.4-2003.pdf
> >
> > --
> > Jonathan Hui
> > [EMAIL PROTECTED]
> >
>
>
>
> --
> Regards,
> Tie
> _______________________________________________
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> [email protected]
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>
>
>
--
Regards,
Tie
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