[Tinyos-help] Precise contents and length of the 802.15.4 frames (and most especially with the TestNetwork App)

[Tsung-Han Lin]

No the radio stack supports variable packet length.
The packet length is determined by the length field in TOS_MSG.

TOSH_DATA_LENGTH only determines the limit of your payload size.

-Han

roberto pagliari 提到:
> I think the module CC2420RadioM send a payload (excluding headers and 
> footers) of TOSH_DATA_LENGTH, regardless of the particular size of your 
> message. the only way is to change the TOSH_DATA_LENGTH definition 
> within ..\micaz\AM.h
> 
>       pMsg->fcflo = CC2420_DEF_FCF_LO;
>       if (bAckEnable)
>         pMsg->fcfhi = CC2420_DEF_FCF_HI_ACK;
>       else
>         pMsg->fcfhi = CC2420_DEF_FCF_HI;
>       // destination PAN is broadcast
>       pMsg->destpan = TOS_BCAST_ADDR;
>       // adjust the destination address to be in the right byte order
>       pMsg->addr = toLSB16(pMsg->addr);
>       // adjust the data length to now include the full packet length
>       pMsg->length = pMsg->length + MSG_HEADER_SIZE + MSG_FOOTER_SIZE;
>       // keep the DSN increasing for ACK recognition
>       pMsg->dsn = ++currentDSN;
>       // FCS bytes generated by CC2420
>       txlength = pMsg->length - MSG_FOOTER_SIZE; 
>       txbufptr = pMsg;
> 
> txbufptr is the pointer to the TOS_Msg to be transmitted, but within 
> TOS_Msg a uint8_t buffer of TOSH_DATA_LENGTH size is defined.
> 
> On 7/3/07, * Philip Levis* <pal at cs.stanford.edu 
> <mailto:pal at cs.stanford.edu>> wrote:
> 
>     On Jul 3, 2007, at 2:10 PM, John Griessen wrote:
> 
>      > Steve McKown wrote:
>      >> 3 - If it's not.. what use does it have?
>      >>
>      >
>      > The metadata is useful for writing network functionality.  It's
>      > used in CTP for example, to manage neighbors and routing.  I don't
>      > think you'd want an application to use metadata directly, since
>      > you're then tying that application to a specific bit of radio
>      > hardware.
>      >
>      >
>      > So timestamp metadata should go in a component or an interface?
>      >
>      > Has anyone found the most accurate way to deterministically
>      > clock the arrival of a timing packet, that can be recognized
>      > without decoding,
>      > since its data content never varies?   (The application I have in
>      > mind is precise timestamping.)   Is there any physical output of
>      > the radio for the
>      > timing of a received packet as the radio locks onto its data
>      > transitions, or
>      > is packet timing and recognizing  all internal and a RX ready
>      > interrupt is the earliest
>      > output?
> 
>     Take a look at the RadioTimeStamping interface. Some radio stacks
>     issue an event on the first data bit of a packet, right after the
>     preamble.
> 
>     Phil
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