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* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> 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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