There is definitely a tradeoff on the message size you choose.
Especially, if you run into the situation where you start dropping
alot of packets. The larger they are, the more data you need to
resend, and the more energy you consume.
Since the CC1000 radio on the mica2 is a bit radio (i.e. each bit is
sent directly by the MCU through the radio and out on the air),
TOSH_DATA_LENGTH could theoretically be increased to 256 (the length
field is only 8 bits). The CC2420, on the other hand, is a packet
radio (i.e. the entire packet is buffered in the radio hardware itself
before being sent over the air). This means that the number of
payload bytes you send is limited to the size of the hardware buffer,
which in this case is 128 bytes. Remember though, that some of this
space is eaten up by things like the AM_ADDR of a mote, etc, so the
actual maximum size that TOSH_DATA_LENGTH can be set to for the CC2420
is slightly less than 128 depending on how many protocol specific
fields get introduced as part of the header for a packet.
Kevin
On 8/29/07, Ákos Maróy <[EMAIL PROTECTED]> wrote:
> I edited to multihop oscilloscope application to include more
> information, and I saw that there's a limit on the message payload size,
> as defined in message.h:
>
> #ifndef TOSH_DATA_LENGTH
> #define TOSH_DATA_LENGTH 28
> #endif
>
> #ifndef TOS_BCAST_ADDR
> #define TOS_BCAST_ADDR 0xFFFF
> #endif
>
> typedef nx_struct message_t {
> nx_uint8_t header[sizeof(message_header_t)];
> nx_uint8_t data[TOSH_DATA_LENGTH];
> nx_uint8_t footer[sizeof(message_footer_t)];
> nx_uint8_t metadata[sizeof(message_metadata_t)];
> } message_t;
>
>
> I wonder if it's feasable to extend the message size, and what the
> consequencies are? should one send more smaller packets instead of one
> bigger one?
>
>
> Akos
> _______________________________________________
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> [email protected]
> https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
>
--
~Kevin
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