Hello all;
I would like to know the exact length of the 802.15.4 frame. The reason that
i'd like to know the exact length is because i need to do some duty cycles
numbers and one of the inputs is the frame length. It would seem to equal
the payload, but given it makes no sense to me the payload on the serial
frame, i might as well doubt i can figure the length on the 802.15.4's.
So according to TEP 125:
The TinyOS 802.15.4 T-frame format is as follows:
+-------------------+---------+------------------------------+--------------+
| 802.15.4 Header | AM type | data | 802.15.4 CRC |
+-------------------+---------+------------------------------+--------------+
I presume the 802.15.4 Header, as according to CC2420.h, to be 10 bytes:
typedef nx_struct cc2420_header_t {
nxle_uint8_t length;
nxle_uint16_t fcf;
nxle_uint8_t dsn;
nxle_uint16_t destpan;
nxle_uint16_t dest;
nxle_uint16_t src;
/** I-Frame 6LowPAN interoperability byte */
#ifdef CC2420_IFRAME_TYPE
nxle_uint8_t network;
#endif
nxle_uint8_t type;
} cc2420_header_t;
AM Type, according to previous struct, another byte before "data". Total:
11.
I suppose CRC to be 2 extra bytes added in the end. Total: 13
The "data" field intrigues me.
I see this being defined in CC2420.h
#ifndef TOSH_DATA_LENGTH
#define TOSH_DATA_LENGTH 28
#endif
Does this mean it's a fixed length that gets 'populated' according to each
different situation (making a fixed total of 42 bytes), or is 28 a max, or
am i understanding this all wrong?
The struct in TestNetwork is 15 bytes. Would that means the total frame size
is 13+15=28 bytes? Or is there anything extra added?
Any help greatly appreciated!
Thanks,
Pedro
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