
84
42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
set;
By default there is no protection of the Frame Buffer against overwriting. If a frame is
received during a Frame Buffer read access of a previously received frame, the stored
data might be overwritten.
Finally the application software should check the transferred frame data integrity by a
FCS check.
The state of the radio transceiver should be changed to PLL_ON state after reception to
protect the Frame Buffer content against overwriting with new, incoming frames. This
can be achieved by writing immediately the command PLL_ON to the TRX_CMD bits of
register TRX_STATE after receiving the frame indicated by a TRX24_RX_END
interrupt.
Alternatively Dynamic Frame Buffer Protection can be used to protect received frames
Both procedures do not protect the Frame Buffer from overwriting by the application
software.
In Extended Operating Mode during TX_ARET operation (see
"TX_ARET_ON –switches to receive if an acknowledgement of a previously transmitted frame was
requested. During this period received frames are evaluated but not stored in the Frame
Buffer. This allows the radio transceiver to wait for an acknowledgement frame and
retry the frame transmission without writing the frame data to the Frame Buffer again.
A radio transceiver state change except a transition to radio transceiver SLEEP state or
a radio transceiver RESET does not affect the Frame Buffer content. The Frame Buffer
is powered off and the stored data gets lost if the radio transceiver is forced into radio
transceiver SLEEP state.
Access conflicts may occur when reading and writing data simultaneously at the two
independent ports of the Frame Buffer TX/RX BBP and Controller interface.
9.6.3.2 User accessible Frame Content
The radio transceiver supports an IEEE 802.15.4 compliant frame format as shown in
the following figure.
Figure 9-32. Transceiver Frame Structure
Preamble Sequence
SFD
PHR
(1)
Payload
LQI
(2)
FCS
0
4
5
6
y + 3
y + 5
y + 6
Frame
Access
SHR not accesible
RX: Frame Buffer content
PHY generated
Length [octets]
Duration
4 octets / 128 s
1
y
octets / y 32 s (y <= 128)
1
TX: Frame Buffer content
Notes:
1. Stored into Frame Buffer for TX operation
2. Stored into Frame Buffer during frame reception.
A frame comprises two sections. The radio transceiver internally generated SHR field
and the user accessible part are stored in the Frame Buffer. The SHR contains the