JN516X Datasheet, PDF (30/94 Pages) NXP Semiconductors – IEEE802.15.4 Wireless Microcontroller

8.3 Baseband Processor
The baseband processor provides all time-critical functions of the IEEE802.15.4 MAC layer. Dedicated hardware
guarantees air interface timing is precise. The MAC layer hardware/software partitioning, enables software to
implement the sequencing of events required by the protocol and to schedule timed events with millisecond
resolution, and the hardware to implement specific events with microsecond timing resolution. The protocol software
layer performs the higher-layer aspects of the protocol, sending management and data messages between endpoint
and coordinator nodes, using the services provided by the baseband processor.
TX
Stream
Append
Checksum
Serialiser
Status
DMA
Engine
Supervisor
Radio
Protocol Timing Engine
CSMA
CCA
Backoff
Control
RX
Stream
Verify
Checksum
Control
Deserialiser
Protocol
Timers
Security Coprocessor
AES
Codec
Encrypt
Port
Decrypt
Port
Figure 19: Baseband Processor
Processor
Bus
8.3.1 Transmit
A transmission is performed by software writing the data to be transferred into the Tx Frame Buffer in RAM, together
with parameters such as the destination address and the number of retries allowed, and programming one of the
protocol timers to indicate the time at which the frame is to be sent. This time will be determined by the software
tracking the higher-layer aspects of the protocol such as superframe timing and slot boundaries. Once the packet is
prepared and protocol timer set, the supervisor block controls the transmission. When the scheduled time arrives,
the supervisor controls the sequencing of the radio and modem to perform the type of transmission required, fetching
the packet data directly from RAM. It can perform all the algorithms required by IEEE802.15.4 such as CSMA/CA
without processor intervention including retries and random backoffs.
When the transmission begins, the header of the frame is constructed from the parameters programmed by the
software and sent with the frame data through the serialiser to the Modem. At the same time, the radio is prepared
for transmission. During the passage of the bitstream to the modem, it passes through a CRC checksum generator
that calculates the checksum on-the-fly, and appends it to the end of the frame.
8.3.2 Reception
During reception, the radio is set to receive on a particular channel. On receipt of data from the modem, the frame is
directed into the Rx Frame Buffer in RAM where both header and frame data can be read by the protocol software.
An interrupt may be provided on receipt of the frame header. As the frame data is being received from the modem it
is passed through a checksum generator; at the end of the reception the checksum result is compared with the
checksum at the end of the message to ensure that the data has been received correctly. An interrupt may be
provided to indicate successful packet reception. During reception, the modem determines the Link Quality, which is
made available at the end of the reception as part of the requirements of IEEE802.15.4.
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JN-DS-JN516x v1.1 Production
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