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The Atmel AT90USB1268 Microcontroller essentially serves as the 'brain' of the smart packet radio and performs a variety of functions to ensure the radio operates correctly. The microcontroller, or MCU, is responsible for interfacing the external control terminal with the smart packet radio's on-board transceiver module. This is achieved through the use of a serial peripheral interface, or SPI, available on the chip and the LUFA library. The MCU is also responsible for formatting and decoding packets arriving at the radio as well as gathering statistics which may be useful to the host controller.

In order to properly interface with the control terminal, the MCU utilises the LUFA library, which causes the MCU to appear as a serial communication port when it is plugged into a USB port of a PC. This enables easy access to the MCU across most platforms through the use of their serial libraries. At this time, the host terminal passes an instruction packet to the MCU through the SPI, which is then translated by the MCU into an action to be performed by the board. The MCU also uses the SPI to return received packets and statistics data to the host terminal, which can then be used in higher layer operations.

The MCU, depending on the configuration, can also control the SPR's link layer functions. So far we have implemented an Aloha-inspired, and CSMA inspired MAC sublayer functions that can be selected by sending a control packet to the SPR. These MAC implementations allow the board to send and receive acknowledgement messages (ACKs) as well as control a retransmission scheme without the need for instructions. When one of these modes is enabled, the MCU also collects statistics about the number of retransmissions and the time for a given packet to be acknowledged.

While the MCU is used mainly for the communications part of the radio, it also performs a number of other functions. Ports A and D are connected to external headers, which can be utilised as general input/output pins, while Port B is connected to a number of LEDs which can be programmed to show the status of the radio. Of particular note is a blue LED positioned on the board opposite the antenna, which is set to blink at a constant rate to denote the microcontroller is functioning as expected.

Topic revision: r6 - 2014-05-02 - AhmetSekercioglu
 
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