The Internet Power Line Adapter - University of Queensland

Home Automation, Power Lines and the Internet Quenten Alick
Chapter 5
5.1 Software Implementation
This chapter will look at the software design issues that were considered for the
system. These design decisions will be looked at with reference to the
specifications in chapter three and the restrictions imposed by the hardware
chosen in chapter four.
5.2 Microprocessor Code
The first task that the code in both the client and server microprocessor must
complete is the communications with the P300 network chip. These
communications require the use of the SPI interface on the microprocessor. The
format for data that is being sent to the P300 is a command byte, and length byte
then zero or more bytes of data. A similar format is used for reading data from
the P300. Firstly a command byte is sent by the microprocessor. Then the P300
returns a length byte followed by the specified amount of data bytes.
An interrupt driven transmission is the easiest way to transmit the data. In this
format, the main body of the code initiates the transmission. Once the
transmission has started, the SPI interrupt code in the microprocessor completes
the rest of the transmission. The flowchart in figure 5-1 demonstrates the write
operation [15]. The read operation is very similar to this. The main difference is
that the microprocessor must feed in dummy data to generate a clock signal for
the P300 to transmit its data out on.
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