SPI Interface

The SPI interface should be as simple and clean as possible. The more efficient the better.
At the moment the SPI protocol consists of a series of 16-bit commands comprising 8 bits of instruction and 8 bits of data.
While this works well, and is easy to code for, it is somewhat cumbersome. A better system is desirable which uses less overhead.
At the moment, to transfer 16 bits of data with an instruction takes 32 bits. It would be better to get this down to just 24 bits.
Also, some of the commands are a little long winded. As an example, to draw a filled box:
1. Set the top left X coordinate
2. Set the top left Y coordinate
3. Set the bottom right X coordinate
4. Set the bottom right Y coordinate
5. Issue the command to draw a filled box.
That is a total of 80 bits (5x16), which could just as well be represented with considerably less bits.
Some optimizations have been put in place by splitting the drawing area into 256x256 chunks and using different commands to reference different chunks, thus making all coordinate commands only 8 bit regardless of the resoution.