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m3pi preparation
Before you start using the mbed with your Pololu 3pi, you need to program the on board AVR with Pololu's "Serial Slave" example.
The easiest way is to use the binaries as described below. If you want to build your own then there are great instructions on at www.pololu.com with some handy links at m3pi-Development
The Easy Way¶
To do this the easy way you simply need to temporarily repurpose your mbed Microcontroller to be an AVR ISP programmer by using Aaron Berks mbedAVR programmer. This enables an AVR binary dragged onto mbed LocalFileSystem to be be programmed into the AVR over SPI - drag and drop programming for AVR :-)
You will need :
- m3pi AVR Programmer
- Program.zip - Contains "program.avr" - the file the ISP programmer looks for on the LocalFileSystem
Information
The mbed AVR programmer only takes .bin files currently. As the mbed microcontroller would try to load a .bin file into the mbed itself, I have opted for the .avr extension. AVR Studio generates .hex files, but there are many HEX2BIN converters available.
Setting up your hardware¶
The hardware connections between the mbed and the 3pi are simple. On the 3pi side, there is just a standard 6 way AVR ISP header :
The connection to mbed is straight forward.
| AVR ISP | mbed |
| 1 MISO | p6 |
| 2 VCC | n/c |
| 3 SCK | p7 |
| 4 MOSI | p5 |
| 5 nRST | p8 |
| 6 GND | GND |
As I am doing quite a lot of 3pi reflashing at the moment, I made myself a little breakout board on strip board, with a mbed socket and a 6 way AVR socket.