Here is the Maple Mini firmware for the DXL Board, it is based on the Rhoban fork of the LibMaple
First, you will need the ARM cortex toolchain:
sudo apt-get install libstdc++-arm-none-eabi-newlib gcc-arm-none-eabi libnewlib-arm-none-eabi binutils-arm-none-eabi dfu-util
Then, run the following commands:
./prepare.sh
make
make install
make install will send the program to the board using the DFU maple bootloader.
The board will appear as a virtual serial port (typically /dev/ttyACM0 on linux).
You can directly send dynamixel packet through it.
Note that we confgure our servos as following:
- Baudrate: 1000000
- Return delay to minimum
- Status return level to 1 (only answer READ and not on WRITE)
To take advantage of the 3 buses, there is a pseudo Sync Read command implemented in the controller.
Note that you'll have to configure your servos to have the smallest possible return delay time.
The mapping of what device is on which bus is done on-the-fly when a response is received. Thus, you may want to ping each device at the begining to be sure the mapping is OK (it's a good practice anyway to check that all the devices are present).
If you want to read N bytes at address A from M motors, here is the instruction
packet:
| ID | Instruction | Length | Data |
|---|---|---|---|
| Broadcast | 0x84 |
M+2 | A, N, ID1, ID2 ... IDM |
Then, the board will send regular read packets on the buses, in parallel. Currently,
the timeout for these reads is hard coded 650 µS.
The response will then be:
| ID | Instruction | Length | Data |
|---|---|---|---|
| Broadcast | 0x84 |
(1 + N) * M |
STATUS1, DATA1 (N bytes), STATUS2, DATA2 ... STATUSM, DATAM |
The STATUSX byte is the error field from the motor respond. In case of timeout, this
value will be 0xFF.
The GY-85 IMU is accessed using I²C bus and the raw values can be retrieved the same way you read from a dynamixel device.
The dynamixel model of the imu will be 350 and its ID is 241.
To read the IMU, you should ask for 110 bytes from the 0x24 address. Here is what you
will receive:
| Field | Size | Encoding |
|---|---|---|
| Accelerometer X | 16 bits signed | Values for the accelerometer (raw) |
| Accelerometer Y | 16 bits signed | |
| Accelerometer Z | 16 bits signed | |
| Gyrometer X | 16 bits signed | Values for the gyrometer (raw) |
| Gyrometer Y | 16 bits signed | |
| Gyrometer Z | 16 bits signed | |
| Magnetometer X | 16 bits signed | Values for the magnetometer (raw) |
| Magnetometer Y | 16 bits signed | |
| Magnetometer Z | 16 bits signed | |
| Sequence | 32 bits unsigned | Sequence number |
This block of data is repeated 5 times, because the values are stored in a circular buffer. Thus, the higher sequence number is the more recent is data. Note that asking many bytes from the IMU is not very costy in the timings because the data are here pure USB (through serial emulator).
The circular buffer is used to ensure that you don't miss any packet, since dynamixel is a master/slave protocol.