Libraries
Background
ADXL345.c – accelerometer device I/O for Tollos
These functions provide basic IO for using the ADXL345 accelerometer device, attached via I2C.
The following connections are assumed:
- SCL & SDA ... to I2C bus SCL & SDA, with appropriate pullups (channel is selectable)
- SDO ... to GND (selects device alternate physical bus address)
- CS ... to VCC (+3.3V) [enable I2C mode]
- INT1 ... to a suitable input bit pin
- VCC & GND ... to suitable power rails, with bypass capacitors
(INT2 is currently unused.)
This code assumes only one ADXL345 device will be used on a controller, so some state information can be held (the device channel and address). This simplifies the tollosAcc interface and allows initialization checking.
| Functions | |
|---|---|
| accGetXYZIO | read latest x, y, and z accelerations |
| accInitIO | configure and initialize accelerometer |
| accRangeIO | change range of accelerometer |
| accRateIO | change update rate of accelerometer |
| accStopIO | stop and power-down accelerometer |
accGetXYZIO – read latest x, y, and z accelerations
int accGetXYZIO(int *x, int *y, int *z);
x, y, z – receive accelerations [in milli-gs]
returns 0 if data read, −1 if the device is not initialized, or −2 if there was an error reading the data (or no data ready); 1 is returned if data overrun was raised – in this case data is read
Results are returned scaled to milli-gs (1000 = 1g), without any calibration adjustments.
This should normally be called only after a Data Ready interrupt; the interrupt is cleared by calling this.
accInitIO – configure and initialize accelerometer
int accInitIO(uint channel);
channel – I2C channel on which device is to be found
returns 0 if initialized OK, negative if error
The tollosAcc interface expects:
- an update rate of at least 25 Hz (but need not be higher than that on initialization, to save power)
- a range of at least 2g
- an interrupt [from pin INT1] when Data Ready is raised.
The caller should set up the interrupt handler before calling this function, or clear Data Ready by calling accGetXYZIO.
accRangeIO – change range of accelerometer
int accRangeIO(uint range);
range – range requested in milli-g [1000 = 1 g]
returns the chosen range if changed OK, −1 if error (range too high)
The accelerometer will be set to a smallest available range that is >= the requested range, to maximize the precision of returned results.
accRateIO – change update rate of accelerometer
int accRateIO(uint rate);
rate – rate requested [Hz, 1..200]
returns the chosen rate (nearest Hz below) if changed OK, −1 if error (rate zero or too high)
The accelerometer will be set to a slowest available rate that is >= the requested rate, to minimize resource usage.
To ensure working with 100kHz I2C, the maximum rate is limited to 200Hz – but note that this may use significant processor bandwidth.
accStopIO – stop and power-down accelerometer
int accStopIO(void);
returns 0 if accelerometer stopped OK, negative if an error or it was not running.