The LIS3DH can apply its built-in high-pass filter to samples [regular reading, FIFO reading] and some specific user-functions. It has 3 different modes.
| mode | symbol | description |
|------|--------|-------------|
| Normal | `LIS3DH_FILTER_MODE_NORMAL` | Use `lis3dh_reference()` to set the filter to the current accel field, without having to wait for it to settle at/near it. |
| Autoreset | `LIS3DH_FILTER_MODE_AUTORESET` | Same as `normal` but this mode also automatically resets itself upon an interrupt(*). |
| REFERENCE | `LIS3DH_FILTER_MODE_REFERENCE` | Output data is calculated as the difference between `cfg.reference` and the measured acceleration. |
\* INT by the generator which the filter is programmed to apply itself to.
See files: `filter-normal.c`, and `filter-reference.c`.
| FIFO | `LIS3DH_FIFO_MODE_FIFO` | FIFO can be read/emptied at any time but once overrun has to be reset. See files: `fifo-int-ovrn.c`, `fifo-int-wtm.c`, `fifo.c` |
| Stream | `LIS3DH_FIFO_MODE_STREAM` | FIFO continously writes new data at 1/ODR and will overwrite old data until it is read/emptied. See files: `stream-int-ovrn.c`, `stream-int-wtm.c`, `stream.c` |
Note: FIFO will not trigger a watermark interrupt (`pin1.wtm`) if the FIFO size is default (32; maximum size). To use the watermark interrupt, the FIFO size has to be between [1-31]. An overrun interrupt (`pin1.overrun`) will always trigger when the FIFO is full, regardless of programmed capacity.
Note: to sample data faster than 200 Hz, it is necessary to use the regular data polling functionality using `lis3dh_read()` with the appropriate configuration. See files `simple.c` and `fast.c` for examples.
There are two interrupt registers, `int1` and `int2` that can be configured for inertial interrupts. The config structs are identical and contain the fields: `zh`, `zl`, `yh`, `yl`, `xh`, `xl`, and more. `zh` stands for `Z_axis_high` and `zl` stands for `Z_axis_low`. If both are enabled, the device will generate an interrupt upon Z-axis acceleration exceeding `threshold`, or upon Z-axis acceleration reading at or below `-threshold` (in OR mode. Not possible in AND mode).
An interrupt is generated when at least one of the configured axes is at or above the threshold level.
#### 6D MOVEMENT recognition
An interrupt is generated when the device moves from a direction (known or unknown) to a different known direction. The interrupt is only active for 1/ODR.
#### AND combination
An interrupt is generated when all of the configures axes are at or above the threshold level.
Inertial interrupt example activating upon free-fall. It works by using an AND mode interrupt of all the negative axes and comparing them to a threshold value (in the case of negative axis the threshold is multiplied by -1), recommended to be at 350mg (for >30 ms) and activating when the experienced negative acceleration is greater (abs. sense) than the negative threshold.
### file: 6d-movement.c
Inertial interrupt example, generates an interrupt when some acceleration, `threshold` is experienced on any configured axis for `duration` time. Supposedly the device knows what a "known" direction is.
### file: 6d-position.c
Inertial interrupt example, the interrupt line is kept active so long as the device is stable (ie acceleration on configured axes does not exceed `threshold` for `duration` time).
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### 4D detection
4D detection is a subset of 6D detection meant for detecting portrait/landscape screen rotations on mobile phones, etc. It functionally works the same as the 6D modes, except that detection along the Z-axis is disabled.
### file: 4d-movement.c
Inertial interrupt example, generates an interrupt when some acceleration, `threshold` is experienced on any configured axis for `duration` time. Supposedly the device knows what a "known" direction is.
### file: 4d-position.c
Inertial interrupt example, the interrupt line is kept active so long as the device is stable (ie acceleration on configured axes does not exceed `threshold` for `duration` time).
The LIS3DH can be programmed to automatically enter a slow, low-power mode until it detects a specific event (acceleration exceeding `threshold`). Then, it will enter the mode set in `cfg.{mode,rate}` and behave as normal, until the `duration` since the beginning of sensing event has elapsed.
The device, if configured with any non-zero values in `cfg.act_ths` and `cfg.act_dur` immediately enters low-power mode and will remain so until it experiences an acceleration [OR combination of all axes] that exceeds `threshold`. Upon experiencing such an acceleration, the device will activate `INT2` (configurable) and for a period of time (specified in `cfg.act_dur`) behave as normal, i.e. use the mode set in `cfg`.
When the time period (specified in `cfg.act_dur`) has elapsed, the device will trigger on `INT2` (configurable) again, and enter low-power mode. This cycle continues indefinitely.