More information, sleep-to-wake, and re-work FIFO examples
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# lis3dh/example
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The LIS3DH has 3 operating modes.
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| mode | symbol | description |
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|------|---------|------------|
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| LP | `LIS3DH_MODE_LP` | Low-power mode. 8-bit acc. reading resolution. |
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| Normal | `LIS3DH_MODE_NORMAL` | "Normal" mode. 10-bit acc. reading resolution. |
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| HR | `LIS3DH_MODE_HR` | High-resolution mode. 12-bit acc. reading resolution. |
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There are serveral `ODR` (internal data/sample rate) options, but some may only be used in a specific operating mode.
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| ODR | mode | symbol |
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|-----|------|--------|
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| 1 Hz | any | `LIS3DH_ODR_1_HZ` |
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| 10 Hz | any | `LIS3DH_ODR_10_HZ` |
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| 25 Hz | any | `LIS3DH_ODR_25_HZ` |
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| 50 Hz | any | `LIS3DH_ODR_50_HZ` |
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| 100 Hz | any | `LIS3DH_ODR_100_HZ` |
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| 200 Hz | any | `LIS3DH_ODR_200_HZ` |
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| 400 Hz | any | `LIS3DH_ODR_400_HZ` |
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| 1344 Hz | Normal | `LIS3DH_ODR_NORM_1344_HZ` |
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| 1600 Hz | LP | `LIS3DH_ODR_LP_1600_HZ` |
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| 5376 Hz | LP | `LIS3DH_ODR_LP_5376_HZ` |
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### file: simple.c
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Basic example of how to use this device
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@ -12,7 +33,6 @@ The watermark level can be adjusted to a value [1-32] (0 disables FIFO) by modif
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The FIFO "engine" samples/appends another set of [x y z] values at 1/ODR. The maximum ODR supported by the FIFO "engine" is 200 Hz.
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**files in `fifo/` dir**
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| FIFO mode | symbol | description |
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|------------------|-----------------------|----------------------------|
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@ -107,3 +127,12 @@ Inertial interrupt example, generates an interrupt when some acceleration, `thre
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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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# "Sleep to Wake" and "Return to Sleep"
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The LIS3DH can be programmed to automatically switch to `LP` mode upon recognition of a specific event. Once the event is over, the device will return to whatever mode it was in before the event.
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When the experienced acceleration [OR combination of all axes] falls below the `threshold` value stored in `cfg.act_ths`, the device automatically switches to `LP` mode with an ODR of 10 Hz. The duration of "normal function", the Wake period duration, is specified in `cfg.act_dur`.
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As soon as the experienced acceleration rises above the threshold, the device restores the original mode and ODR.
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See file: `sleep-to-wake.c`.
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example/sleep-to-wake.c
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119
example/sleep-to-wake.c
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#define _GNU_SOURCE
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#include <unistd.h> /* usleep() */
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#include <stdio.h>
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#include "lis3dh.h"
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#include "interrupt.h"
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#include "i2c.h"
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/* LIS3DH INT2 connected to Raspberry Pi GPIO 16 (Pin 36) */
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#define GPIO_INTERRUPT_PIN_INT2 16
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int main() {
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lis3dh_t lis;
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lis.dev.init = i2c_init;
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lis.dev.read = i2c_read;
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lis.dev.write = i2c_write;
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lis.dev.sleep = usleep;
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lis.dev.deinit = i2c_deinit;
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/* initialise LIS3DH struct */
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if (lis3dh_init(&lis)) {
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/* error handling */
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}
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/* reset device just in case */
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if (lis3dh_reset(&lis)) {
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/* error handling */
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}
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/* register interrupt on specified pin */
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if (int_register(GPIO_INTERRUPT_PIN_INT2)) {
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/* error handling */
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}
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lis.cfg.mode = LIS3DH_MODE_HR;
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lis.cfg.range = LIS3DH_FS_2G;
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lis.cfg.rate = LIS3DH_ODR_400_HZ;
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/* enable ACT function through INT PIN 2 */
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/* interrupts must be used, there is no reg to poll */
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lis.cfg.pin2.act = 1;
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/* This functionality cannot be filtered internally !! */
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/* 1 LSb = 16 mg @ FS_2G
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* 1 LSb = 32 mg @ FS_4G
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* 1 LSb = 62 mg @ FS_8G
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* 1 LSb = 186 mg @ FS_16G
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*
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* @ FS_2G
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* Wake up when acceleration goes above 1.3g .. (any axis)
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* 1.3g / 16mg = 1300/16 = N LSb = 81.25 ~ 81
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*/
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/* This controls activity recognition */
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lis.cfg.act_ths = 81; /* 7-bit ; must be > 1*/
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/* Sleep-to-wake and return-to-sleep duration
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* 1 LSb = (8 * 1[LSb] + 1) / ODR
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* Confusing formulation !
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*
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* [ODR] [1 LSb in milliseconds]
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* 1 1000
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* 10 100
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* 25 40
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* 50 20
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* 100 10
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* 200 5
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* 400 2.5
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*
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* Full table in lis3dh.h
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*
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* 1 LSb = (8 * N[2.5ms] + 1) / ODR ( @ ODR=400Hz )
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* 1 LSb = (8 * N[LSb] + 1) / ODR ( @ ODR=400Hz )
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*
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* So, 5000 ms => (8 * N[2.5] + 1) / ODR ; solve N=time(ms)/2.5
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* => (8 * 2000[LSb] + 1) / ODR
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* => (8 * 2000 + 1) / ODR
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* => 16001 / 400
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* => 40
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*
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* After `act_ths' worth of acceleration has been felt;
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* Stay in Wake mode for 5000 ms
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*/
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/* This controls return-to-sleep */
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lis.cfg.act_dur = 40; /* 8-bit ; range 0-255 */
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/* write device config */
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if (lis3dh_configure(&lis)) {
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/* error handling */
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}
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for ( ;; ) {
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/* wait until INT2 goes active (Wake mode) */
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if (int_poll(GPIO_INTERRUPT_PIN_INT2)) {
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/* error handling */
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}
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/* Do "work" here at high ODR, HR mode, etc. */
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puts("I am awake!");
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/* wait until INT2 goes inactive (Sleep mode) */
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if (int_poll(GPIO_INTERRUPT_PIN_INT2)) {
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/* error handling */
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}
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puts("Sleeping...");
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}
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/* deinitalise struct */
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if (lis3dh_deinit(&lis)) {
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/* error handling */
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}
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return 0;
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}
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