free-fall

example/README.md

@@ -70,3 +70,7 @@ There are two interrupt registers, `int1` and `int2` that can be configured for
 ### file: inertial-wakeup.c
 
 Inertial interrupt example in OR mode (easily changed to AND mode) with configurable axes, threshold and minimum acceleration duration.
+
+### file: free-fall.c
+
+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.

example/free-fall.c

@@ -0,0 +1,129 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <math.h>
+#include "lis3dh.h"
+#include "interrupt.h"
+#include "i2c.h"
+
+#define GPIO_INTERRUPT_PIN_INT1 12
+
+int main() {
+
+    lis3dh_t lis;
+
+    /* set fn ptrs to rw on bus (i2c or SPI) */
+    lis.dev.init = i2c_init;
+    lis.dev.read = i2c_read;
+    lis.dev.write = i2c_write;
+    lis.dev.sleep = usleep;
+    lis.dev.deinit = i2c_deinit;
+
+    /* initialise LIS3DH struct */
+    if (lis3dh_init(&lis)) {
+        /* error handling */
+    }
+
+    /* reset device just in case */
+    if (lis3dh_reset(&lis)) {
+        /* error handling */
+    }
+
+    /* register interrupt */
+    if (int_register(GPIO_INTERRUPT_PIN_INT1)) {
+        /* error handling */
+    }
+
+    /* set up config */
+    lis.cfg.mode = LIS3DH_MODE_HR;
+    lis.cfg.range = LIS3DH_FS_2G;
+    lis.cfg.rate = LIS3DH_ODR_400_HZ;
+
+    /* no filter because we want the 'absolute' experienced acceleration */
+
+    lis.cfg.pin1.ia1 = 1; /* enable INT1 through pin1 */
+    lis.cfg.int1.latch = 1; /* latch interrupt until INT1_SRC is read */
+
+    /* enable all the low directions */
+    /* this works because the low directions are compared to -threshold,
+       and are below it at rest, and greater than it at free-fall,
+       while the opposite is true for the high directions. */
+    lis.cfg.int1.xl = 1;
+    lis.cfg.int1.yl = 1;
+    lis.cfg.int1.zl = 1;
+
+    /* AND interrupt mode */
+    lis.cfg.int1.aoi = 1;
+    lis.cfg.int1.en_6d = 0;
+
+    /* 1 LSb = 16 mg @ FS_2G 
+     * Due to inherent problems with accuracy and timing, you should use a "free-fall window",
+     * rather than setting the threshold to 0. AN3308 pg 27 recommends at or below 350mg for all axes,
+     * to be considered as being in a state of free-fall, but the gradual return to experiencing
+     * 1g in free-fall is not discussed.
+     * 
+     * 350/16 ~= 20
+     */
+    lis.cfg.int1_ths = 20;
+
+    /*
+     * Duration time is measured in N/ODR where:
+     * --- N = The content of the intX_dur integer
+     * --- ODR = the data rate, eg 100, 400...
+     * [ODR] [1 LSb in milliseconds]
+     *   400    2.5
+     * 
+     * At 400 ODR,
+     * 30 ms = 30/2.5 = 12
+     */
+    lis.cfg.int1_dur = 12;
+    
+    /* write device config */
+    if (lis3dh_configure(&lis)) {
+        /* error handling */
+    }
+
+    /* read INT1_SRC to clear previous interrupts, if any */
+    if (lis3dh_read_int1(&lis)) {
+        /* error handling */
+    }
+
+    for ( ;; ) {
+
+         /* poll interrupt on INT1 pin */
+        if (int_poll(GPIO_INTERRUPT_PIN_INT1)) {
+            /* error handling */
+        }
+
+        /* read INT1_SRC when interrupt has fired */
+        if (lis3dh_read_int1(&lis)) {
+            /* error handling */
+        }
+
+        /* only print if IA=1 */
+        if (LIS3DH_INT_SRC_IA(lis.src.int1)) {
+            /* print received interrupt .. */
+            printf("IA=%d ZH=%d ZL=%d YH=%d YL=%d XH=%d XL=%d\n",
+                LIS3DH_INT_SRC_IA(lis.src.int1),
+                LIS3DH_INT_SRC_Z_HIGH(lis.src.int1),
+                LIS3DH_INT_SRC_Z_LOW(lis.src.int1),
+                LIS3DH_INT_SRC_Y_HIGH(lis.src.int1),
+                LIS3DH_INT_SRC_Y_LOW(lis.src.int1),
+                LIS3DH_INT_SRC_X_HIGH(lis.src.int1),
+                LIS3DH_INT_SRC_X_LOW(lis.src.int1));
+        }
+    }
+    
+    /* unregister interrupt */
+    if (int_unregister(GPIO_INTERRUPT_PIN_INT1)) {
+        /* error handling */
+    }
+
+    /* deinitalise struct */
+    if (lis3dh_deinit(&lis)) {
+        /* error handling */
+    }
+
+    return 0;
+}

example/single-click.c

@@ -107,6 +107,10 @@ int main() {
                 LIS3DH_CLICK_SCLICK(lis.src.click),
                 LIS3DH_CLICK_DCLICK(lis.src.click));
         }
+
+        /* sleep for 5 ms because gpio sysfs is slow at clearing interrupts */
+        /* not necessary with "real" IRQ */
+        usleep(5000);
     }
     
     /* unregister interrupt */