self test

example/README.md

@@ -35,9 +35,6 @@ The LIS3DH can apply its built-in high-pass filter to samples [regular reading,
 
 See files: `filter-normal.c`, and `filter-reference.c`.
 
-### file: simple.c
-Basic example of how to use this device
-
 # FIFO
 Instead of polling for every single [x y z] set, a FIFO with programmable capacity ("watermark") can be used, and then dumped into memory once full.
 
@@ -59,6 +56,10 @@ Note: FIFO will not trigger a watermark interrupt (`pin1.wtm`) if the FIFO size
 
 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.
 
+### file: self-test.c
+
+Run a device self-test to see if the device is within spec. Mine apparently isn't. (must be at-rest during test).
+
 ### file: single-click.c
 
 Set up single-click detection (no latching interrupt possible)

example/self-test.c

@@ -0,0 +1,103 @@
+#define _GNU_SOURCE
+#include <unistd.h> /* usleep() */
+#include <stdio.h>
+#include <stdlib.h>
+#include "lis3dh.h"
+#include "i2c.h"
+
+/* table 4 of datasheet */
+#define ST_MIN 17
+#define ST_MAX 360
+
+/* AN3308 suggests 5 */
+#define ITERATIONS 5
+
+int main() {
+    
+    lis3dh_t lis;
+    int32_t x_nost, y_nost, z_nost; /* store avg of measurements before self-test */
+    int32_t x_st, y_st, z_st; /* store avg of self-test measurements */
+    int32_t xd, yd, zd; /* differences */
+    int i;
+
+    lis.dev.init = i2c_init;
+    lis.dev.read = i2c_read;
+    lis.dev.write = i2c_write;
+    lis.dev.sleep = usleep;
+    lis.dev.deinit = i2c_deinit;
+
+    x_nost = y_nost = z_nost = 0;
+    x_st = y_st = z_st = 0;
+    xd = yd = zd = 0;
+
+    /* initialise LIS3DH struct */
+    if (lis3dh_init(&lis)) {
+        /* error handling */
+    }
+
+    /* reset device just in case */
+    if (lis3dh_reset(&lis)) {
+        /* error handling */
+    }
+
+    lis.cfg.mode = LIS3DH_MODE_NORMAL;
+    lis.cfg.range = LIS3DH_FS_2G;
+    lis.cfg.rate = LIS3DH_ODR_50_HZ;
+
+    lis3dh_configure(&lis);
+
+    /* discard first couple of samples as datasheet suggests they are wrong/noisy */
+    for(i=0; i<15; i++) lis3dh_read(&lis);
+
+    for(i=0; i<ITERATIONS; i++) {
+        lis3dh_read(&lis);
+        x_nost += lis.acc.x;
+        y_nost += lis.acc.y;
+        z_nost += lis.acc.z;
+    }
+
+    x_nost /= ITERATIONS;
+    y_nost /= ITERATIONS;
+    z_nost /= ITERATIONS;
+
+    lis.cfg.self_test = LIS3DH_SELF_TEST_0;
+
+    lis3dh_configure(&lis);
+
+    /* discard first couple of samples as datasheet suggests they are wrong/noisy */
+    for(i=0; i<15; i++) lis3dh_read(&lis);
+
+
+    for(i=0; i<ITERATIONS; i++) {
+        lis3dh_read(&lis);
+        x_st += lis.acc.x;
+        y_st += lis.acc.y;
+        z_st += lis.acc.z;
+    }
+
+    x_st /= ITERATIONS;
+    y_st /= ITERATIONS;
+    z_st /= ITERATIONS;
+
+    xd = abs(x_st - x_nost);
+    yd = abs(y_st - y_nost);
+    zd = abs(z_st - z_nost);
+
+    printf("variance min=%d, max=%d\n", ST_MIN, ST_MAX);
+    printf("xd=%d yd=%d zd=%d\n", xd, yd, zd);
+
+    if ((ST_MIN <= xd && xd <= ST_MAX) && (ST_MIN <= yd && yd <= ST_MAX) && (ST_MIN <= zd && zd <= ST_MAX)) {
+        puts("Pass");
+    } else {
+        puts("Fail");
+    }
+
+    lis3dh_reset(&lis);
+
+    /* deinitalise struct */
+    if (lis3dh_deinit(&lis)) {
+        /* error handling */
+    }
+
+    return 0;
+}

lis3dh.c

@@ -57,7 +57,7 @@ int lis3dh_configure(lis3dh_t *lis3dh) {
     ctrl_reg1 = (lis3dh->cfg.rate << 4) | 0x07;
     ctrl_reg2 = 0;
     ctrl_reg3 = 0;
-    ctrl_reg4 = (lis3dh->cfg.range << 4);
+    ctrl_reg4 = (lis3dh->cfg.range << 4) | (lis3dh->cfg.spi3w & 1);
     ctrl_reg5 = 0;
     ctrl_reg6 = 0;
     fifo_ctrl_reg = 0;
@@ -74,6 +74,9 @@ int lis3dh_configure(lis3dh_t *lis3dh) {
     ctrl_reg0 = 0;
     temp_cfg_reg = 0;
 
+    /* set self-test bits */
+    ctrl_reg4 |= (lis3dh->cfg.self_test & 0x03) << 1;
+
     /* determine whether to enable ADC or TEMP sensor */
     temp_cfg_reg |= (lis3dh->cfg.en_adc & 1) << 7;
     temp_cfg_reg |= (lis3dh->cfg.en_temp & 1) << 6;

lis3dh.h

@@ -112,6 +112,10 @@
 #define LIS3DH_FILTER_CUTOFF_2 0x02
 #define LIS3DH_FILTER_CUTOFF_1 0x03 /* lowest freq */
 
+/* Positive and negative axis self-test */
+#define LIS3DH_SELF_TEST_0      0x01
+#define LIS3DH_SELF_TEST_1      0x02
+
 
 /* Note: IA{1,2} is interrupt activity {1,2} or interrupt generators */
 /* user provided functions, init and deinit can be set to NULL and won't be used */
@@ -226,6 +230,8 @@ struct lis3dh_config {
      *      - time_window
      *      - time_latency
      * used in CLICK)
+     * 
+     * this is the "1[LSb]" in act_dur calc
      */
     uint8_t int1_dur; /* 7-bit INT 1 duration value */
     uint8_t int2_dur; /* 7-bit INT 2 duration value */
@@ -242,6 +248,8 @@ struct lis3dh_config {
     uint8_t sdo_pullup; /* Use pull-up on SDO. default 0 use */
     uint8_t en_adc; /* enable ADC */
     uint8_t en_temp; /* enable temp sensor on ADC 3 */
+    uint8_t spi3w; /* set to 1 to enable 3-way SPI, default 0 */
+    uint8_t self_test; /* set self-test mode */
 
     uint8_t reference; /* HP filter reference */
 };