AP_Compass: IST8310: improve initialization

- Make sure device is reset while initializing.
 - Give better names to register macros
 - Average X, Y and Z by 16: sensor is internally running at 200 sps
   (theoretical, ~160 pratical). The wait time is ~6msec averaging
   by 16. We do 10msec.

libraries/AP_Compass/AP_Compass_IST8310.cpp

@@ -29,18 +29,27 @@
 #define DEVICE_ID 0x10
 
 #define CNTL1_REG 0xA
-#define SINGLE_MEASUREMENT_MODE 0x1
-#define ODR_100HZ 0x6
+#define CNTL1_BIT_SINGLE_MEASUREMENT_MODE 0x1
 
 #define STAT1_REG 0x2
 #define DATA_RDY 0x1
+#define CNTL2_REG 0xB
+#define CNTL2_BIT_SRST 1
 
 #define AVGCNTL_REG 0x41
-#define AVERAGING_Y_BY_2 0x20
-#define AVERAGING_XZ_BY_4 0x04
+#define AVGCNTL_BIT_XZ_0  (0)
+#define AVGCNTL_BIT_XZ_2  (1)
+#define AVGCNTL_BIT_XZ_4  (2)
+#define AVGCNTL_BIT_XZ_8  (3)
+#define AVGCNTL_BIT_XZ_16 (4)
+#define AVGCNTL_BIT_Y_0  (0 << 3)
+#define AVGCNTL_BIT_Y_2  (1 << 3)
+#define AVGCNTL_BIT_Y_4  (2 << 3)
+#define AVGCNTL_BIT_Y_8  (3 << 3)
+#define AVGCNTL_BIT_Y_16 (4 << 3)
 
 #define PDCNTL_REG 0x42
-#define NORMAL_PULSE_DURATION 0xC0
+#define PDCNTL_BIT_PULSE_DURATION_NORMAL 0xC0
 
 #define SAMPLING_PERIOD_USEC (10 * USEC_PER_MSEC)
 
@@ -74,6 +83,8 @@ AP_Compass_IST8310::AP_Compass_IST8310(Compass &compass,
 
 bool AP_Compass_IST8310::init()
 {
+    uint8_t reset_count = 0;
+
     if (!_dev->get_semaphore()->take(HAL_SEMAPHORE_BLOCK_FOREVER)) {
         return false;
     }
@@ -88,8 +99,28 @@ bool AP_Compass_IST8310::init()
         goto fail;
     }
 
-    if (!_dev->write_register(AVGCNTL_REG, AVERAGING_Y_BY_2 | AVERAGING_XZ_BY_4) ||
-        !_dev->write_register(PDCNTL_REG, NORMAL_PULSE_DURATION)) {
+    for (; reset_count < 5; reset_count++) {
+        if (!_dev->write_register(CNTL2_REG, CNTL2_BIT_SRST)) {
+            hal.scheduler->delay(10);
+            continue;
+        }
+
+        hal.scheduler->delay(10);
+
+        uint8_t cntl2 = 0xFF;
+        if (_dev->read_registers(CNTL2_REG, &cntl2, 1) &&
+            (cntl2 & 0x01) == 0) {
+            break;
+        }
+    }
+
+    if (reset_count == 5) {
+        fprintf(stderr, "IST8310: failed to reset device\n");
+        goto fail;
+    }
+
+    if (!_dev->write_register(AVGCNTL_REG, AVGCNTL_BIT_Y_16 | AVGCNTL_BIT_XZ_16) ||
+        !_dev->write_register(PDCNTL_REG, PDCNTL_BIT_PULSE_DURATION_NORMAL)) {
         fprintf(stderr, "IST8310: found device but could not set it up\n");
         goto fail;
     }
@@ -128,7 +159,7 @@ fail:
 
 void AP_Compass_IST8310::start_conversion()
 {
-    if (!_dev->write_register(CNTL1_REG, SINGLE_MEASUREMENT_MODE)) {
+    if (!_dev->write_register(CNTL1_REG, CNTL1_BIT_SINGLE_MEASUREMENT_MODE)) {
         hal.util->perf_count(_perf_xfer_err);
         _need_start = true;
         return;