Merge pull request #229 from rieck/lis2dw_fifo_fix

Clamp the lis2dw FIFO count and read it in one burst

legacy/watch_faces/sensor/accelerometer_data_acquisition_face.c

@@ -448,13 +448,13 @@ static void start_reading(accelerometer_data_acquisition_state_t *state) {
 
     state->records[state->pos++] = record;
     lis2dw_fifo_t fifo;
-    lis2dw_read_fifo(&fifo, LIS2DW_FIFO_TIMEOUT); // dump the fifo, this starts a fresh round of data in continue_reading
+    lis2dw_read_fifo(&fifo); // dump the fifo, this starts a fresh round of data in continue_reading
 }
 
 static void continue_reading(accelerometer_data_acquisition_state_t *state) {
     printf("Continue reading\n");
     lis2dw_fifo_t fifo;
-    lis2dw_read_fifo(&fifo, LIS2DW_FIFO_TIMEOUT);
+    lis2dw_read_fifo(&fifo);
 
     fifo.count = min(fifo.count, 25); // hacky, but we need a consistent data rate; if we got a 26th data point, chuck it.
     uint8_t offset = 4 * (25 - fifo.count); // also hacky: we're sometimes short at the start. align to beginning of next second.

watch-faces/sensor/lis2dw_monitor_face.c

@@ -417,7 +417,7 @@ static void _monitor_update(lis2dw_monitor_state_t *state)
     lis2dw_fifo_t fifo;
     float x = 0, y = 0, z = 0;
 
-    lis2dw_read_fifo(&fifo, LIS2DW_FIFO_TIMEOUT / DISPLAY_FREQUENCY);
+    lis2dw_read_fifo(&fifo);
     if (fifo.count == 0) {
         return;
     }

watch-library/shared/driver/lis2dw.c

@@ -277,26 +277,32 @@ inline void lis2dw_disable_fifo(void) {
 #endif
 }
 
-bool lis2dw_read_fifo(lis2dw_fifo_t *fifo_data, uint32_t timeout) {
+bool lis2dw_read_fifo(lis2dw_fifo_t *fifo_data) {
-    // timeout is in terms of 1/RTC_CNT_HZ seconds (likely 128 timeouts is one second)
 #ifdef I2C_SERCOM
     uint8_t temp = watch_i2c_read8(LIS2DW_ADDRESS, LIS2DW_REG_FIFO_SAMPLE);
     bool overrun = !!(temp & LIS2DW_FIFO_SAMPLE_OVERRUN);
 
     fifo_data->count = temp & LIS2DW_FIFO_SAMPLE_COUNT;
 
-    rtc_counter_t timeout_counter = watch_rtc_get_counter() + timeout;
+    /* The count field can report up to 63, but readings[] only holds 32.
-    for(int i = 0; i < fifo_data->count; i++) {
+       Clamp so a glitched or overrun count can't overflow the buffer. */
-        if (watch_rtc_get_counter() > timeout_counter) {
+    if (fifo_data->count > 32) {
-            break;
+        fifo_data->count = 32;
-        }
+    }
-        fifo_data->readings[i] = lis2dw_get_raw_reading();
+
+    /* Read the whole FIFO in one burst. With address auto-increment (IF_ADD_INC)
+       the pointer walks OUT_X_L..OUT_Z_H and rolls over into the next FIFO slot,
+       so count*6 bytes returns the samples back-to-back. On this little-endian
+       target the raw bytes map straight onto lis2dw_reading_t (x, y, z int16). */
+    if (fifo_data->count > 0) {
+        uint8_t reg = LIS2DW_REG_OUT_X_L | 0x80;
+        watch_i2c_send(LIS2DW_ADDRESS, &reg, 1);
+        watch_i2c_receive(LIS2DW_ADDRESS, (uint8_t *) fifo_data->readings, fifo_data->count * 6);
     }
 
     return overrun;
 #else
     (void) fifo_data;
-    (void) timeout;
     return false;
 #endif
 }

watch-library/shared/driver/lis2dw.h

@@ -301,8 +301,6 @@ typedef enum {
 #define LIS2DW_CTRL7_VAL_HP_REF_MODE        0b00000010
 #define LIS2DW_CTRL7_VAL_LPASS_ON6D         0b00000001
 
-#define LIS2DW_FIFO_TIMEOUT                 100  // timeout is in terms of 1/RTC_CNT_HZ seconds (likely 128 timeouts is one second)
-
 bool lis2dw_begin(void);
 
 uint8_t lis2dw_get_device_id(void);
@@ -347,7 +345,7 @@ void lis2dw_enable_fifo(void);
 
 void lis2dw_disable_fifo(void);
 
-bool lis2dw_read_fifo(lis2dw_fifo_t *fifo_data, uint32_t timeout);
+bool lis2dw_read_fifo(lis2dw_fifo_t *fifo_data);
 
 void lis2dw_clear_fifo(void);