fth -> size; make user config more consistent

example/README.md

@@ -4,9 +4,9 @@
 Basic example of how to use this device
 
 ### file: fifo.c
-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. All FIFO readings use 10-bit resolution regardless of the mode set in `lis.cfg.mode`. The watermark level can be adjusted to a value [0-31] by modifying the `lis.cfg.fifo.fth` property before calling `lis3dh_configure()`.
+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. All FIFO readings use 10-bit resolution regardless of the mode set in `lis.cfg.mode`. The watermark level can be adjusted to a value [1-32] (0 disables FIFO) by modifying the `lis.cfg.fifo.size` property before calling `lis3dh_configure()`.
 
-The LIS3DH can optionally apply a HP filter on the sample data. It can be used to greatly reduce the "DC acceleration" present.
+The LIS3DH can optionally apply a HP filter on the sampling to reduce 'static acceleration' from the data.
 
 ### file: interrupts.c
 This device supports two different interrupt "output pins," `INT1` and `INT2`. The appropriate flag must be set in either `cfg.pin1` or `cfg.pin2` and the interrupt source must be configured to trigger into `INT1` or `INT2`.

example/interrupts.c

@@ -42,7 +42,7 @@ int main() {
     lis.cfg.rate = LIS3DH_ODR_100_HZ;
     lis.cfg.fifo.mode = LIS3DH_FIFO_MODE_STREAM;
     lis.cfg.fifo.trig = LIS3DH_FIFO_TRIG_INT1; /* trigger interrupt into int pin1 */
-    /*lis.cfg.fifo.fth = 15;*/
+    /*lis.cfg.fifo.size = 15;*/
     lis.cfg.pin1.wtm = 1; /* trigger upon FIFO watermark level reached */
 
     /* set up HP filter to remove DC component */

lis3dh.c

@@ -28,7 +28,7 @@ int lis3dh_init(lis3dh_t *lis3dh) {
     memset(&lis3dh->src, 0, sizeof lis3dh->src);
 
     lis3dh->cfg.fifo.mode = 0xFF; /* in use if neq 0xFF */
-    lis3dh->cfg.fifo.fth = 31; /* default watermark level (0-indexed). */
+    lis3dh->cfg.fifo.size = 32; /* default fifo size */
 
     lis3dh->cfg.filter.mode = 0xFF; /* in use if neq 0xFF */
     lis3dh->cfg.filter.fds = 1; /* bypass OFF by default */
@@ -139,10 +139,10 @@ int lis3dh_configure(lis3dh_t *lis3dh) {
     int1_ths = lis3dh->cfg.int1_ths & 0x7F; 
     int2_ths = lis3dh->cfg.int2_ths & 0x7F;
 
-    /* set enable FIFO */
+    /* set enable FIFO if a mode is set and size (watermark) is not 0 */
-    if (lis3dh->cfg.fifo.mode != 0xFF) {
+    if (lis3dh->cfg.fifo.mode != 0xFF && lis3dh->cfg.fifo.size != 0) {
         ctrl_reg5 |= 0x40; /* bit FIFO_EN */
-        fifo_ctrl_reg |= (lis3dh->cfg.fifo.fth & 0x1F);
+        fifo_ctrl_reg |= ((lis3dh->cfg.fifo.size - 1) & 0x1F);
         fifo_ctrl_reg |= (lis3dh->cfg.fifo.mode << 6);
         fifo_ctrl_reg |= ((lis3dh->cfg.fifo.trig & 1) << 5);
     }
@@ -284,7 +284,7 @@ int lis3dh_read_fifo(lis3dh_t *lis3dh, struct lis3dh_fifo_data *fifo) {
     /* FIFO is always 10-bit / normal mode */
     sens = acc_sensitivity(LIS3DH_MODE_NORMAL, lis3dh->cfg.range);
 
-    fifo->size = lis3dh->cfg.fifo.fth;
+    fifo->size = lis3dh->cfg.fifo.size;
 
     err |= lis3dh->dev.read(REG_OUT_X_L, data, fifo->size * 6);
 

lis3dh.h

@@ -160,7 +160,7 @@ struct lis3dh_filter_config {
 
 /* config for FIFO */
 struct lis3dh_fifo_config {
-    uint8_t fth; /* user-specified watermark level 0-32 */
+    uint8_t size; /* size of fifo; 0-32; 0=don't use. fth=[1-32]-1 (index) */
     uint8_t trig; /* pin to trigger when watermark/overrun occurs */
     uint8_t mode; /* FIFO mode */
 };