[PATCH synaptics v2 08/21] Introduce POLL_MS for packet frequency
Daniel Stone
daniel at fooishbar.org
Tue Jun 14 10:05:56 PDT 2011
We expect to be receiving a steady 80 packets/sec (which gives 40
reports/sec with more than one finger on the pad, as Advanced Gesture
Mode requires two PS/2 packets per report). Instead of a random
scattering of magic 13 and 20ms numbers scattered throughout the driver,
introduce POLL_MS as 14ms.
Having this here allows us to call back at a steady frequency to ensure
that the finger motion remains steady.
Signed-off-by: Daniel Stone <daniel at fooishbar.org>
---
src/synaptics.c | 26 +++++++++++++++++++++-----
1 files changed, 21 insertions(+), 5 deletions(-)
v2: Fairly extensive commentary added.
diff --git a/src/synaptics.c b/src/synaptics.c
index e863081..95faa42 100644
--- a/src/synaptics.c
+++ b/src/synaptics.c
@@ -92,6 +92,21 @@ typedef enum {
LEFT_TOP_EDGE = TOP_EDGE | LEFT_EDGE
} edge_type;
+/*
+ * We expect to be receiving a steady 80 packets/sec (which gives 40
+ * reports/sec with more than one finger on the pad, as Advanced Gesture Mode
+ * requires two PS/2 packets per report). Instead of a random scattering of
+ * magic 13 and 20ms numbers scattered throughout the driver, introduce
+ * POLL_MS as 14ms, which is slightly less than 80Hz. 13ms is closer to
+ * 80Hz, but if the kernel event reporting was even slightly delayed,
+ * we would produce synthetic motion followed immediately by genuine
+ * motion, so use 14.
+ *
+ * We use this to call back at a constant rate to at least produce the
+ * illusion of smooth motion. It works a lot better than you'd expect.
+*/
+#define POLL_MS 14
+
#define MAX(a, b) (((a)>(b))?(a):(b))
#define MIN(a, b) (((a)<(b))?(a):(b))
#define TIME_DIFF(a, b) ((int)((a)-(b)))
@@ -1858,9 +1873,10 @@ ComputeDeltas(SynapticsPrivate *priv, const struct SynapticsHwState *hw,
goto out;
}
- /* to create fluid edge motion, call back 'soon'
- * even in the absence of new hardware events */
- delay = MIN(delay, 13);
+ /* To create the illusion of fluid motion, call back at roughly the report
+ * rate, even in the absence of new hardware events; see comment above
+ * POLL_MS declaration. */
+ delay = MIN(delay, POLL_MS);
if (priv->count_packet_finger <= 3) /* min. 3 packets, see get_delta() */
goto skip; /* skip the lot */
@@ -2202,7 +2218,7 @@ HandleScrolling(SynapticsPrivate *priv, struct SynapticsHwState *hw,
double dtime = (hw->millis - HIST(0).millis) / 1000.0;
double ddy = para->coasting_friction * dtime;
priv->autoscroll_y += priv->autoscroll_yspd * dtime;
- delay = MIN(delay, 20);
+ delay = MIN(delay, POLL_MS);
while (priv->autoscroll_y > 1.0) {
sd->down++;
priv->autoscroll_y -= 1.0;
@@ -2223,7 +2239,7 @@ HandleScrolling(SynapticsPrivate *priv, struct SynapticsHwState *hw,
double dtime = (hw->millis - HIST(0).millis) / 1000.0;
double ddx = para->coasting_friction * dtime;
priv->autoscroll_x += priv->autoscroll_xspd * dtime;
- delay = MIN(delay, 20);
+ delay = MIN(delay, POLL_MS);
while (priv->autoscroll_x > 1.0) {
sd->right++;
priv->autoscroll_x -= 1.0;
--
1.7.5.3
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