To get good touchscreen results filtering is essential.
The filter does 2 things - it removes "bad" measurements,
and it uses average to smooth the coordinates.
Use the HW-filter in the tsc2301 to remove high frequency
noise (from backlight). Using 8 sample average is very
efficient.
Another source of noise is the screen, but that generates
low freq noise and thus require a SW filter. Using 4
coordinate history average is efficient.
Signed-off-by: Klaus Pedersen <klaus.k.pedersen@xxxxxxxxx>
---
arch/arm/mach-omap2/board-n800.c | 4 +-
drivers/input/touchscreen/tsc2301_ts.c | 81 +++++++++++++++++++++++++------
2 files changed, 67 insertions(+), 18 deletions(-)
diff --git a/arch/arm/mach-omap2/board-n800.c b/arch/arm/mach-omap2/board-n800.c
index 542e804..f161f8d 100644
--- a/arch/arm/mach-omap2/board-n800.c
+++ b/arch/arm/mach-omap2/board-n800.c
@@ -330,7 +330,7 @@ static void __init n800_ts_set_config(void)
if (conf != NULL) {
if (strcmp(conf->panel_name, "lph8923") == 0) {
tsc2301_config.ts_x_plate_ohm = 180;
- tsc2301_config.ts_hw_avg = 4;
+ tsc2301_config.ts_hw_avg = 8;
tsc2301_config.ts_max_pressure = 2048;
tsc2301_config.ts_touch_pressure = 400;
tsc2301_config.ts_stab_time = 100;
@@ -341,7 +341,7 @@ static void __init n800_ts_set_config(void)
tsc2301_config.ts_y_fudge = 7;
} else if (strcmp(conf->panel_name, "ls041y3") == 0) {
tsc2301_config.ts_x_plate_ohm = 280;
- tsc2301_config.ts_hw_avg = 16;
+ tsc2301_config.ts_hw_avg = 8;
tsc2301_config.ts_touch_pressure = 400;
tsc2301_config.ts_max_pressure = 2048;
tsc2301_config.ts_stab_time = 1000;
diff --git a/drivers/input/touchscreen/tsc2301_ts.c b/drivers/input/touchscreen/tsc2301_ts.c
index 148d8be..393bba8 100644
--- a/drivers/input/touchscreen/tsc2301_ts.c
+++ b/drivers/input/touchscreen/tsc2301_ts.c
@@ -100,6 +100,21 @@
#define MAX_12BIT ((1 << 12) - 1)
+#define TS_RECT_SIZE 8
+#define TSF_MIN_Z1 100
+#define TSF_MAX_Z2 4000
+
+#define TSF_SAMPLES 4
+
+struct ts_filter {
+ int sample_cnt;
+
+ int avg_x;
+ int avg_y;
+ int avg_z1;
+ int avg_z2;
+};
+
struct tsc2301_ts {
struct input_dev *idev;
char phys[32];
@@ -110,11 +125,12 @@ struct tsc2301_ts {
struct spi_message read_msg;
u16 data[4];
+ struct ts_filter filter;
+
int hw_avg_max;
u16 x;
u16 y;
u16 p;
- int sample_cnt;
u16 x_plate_ohm;
int stab_time;
@@ -291,25 +307,58 @@ static void update_pen_state(struct tsc2301_ts *ts, int x, int y, int pressure)
static int filter(struct tsc2301_ts *ts, int x, int y, int z1, int z2)
{
- int pressure, pressure_limit;
-
- if (z1) {
- pressure = ts->x_plate_ohm * x;
- pressure /= 4096;
- pressure *= z2 - z1;
- pressure /= z1;
- } else
- pressure = 0;
-
- /* If pressure value is above a preset limit (pen is barely
- * touching the screen) we can't trust the coordinate values.
- */
+ int inside_rect, pressure_limit, Rt;
+ struct ts_filter *tsf = &ts->filter;
+
+ /* validate pressure and position */
+ if (x > MAX_12BIT || y > MAX_12BIT)
+ return 0;
+
+ /* skip coords if the pressure-components are out of range */
+ if (z1 < TSF_MIN_Z1 || z2 > TSF_MAX_Z2)
+ return 0;
+
+ /* Use the x,y,z1,z2 directly on the first "pen down" event */
+ if (ts->event_sent) {
+ tsf->avg_x += x;
+ tsf->avg_y += y;
+ tsf->avg_z1 += z1;
+ tsf->avg_z2 += z2;
+
+ if (++tsf->sample_cnt < TSF_SAMPLES)
+ return 0;
+ x = tsf->avg_x / TSF_SAMPLES;
+ y = tsf->avg_y / TSF_SAMPLES;
+ z1 = tsf->avg_z1 / TSF_SAMPLES;
+ z2 = tsf->avg_z2 / TSF_SAMPLES;
+ }
+ tsf->sample_cnt = 0;
+ tsf->avg_x = 0;
+ tsf->avg_y = 0;
+ tsf->avg_z1 = 0;
+ tsf->avg_z2 = 0;
+
pressure_limit = ts->event_sent? ts->max_pressure: ts->touch_pressure;
- if (pressure < pressure_limit && x < MAX_12BIT && y < MAX_12BIT) {
+ /* z1 is always at least 100: */
+ Rt = x * (z2 - z1) / z1;
+ Rt = Rt * ts->x_plate_ohm / 4096;
+ if (Rt > pressure_limit)
+ return 0;
+
+ /* discard the event if it still is within the previous rect - unless
+ * if the pressure is harder, but then use previous x,y position */
+ inside_rect = (
+ x > (int)ts->x - TS_RECT_SIZE && x < (int)ts->x + TS_RECT_SIZE &&
+ y > (int)ts->y - TS_RECT_SIZE && y < (int)ts->y + TS_RECT_SIZE);
+
+ if (!ts->event_sent || !inside_rect) {
ts->x = x;
ts->y = y;
- ts->p = pressure;
+ ts->p = Rt;
+ return 1;
+ } else if (Rt < ts->p) {
+ ts->p = Rt;
return 1;
}
return 0;
--
1.5.3.3
-
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