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Input: ads7846 - optionally leave Vref on during differential measurements

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On some LCDs leaving the Vref on provides much better readings.

Signed-off-by: Jarkko Oikarinen <jarkko.oikarinen@nokia.com>
Signed-off-by: Imre Deak <imre.deak@solidboot.com>
Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
This commit is contained in:
Imre Deak 2007-01-18 00:45:21 -05:00 committed by Dmitry Torokhov
parent da970e69ef
commit de2defd96d
2 changed files with 19 additions and 13 deletions
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30
drivers/input/touchscreen/ads7846.c
View file

@ -145,15 +145,16 @@ struct ads7846 {
#define MAX_12BIT ((1<<12)-1)
/* leave ADC powered up (disables penirq) between differential samples */
#define READ_12BIT_DFR(x) (ADS_START | ADS_A2A1A0_d_ ## x \
| ADS_12_BIT | ADS_DFR)
#define READ_12BIT_DFR(x, adc, vref) (ADS_START | ADS_A2A1A0_d_ ## x \
| ADS_12_BIT | ADS_DFR | \
(adc ? ADS_PD10_ADC_ON : 0) | (vref ? ADS_PD10_REF_ON : 0))
#define READ_Y (READ_12BIT_DFR(y) | ADS_PD10_ADC_ON)
#define READ_Z1 (READ_12BIT_DFR(z1) | ADS_PD10_ADC_ON)
#define READ_Z2 (READ_12BIT_DFR(z2) | ADS_PD10_ADC_ON)
#define READ_Y(vref) (READ_12BIT_DFR(y, 1, vref))
#define READ_Z1(vref) (READ_12BIT_DFR(z1, 1, vref))
#define READ_Z2(vref) (READ_12BIT_DFR(z2, 1, vref))
#define READ_X (READ_12BIT_DFR(x) | ADS_PD10_ADC_ON)
#define PWRDOWN (READ_12BIT_DFR(y) | ADS_PD10_PDOWN) /* LAST */
#define READ_X(vref) (READ_12BIT_DFR(x, 1, vref))
#define PWRDOWN (READ_12BIT_DFR(y, 0, 0)) /* LAST */
/* single-ended samples need to first power up reference voltage;
* we leave both ADC and VREF powered
@ -161,8 +162,8 @@ struct ads7846 {
#define READ_12BIT_SER(x) (ADS_START | ADS_A2A1A0_ ## x \
| ADS_12_BIT | ADS_SER)
#define REF_ON (READ_12BIT_DFR(x) | ADS_PD10_ALL_ON)
#define REF_OFF (READ_12BIT_DFR(y) | ADS_PD10_PDOWN)
#define REF_ON (READ_12BIT_DFR(x, 1, 1))
#define REF_OFF (READ_12BIT_DFR(y, 0, 0))
/*--------------------------------------------------------------------------*/
@ -670,6 +671,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
struct ads7846_platform_data *pdata = spi->dev.platform_data;
struct spi_message *m;
struct spi_transfer *x;
int vref;
int err;
if (!spi->irq) {
@ -767,6 +769,8 @@ static int __devinit ads7846_probe(struct spi_device *spi)
input_set_abs_params(input_dev, ABS_PRESSURE,
pdata->pressure_min, pdata->pressure_max, 0, 0);
vref = pdata->keep_vref_on;
/* set up the transfers to read touchscreen state; this assumes we
* use formula #2 for pressure, not #3.
*/
@ -776,7 +780,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
spi_message_init(m);
/* y- still on; turn on only y+ (and ADC) */
ts->read_y = READ_Y;
ts->read_y = READ_Y(vref);
x->tx_buf = &ts->read_y;
x->len = 1;
spi_message_add_tail(x, m);
@ -794,7 +798,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
/* turn y- off, x+ on, then leave in lowpower */
x++;
ts->read_x = READ_X;
ts->read_x = READ_X(vref);
x->tx_buf = &ts->read_x;
x->len = 1;
spi_message_add_tail(x, m);
@ -813,7 +817,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
spi_message_init(m);
x++;
ts->read_z1 = READ_Z1;
ts->read_z1 = READ_Z1(vref);
x->tx_buf = &ts->read_z1;
x->len = 1;
spi_message_add_tail(x, m);
@ -830,7 +834,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
spi_message_init(m);
x++;
ts->read_z2 = READ_Z2;
ts->read_z2 = READ_Z2(vref);
x->tx_buf = &ts->read_z2;
x->len = 1;
spi_message_add_tail(x, m);

2
include/linux/spi/ads7846.h
View file

@ -14,6 +14,8 @@ enum ads7846_filter {
struct ads7846_platform_data {
u16 model; /* 7843, 7845, 7846. */
u16 vref_delay_usecs; /* 0 for external vref; etc */
int keep_vref_on:1; /* set to keep vref on for differential
* measurements as well */
u16 x_plate_ohms;
u16 y_plate_ohms;