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speed up measurement loop

This commit is contained in:
Nick Moore 2019-01-27 21:54:59 +11:00
parent 4a093294ac
commit 539aaf08b5
1 changed files with 11 additions and 3 deletions
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14
ports/nrf/common-hal/touchio/TouchIn.c
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@ -38,8 +38,17 @@
#include "nrf.h"
// This is a capacitive touch sensing routine using a single digital
// pin. The pin should be connected to the sensing pad, and to ground
// via a 1Mohm or thereabout drain resistor. When a reading is taken,
// the pin's capacitance is charged by setting it to a digital output
// 'high' for a few microseconds, and then it is changed to a high
// impedance input. We measure how long it takes to discharge through
// the resistor (around 50us), using a busy-waiting loop, and average
// over N_SAMPLES cycles to reduce the effects of noise.
#define N_SAMPLES 10
#define TIMEOUT_US 10000
#define TIMEOUT_TICKS 10000
static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
@ -57,9 +66,8 @@ static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
nrf_gpio_cfg_input(self->pin->number, NRF_GPIO_PIN_NOPULL);
while(nrf_gpio_pin_read(self->pin->number)) {
if (ticks >= TIMEOUT_US) return TIMEOUT_US;
if (ticks >= TIMEOUT_TICKS) return TIMEOUT_TICKS;
ticks++;
mp_hal_delay_us(1);
}
}
return ticks;