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touchio.TouchIn sensing working on a single pin! adafruit/circuitpython#1048

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This commit is contained in:
Nick Moore 2018-12-11 14:33:03 +11:00
parent 901db4797e
commit 1dc4c4757e
1 changed files with 34 additions and 21 deletions
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55
ports/nrf/common-hal/touchio/TouchIn.c
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@ -45,13 +45,40 @@ bool touch_enabled = false;
#define CHANNEL_NO 0
#define N_SAMPLES 10
#define K_FACTOR 100000000L
static uint16_t process_samples(nrf_saadc_value_t samples[], int n_samples) {
// XXX sort of like a least squares fit here, with the assumption
// that the timing ('x') is stable (thus we suspend interrupts while
// taking these measurements)
int32_t sumy = 0;
int32_t sumxy = 0;
for (int i = 0; i < N_SAMPLES; i++) {
sumy += samples[i];
sumxy += i*samples[i];
}
// we don't really care about the units, and so we can cut out a
// whole bunch of stuff which is based only on N_SAMPLES, eg:
// n, sum(x), sum(x^2) and sum(x)^2 terms. This leaves only:
int16_t m = (N_SAMPLES - 1) * sumy / 2 - sumxy;
// m is proportional to the charge rate of the capacitor which is
// in reciprocal proportion to the actual capacitance.
return (uint16_t)(K_FACTOR / m);
}
static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
nrf_saadc_value_t samples[N_SAMPLES];
// Configure analog input.
// XXX cloned from AnalogIn and probably overkill
// XXX analogio.AnalogIn and this class both use SAADC channel 0
// all the time and never any other channel. This seems a bit
// silly.
const nrf_saadc_channel_config_t config = {
.resistor_p = NRF_SAADC_RESISTOR_DISABLED,
@ -75,14 +102,15 @@ static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
nrf_saadc_channel_init(CHANNEL_NO, &config);
nrf_saadc_buffer_init(samples, N_SAMPLES);
// set pad to digital output high for 20us to charge it
// set pad to digital output high for 10us to charge it
nrf_gpio_cfg_output(self->pin->number);
nrf_gpio_pin_set(self->pin->number);
mp_hal_delay_us(20);
mp_hal_delay_us(10);
// set pad back to an input and take some samples
// IRQs are suspended to make sure our samples are at fixed times.
__disable_irq();
@ -92,7 +120,7 @@ static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
while (nrf_saadc_event_check(NRF_SAADC_EVENT_STARTED) == 0);
nrf_saadc_event_clear(NRF_SAADC_EVENT_STARTED);
// XXX surely there's a better way
// XXX surely there's a better way? PPI?
for (uint32_t i = 0; i < N_SAMPLES; i++) {
nrf_saadc_task_trigger(NRF_SAADC_TASK_SAMPLE);
while (nrf_saadc_event_check(NRF_SAADC_EVENT_DONE) == 0);
@ -105,7 +133,7 @@ static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
while (nrf_saadc_event_check(NRF_SAADC_EVENT_STOPPED) == 0);
nrf_saadc_event_clear(NRF_SAADC_EVENT_STOPPED);
// turn off SAADC & set output pin low
// turn off SAADC & set output pin low (to minimize leakage currents)
nrf_gpio_pin_clear(self->pin->number);
@ -114,23 +142,8 @@ static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
nrf_gpio_cfg_output(self->pin->number);
int32_t sumy = 0;
int32_t sumxy = 0;
return process_samples(samples, N_SAMPLES);
//mp_printf(MP_PYTHON_PRINTER, "touch");
// XXX sort of like a least squares fit here
for (int i = 0; i < N_SAMPLES; i++) {
//mp_printf(MP_PYTHON_PRINTER, " %d", samples[i]);
sumy += samples[i];
sumxy += i*samples[i];
}
int32_t r = (N_SAMPLES - 1) * sumy / 2 - sumxy;
//mp_printf(MP_PYTHON_PRINTER, " -> %d %d -> %d\n", sumy, sumxy, r);
return (uint16_t)r;
}
void common_hal_touchio_touchin_construct(touchio_touchin_obj_t* self,