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hugely simplified version of the touchio.TouchIn.get_raw_reading code (adafruit/circuitpython#1048)

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This commit is contained in:
Nick Moore 2019-01-27 15:01:48 +11:00
parent 1dc4c4757e
commit 4a093294ac
1 changed files with 15 additions and 99 deletions
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114
ports/nrf/common-hal/touchio/TouchIn.c
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@ -37,120 +37,36 @@
#include "supervisor/shared/translate.h"
#include "nrf.h"
#include "nrfx/hal/nrf_saadc.h"
#include "tick.h"
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);
}
#define TIMEOUT_US 10000
static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
nrf_saadc_value_t samples[N_SAMPLES];
uint16_t ticks = 0;
// Configure analog input.
// XXX analogio.AnalogIn and this class both use SAADC channel 0
// all the time and never any other channel. This seems a bit
// silly.
for (uint16_t i = 0; i < N_SAMPLES; i++) {
// set pad to digital output high for 10us to charge it
const nrf_saadc_channel_config_t config = {
.resistor_p = NRF_SAADC_RESISTOR_DISABLED,
.resistor_n = NRF_SAADC_RESISTOR_DISABLED,
.gain = NRF_SAADC_GAIN1_6,
.reference = NRF_SAADC_REFERENCE_INTERNAL,
.acq_time = NRF_SAADC_ACQTIME_3US,
.mode = NRF_SAADC_MODE_SINGLE_ENDED,
.burst = NRF_SAADC_BURST_DISABLED,
.pin_p = NRF_SAADC_INPUT_VDD,
.pin_n = NRF_SAADC_INPUT_VDD,
};
nrf_gpio_cfg_output(self->pin->number);
nrf_gpio_pin_set(self->pin->number);
mp_hal_delay_us(10);
nrf_saadc_resolution_set(NRF_SAADC_RESOLUTION_14BIT);
nrf_saadc_oversample_set(NRF_SAADC_OVERSAMPLE_DISABLED);
nrf_saadc_enable();
// set pad back to an input and take some samples
for (uint32_t i = 0; i < NRF_SAADC_CHANNEL_COUNT; i++)
nrf_saadc_channel_input_set(i, NRF_SAADC_INPUT_DISABLED, NRF_SAADC_INPUT_DISABLED);
nrf_gpio_cfg_input(self->pin->number, NRF_GPIO_PIN_NOPULL);
nrf_saadc_channel_init(CHANNEL_NO, &config);
nrf_saadc_buffer_init(samples, N_SAMPLES);
// 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(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();
nrf_saadc_channel_input_set(CHANNEL_NO, self->pin->adc_channel, self->pin->adc_channel);
nrf_saadc_task_trigger(NRF_SAADC_TASK_START);
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? 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);
nrf_saadc_event_clear(NRF_SAADC_EVENT_DONE);
while(nrf_gpio_pin_read(self->pin->number)) {
if (ticks >= TIMEOUT_US) return TIMEOUT_US;
ticks++;
mp_hal_delay_us(1);
}
}
__enable_irq();
nrf_saadc_task_trigger(NRF_SAADC_TASK_STOP);
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 (to minimize leakage currents)
nrf_gpio_pin_clear(self->pin->number);
nrf_saadc_channel_input_set(CHANNEL_NO, NRF_SAADC_INPUT_DISABLED, NRF_SAADC_INPUT_DISABLED);
nrf_saadc_disable();
nrf_gpio_cfg_output(self->pin->number);
return process_samples(samples, N_SAMPLES);
return ticks;
}
void common_hal_touchio_touchin_construct(touchio_touchin_obj_t* self,
const mcu_pin_obj_t *pin) {
if (!pin->adc_channel) {
mp_raise_ValueError(translate("Invalid pin"));
}
self->pin = pin;
claim_pin(pin);
}