zephyr/drivers/pwm/pwm_nrf5_sw.c

/*
 * Copyright (c) 2017 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <soc.h>

#include "pwm.h"

struct pwm_config {
	NRF_TIMER_Type *timer;
	u8_t gpiote_base;
	u8_t ppi_base;
	u8_t map_size;
};

struct chan_map {
	u32_t pwm;
	u32_t pulse_cycles;
};

struct pwm_data {
	u32_t period_cycles;
	struct chan_map map[];
};

static u32_t pwm_period_check(struct pwm_data *data, u8_t map_size,
				 u32_t pwm, u32_t period_cycles,
				 u32_t pulse_cycles)
{
	u8_t i;

	/* allow 0% and 100% duty cycle, as it does not use PWM. */
	if ((pulse_cycles == 0) || (pulse_cycles == period_cycles)) {
		return 0;
	}

	/* fail if requested period does not match already running period */
	for (i = 0; i < map_size; i++) {
		if ((data->map[i].pwm != pwm) &&
		    (data->map[i].pulse_cycles != 0) &&
		    (period_cycles != data->period_cycles)) {
			return -EINVAL;
		}
	}

	return 0;
}

static u8_t pwm_channel_map(struct pwm_data *data, u8_t map_size,
			       u32_t pwm)
{
	u8_t i;

	/* find pin, if already present */
	for (i = 0; i < map_size; i++) {
		if (pwm == data->map[i].pwm) {
			return i;
		}
	}

	/* find a free entry */
	i = map_size;
	while (i--) {
		if (data->map[i].pulse_cycles == 0) {
			break;
		}
	}

	return i;
}

static int pwm_nrf5_sw_pin_set(struct device *dev, u32_t pwm,
			       u32_t period_cycles, u32_t pulse_cycles)
{
	struct pwm_config *config;
	NRF_TIMER_Type *timer;
	struct pwm_data *data;
	u8_t ppi_index;
	u8_t channel;
	u16_t div;
	u32_t ret;

	config = (struct pwm_config *)dev->config->config_info;
	timer = config->timer;
	data = dev->driver_data;

	/* check if requested period is allowed while other channels are
	 * active.
	 */
	ret = pwm_period_check(data, config->map_size, pwm, period_cycles,
			       pulse_cycles);
	if (ret) {
		return ret;
	}

	/* map pwm pin to GPIOTE config/channel */
	channel = pwm_channel_map(data, config->map_size, pwm);
	if (channel >= config->map_size) {
		return -ENOMEM;
	}

	/* stop timer, if already running */
	timer->TASKS_STOP = 1;

	/* clear GPIOTE config */
	NRF_GPIOTE->CONFIG[config->gpiote_base + channel] = 0;

	/* clear PPI used */
	ppi_index = config->ppi_base + (channel << 1);
	NRF_PPI->CHENCLR = BIT(ppi_index) | BIT(ppi_index + 1);

	/* configure GPIO pin as output */
	NRF_GPIO->DIRSET = BIT(pwm);
	if (pulse_cycles == 0) {
		/* 0% duty cycle, keep pin high (for active low LED) */
		NRF_GPIO->OUTSET = BIT(pwm);

		goto pin_set_pwm_off;
	} else if (pulse_cycles == period_cycles) {
		/* 100% duty cycle, keep pin low (for active low LED) */
		NRF_GPIO->OUTCLR = BIT(pwm);

		goto pin_set_pwm_off;
	} else {
		/* x% duty cycle, start PWM with pin low */
		NRF_GPIO->OUTCLR = BIT(pwm);
	}

	/* TODO: if the assigned NRF_TIMER supports higher bit resolution,
	 * use that info in config struct and setup accordingly.
	 */

	/* calc div, to scale down to fit in 16 bits */
	div = period_cycles >> 16;

	/* setup HF timer in 16MHz frequency */
	timer->MODE = TIMER_MODE_MODE_Timer;
	timer->PRESCALER = 0;
	timer->BITMODE = TIMER_BITMODE_BITMODE_16Bit;
	timer->EVENTS_COMPARE[channel] = 0;
	timer->EVENTS_COMPARE[config->map_size] = 0;
	/* TODO: set shorts according to map_size if not 3, i.e. if NRF_TIMER
	 * supports more than 4 compares, then more channels can be supported.
	 */
	timer->SHORTS = TIMER_SHORTS_COMPARE3_CLEAR_Msk;
	timer->CC[channel] = pulse_cycles >> div;
	timer->CC[config->map_size] = period_cycles >> div;
	timer->TASKS_CLEAR = 1;

	/* configure GPIOTE, toggle with initialise output low */
	NRF_GPIOTE->CONFIG[config->gpiote_base + channel] = 0x00030003 |
							    (pwm << 8);

	/* setup PPI */
	NRF_PPI->CH[ppi_index].EEP = (u32_t)
				     &(timer->EVENTS_COMPARE[channel]);
	NRF_PPI->CH[ppi_index].TEP = (u32_t)
				     &(NRF_GPIOTE->TASKS_OUT[channel]);
	NRF_PPI->CH[ppi_index + 1].EEP = (u32_t)
					 &(timer->EVENTS_COMPARE[3]);
	NRF_PPI->CH[ppi_index + 1].TEP = (u32_t)
					 &(NRF_GPIOTE->TASKS_OUT[channel]);
	NRF_PPI->CHENSET = BIT(ppi_index) | BIT(ppi_index + 1);

	/* start timer, hence PWM */
	timer->TASKS_START = 1;

	/* store the pwm/pin and its param */
	data->period_cycles = period_cycles;
	data->map[channel].pwm = pwm;
	data->map[channel].pulse_cycles = pulse_cycles;

	return 0;

pin_set_pwm_off:
	data->map[channel].pulse_cycles = 0;

	return 0;
}

static int pwm_nrf5_sw_get_cycles_per_sec(struct device *dev, u32_t pwm,
					  u64_t *cycles)
{
	struct pwm_config *config;

	config = (struct pwm_config *)dev->config->config_info;

	/* HF timer frequency is derived from 16MHz source and prescaler is 0 */
	*cycles = 16 * 1024 * 1024;

	return 0;
}

static const struct pwm_driver_api pwm_nrf5_sw_drv_api_funcs = {
	.pin_set = pwm_nrf5_sw_pin_set,
	.get_cycles_per_sec = pwm_nrf5_sw_get_cycles_per_sec,
};

static int pwm_nrf5_sw_init(struct device *dev)
{
	return 0;
}

#define PWM_0_MAP_SIZE 3
static const struct pwm_config pwm_nrf5_sw_0_config = {
	.timer = NRF_TIMER1,
	.gpiote_base = 0,
	.ppi_base = 8,
	.map_size = PWM_0_MAP_SIZE,
};

#define PWM_0_DATA_SIZE (offsetof(struct pwm_data, map) + \
			 sizeof(struct chan_map) * PWM_0_MAP_SIZE)
static u8_t pwm_nrf5_sw_0_data[PWM_0_DATA_SIZE];

DEVICE_AND_API_INIT(pwm_nrf5_sw_0, CONFIG_PWM_NRF5_SW_0_DEV_NAME,
		    pwm_nrf5_sw_init, pwm_nrf5_sw_0_data, &pwm_nrf5_sw_0_config,
		    POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,
		    &pwm_nrf5_sw_drv_api_funcs);