ESP32 Hardware Timer Interrupt
In ESP32-IDF < v5.0, we can only use the driver/timer.h:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/queue.h"
#include "driver/gpio.h"
#include "driver/dac.h"
#include "driver/timer.h"
#include "esp_log.h"
/* The timer ISR has an execution time of 5.5 micro-seconds(us).
Therefore, a timer period less than 5.5 us will cause trigger the interrupt watchdog.
7 us is a safe interval that will not trigger the watchdog. No need to customize it.
*/
#define WITH_RELOAD 1
#define TIMER_INTR_US 7 // Execution time of each ISR interval in micro-seconds
#define TIMER_DIVIDER 16
#define POINT_ARR_LEN 200 // Length of points array
#define AMP_DAC 255 // Amplitude of DAC voltage. If it's more than 256 will causes dac_output_voltage() output 0.
#define VDD 3300 // VDD is 3.3V, 3300mV
#define CONST_PERIOD_2_PI 6.2832
#define SEC_TO_MICRO_SEC(x) ((x) / 1000 / 1000) // Convert second to micro-second
#define UNUSED_PARAM __attribute__((unused)) // A const period parameter which equals 2 * pai, used to calculate raw dac output value.
#define TIMER_TICKS (TIMER_BASE_CLK / TIMER_DIVIDER) // TIMER_BASE_CLK = APB_CLK = 80MHz
#define ALARM_VAL_US SEC_TO_MICRO_SEC(TIMER_INTR_US * TIMER_TICKS) // Alarm value in micro-seconds
#define OUTPUT_POINT_NUM (int)(1000000 / (TIMER_INTR_US * FREQ) + 0.5) // The number of output wave points.
#define DAC_CHAN CONFIG_EXAMPLE_DAC_CHANNEL // DAC_CHANNEL_1 (GPIO25) by default
#define FREQ CONFIG_EXAMPLE_WAVE_FREQUENCY // 3kHz by default
_Static_assert(OUTPUT_POINT_NUM <= POINT_ARR_LEN, "The CONFIG_EXAMPLE_WAVE_FREQUENCY is too low and using too long buffer.");
static int raw_val[POINT_ARR_LEN]; // Used to store raw values
static int volt_val[POINT_ARR_LEN]; // Used to store voltage values(in mV)
static const char *TAG = "wave_gen";
static int g_index = 0;
/* Timer interrupt service routine */
static void IRAM_ATTR timer0_ISR(void *ptr)
{
timer_group_clr_intr_status_in_isr(TIMER_GROUP_0, TIMER_0);
timer_group_enable_alarm_in_isr(TIMER_GROUP_0, TIMER_0);
int *head = (int*)ptr;
/* DAC output ISR has an execution time of 4.4 us*/
if (g_index >= OUTPUT_POINT_NUM) g_index = 0;
dac_output_voltage(DAC_CHAN, *(head + g_index));
g_index++;
}
/* Timer group0 TIMER_0 initialization */
static void example_timer_init(int timer_idx, bool auto_reload)
{
esp_err_t ret;
timer_config_t config = {
.divider = TIMER_DIVIDER,
.counter_dir = TIMER_COUNT_UP,
.counter_en = TIMER_PAUSE,
.alarm_en = TIMER_ALARM_EN,
.intr_type = TIMER_INTR_LEVEL,
.auto_reload = auto_reload,
};
ret = timer_init(TIMER_GROUP_0, timer_idx, &config);
ESP_ERROR_CHECK(ret);
ret = timer_set_counter_value(TIMER_GROUP_0, timer_idx, 0x00000000ULL);
ESP_ERROR_CHECK(ret);
ret = timer_set_alarm_value(TIMER_GROUP_0, timer_idx, ALARM_VAL_US);
ESP_ERROR_CHECK(ret);
ret = timer_enable_intr(TIMER_GROUP_0, TIMER_0);
ESP_ERROR_CHECK(ret);
/* Register an ISR handler */
timer_isr_register(TIMER_GROUP_0, timer_idx, timer0_ISR, (void *)raw_val, 0, NULL);
}
static void prepare_data(int pnt_num)
{
timer_pause(TIMER_GROUP_0, TIMER_0);
for (int i = 0; i < pnt_num; i ++) {
#ifdef CONFIG_EXAMPLE_WAVEFORM_SINE
raw_val[i] = (int)((sin( i * CONST_PERIOD_2_PI / pnt_num) + 1) * (double)(AMP_DAC)/2 + 0.5);
#elif CONFIG_EXAMPLE_WAVEFORM_TRIANGLE
raw_val[i] = (i > (pnt_num/2)) ? (2 * AMP_DAC * (pnt_num - i) / pnt_num) : (2 * AMP_DAC * i / pnt_num);
#elif CONFIG_EXAMPLE_WAVEFORM_SAWTOOTH
raw_val[i] = (i == pnt_num) ? 0 : (i * AMP_DAC / pnt_num);
#elif CONFIG_EXAMPLE_WAVEFORM_SQUARE
raw_val[i] = (i < (pnt_num/2)) ? AMP_DAC : 0;
#endif
volt_val[i] = (int)(VDD * raw_val[i] / (float)AMP_DAC);
}
timer_start(TIMER_GROUP_0, TIMER_0);
}
static void log_info(void)
{
ESP_LOGI(TAG, "DAC output channel: %d", DAC_CHAN);
if (DAC_CHAN == DAC_CHANNEL_1) {
ESP_LOGI(TAG, "GPIO:%d", GPIO_NUM_25);
} else {
ESP_LOGI(TAG, "GPIO:%d", GPIO_NUM_26);
}
#ifdef CONFIG_EXAMPLE_WAVEFORM_SINE
ESP_LOGI(TAG, "Waveform: SINE");
#elif CONFIG_EXAMPLE_WAVEFORM_TRIANGLE
ESP_LOGI(TAG, "Waveform: TRIANGLE");
#elif CONFIG_EXAMPLE_WAVEFORM_SAWTOOTH
ESP_LOGI(TAG, "Waveform: SAWTOOTH");
#elif CONFIG_EXAMPLE_WAVEFORM_SQUARE
ESP_LOGI(TAG, "Waveform: SQUARE");
#endif
ESP_LOGI(TAG, "Frequency(Hz): %d", FREQ);
ESP_LOGI(TAG, "Output points num: %d\n", OUTPUT_POINT_NUM);
}
void app_main(void)
{
esp_err_t ret;
example_timer_init(TIMER_0, WITH_RELOAD);
ret = dac_output_enable(DAC_CHAN);
ESP_ERROR_CHECK(ret);
log_info();
g_index = 0;
prepare_data(OUTPUT_POINT_NUM);
while(1) {
vTaskDelay(10);
#if CONFIG_EXAMPLE_LOG_VOLTAGE
if (g_index < OUTPUT_POINT_NUM) {
ESP_LOGI(TAG, "Output voltage(mV): %d", volt_val[g_index]);
ESP_LOGD(TAG, "g_index: %d\n", g_index);
}
#endif
}
}
After ESP-IDF v5.0:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/queue.h"
#include "driver/gpio.h"
#include "driver/dac.h"
#include "driver/gptimer.h"
#include "esp_log.h"
/* The timer ISR has an execution time of 5.5 micro-seconds(us).
Therefore, a timer period less than 5.5 us will cause trigger the interrupt watchdog.
7 us is a safe interval that will not trigger the watchdog. No need to customize it.
*/
#define TIMER_INTR_US 7 // Execution time of each ISR interval in micro-seconds
#define POINT_ARR_LEN 200 // Length of points array
#define AMP_DAC 255 // Amplitude of DAC voltage. If it's more than 256 will causes dac_output_voltage() output 0.
#define VDD 3300 // VDD is 3.3V, 3300mV
#define CONST_PERIOD_2_PI 6.2832
#define DAC_CHAN CONFIG_EXAMPLE_DAC_CHANNEL // DAC_CHANNEL_1 (GPIO25) by default
#define FREQ CONFIG_EXAMPLE_WAVE_FREQUENCY // 3kHz by default
#define OUTPUT_POINT_NUM (int)(1000000 / (TIMER_INTR_US * FREQ) + 0.5) // The number of output wave points.
_Static_assert(OUTPUT_POINT_NUM <= POINT_ARR_LEN, "The CONFIG_EXAMPLE_WAVE_FREQUENCY is too low and using too long buffer.");
static int raw_val[POINT_ARR_LEN]; // Used to store raw values
static int volt_val[POINT_ARR_LEN]; // Used to store voltage values(in mV)
static const char *TAG = "wave_gen";
static int g_index = 0;
/* Timer interrupt service routine */
static bool IRAM_ATTR on_timer_alarm_cb(gptimer_handle_t timer, const gptimer_alarm_event_data_t *edata, void *user_data)
{
int *head = (int *)user_data;
/* DAC output ISR has an execution time of 4.4 us*/
if (g_index >= OUTPUT_POINT_NUM) {
g_index = 0;
}
dac_output_voltage(DAC_CHAN, *(head + g_index));
g_index++;
return false;
}
static void prepare_data(int pnt_num)
{
for (int i = 0; i < pnt_num; i ++) {
#ifdef CONFIG_EXAMPLE_WAVEFORM_SINE
raw_val[i] = (int)((sin( i * CONST_PERIOD_2_PI / pnt_num) + 1) * (double)(AMP_DAC) / 2 + 0.5);
#elif CONFIG_EXAMPLE_WAVEFORM_TRIANGLE
raw_val[i] = (i > (pnt_num / 2)) ? (2 * AMP_DAC * (pnt_num - i) / pnt_num) : (2 * AMP_DAC * i / pnt_num);
#elif CONFIG_EXAMPLE_WAVEFORM_SAWTOOTH
raw_val[i] = (i == pnt_num) ? 0 : (i * AMP_DAC / pnt_num);
#elif CONFIG_EXAMPLE_WAVEFORM_SQUARE
raw_val[i] = (i < (pnt_num / 2)) ? AMP_DAC : 0;
#endif
volt_val[i] = (int)(VDD * raw_val[i] / (float)AMP_DAC);
}
}
static void log_info(void)
{
ESP_LOGI(TAG, "DAC output channel: %d", DAC_CHAN);
if (DAC_CHAN == DAC_CHANNEL_1) {
ESP_LOGI(TAG, "GPIO:%d", GPIO_NUM_25);
} else {
ESP_LOGI(TAG, "GPIO:%d", GPIO_NUM_26);
}
#ifdef CONFIG_EXAMPLE_WAVEFORM_SINE
ESP_LOGI(TAG, "Waveform: SINE");
#elif CONFIG_EXAMPLE_WAVEFORM_TRIANGLE
ESP_LOGI(TAG, "Waveform: TRIANGLE");
#elif CONFIG_EXAMPLE_WAVEFORM_SAWTOOTH
ESP_LOGI(TAG, "Waveform: SAWTOOTH");
#elif CONFIG_EXAMPLE_WAVEFORM_SQUARE
ESP_LOGI(TAG, "Waveform: SQUARE");
#endif
ESP_LOGI(TAG, "Frequency(Hz): %d", FREQ);
ESP_LOGI(TAG, "Output points num: %d\n", OUTPUT_POINT_NUM);
}
void app_main(void)
{
g_index = 0;
gptimer_handle_t gptimer = NULL;
gptimer_config_t timer_config = {
.clk_src = GPTIMER_CLK_SRC_APB,
.direction = GPTIMER_COUNT_UP,
.resolution_hz = 1000000, // 1MHz, 1 tick = 1us
};
ESP_ERROR_CHECK(gptimer_new_timer(&timer_config, &gptimer));
ESP_ERROR_CHECK(dac_output_enable(DAC_CHAN));
log_info();
prepare_data(OUTPUT_POINT_NUM);
gptimer_alarm_config_t alarm_config = {
.reload_count = 0,
.alarm_count = TIMER_INTR_US,
.flags.auto_reload_on_alarm = true,
};
gptimer_event_callbacks_t cbs = {
.on_alarm = on_timer_alarm_cb,
};
ESP_ERROR_CHECK(gptimer_register_event_callbacks(gptimer, &cbs, raw_val));
ESP_ERROR_CHECK(gptimer_set_alarm_action(gptimer, &alarm_config));
ESP_ERROR_CHECK(gptimer_start(gptimer));
while (1) {
vTaskDelay(10);
#if CONFIG_EXAMPLE_LOG_VOLTAGE
if (g_index < OUTPUT_POINT_NUM) {
ESP_LOGI(TAG, "Output voltage(mV): %d", volt_val[g_index]);
ESP_LOGD(TAG, "g_index: %d\n", g_index);
}
#endif
}
}