Initial HW PWM (Delta-Sigma) (#609)

examples/dsm_test/Makefile

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+# Simple makefile for simple example
+PROGRAM=dsm_test
+EXTRA_COMPONENTS = extras/dsm
+include ../../common.mk

examples/dsm_test/dsm_test.c

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+/* Very basic example to test the dsm library
+ * Led intensity from module will change over time.
+ *
+ * Part of esp-open-rtos
+ * Copyright (C) 2018 zaltora (https://github.com/Zaltora)
+ * BSD Licensed as described in the file LICENSE
+ */
+#include "espressif/esp_common.h"
+#include "esp/uart.h"
+#include "FreeRTOS.h"
+#include "task.h"
+#include "dsm.h"
+
+#define TEST_WITH_160MHZ (0)
+#define DSM_PIN          (2)
+
+void task1(void *pvParameters)
+{
+    uint32_t const init_count = 0;
+    uint32_t count = init_count;
+    while(1)
+    {
+        vTaskDelay(100/portTICK_PERIOD_MS);
+        printf("Target set to %3u, ", count);
+        //Freq = (80,000,000/prescale) * (target / 256) HZ           (0   < target < 128)
+        //Freq = (80,000,000/prescale) * ((256 - target) / 256)  HZ  (128 < target < 256)
+        if (count < 128)
+        {
+           printf("Freqency: %.1f Hz\r\n", (80000000.0/255.0 * (count/ 256.0)));
+        }
+        else
+        {
+            printf("Freqency: %.1f Hz\r\n", 80000000.0/255.0 * ((256.0-count)/ 256.0));
+        }
+        dsm_set_target(count);
+        count++;
+        if (count > UINT8_MAX)
+            count = init_count;
+    }
+}
+
+void user_init(void)
+{
+    uint8_t pins[1];
+    uart_set_baud(0, 115200);
+
+#if (TEST_WITH_160MHZ)
+    sdk_system_update_cpu_freq(160);
+#endif
+
+    printf("SDK version:%s\r\n", sdk_system_get_sdk_version());
+
+    pins[0] = DSM_PIN;
+
+    /* register pin to use with DSM */
+    dsm_init(1, pins);
+    /* Set prescale to FF to get a proper signal */
+    dsm_set_prescale(0xFF);
+    /* Target initial */
+    dsm_set_target(0);
+    /* start dsm to pin */
+    dsm_start();
+
+    printf("dsm start\r\n");
+
+    xTaskCreate(task1, "tsk1", 256, NULL, 2, NULL);
+}