tests: add periph_qdec test

* Test all QDEC devices

Signed-off-by: Gilles DOFFE <g.doffe@gmail.com>

tests/periph_qdec/Makefile

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+BOARD ?= nucleo-f401
+include ../Makefile.tests_common
+
+FEATURES_REQUIRED = periph_qdec
+
+USEMODULE += xtimer
+
+include $(RIOTBASE)/Makefile.include

tests/periph_qdec/README.md

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+Expected result
+===============
+If everything is running as supposed to, you should see a X4 mode quadrature decoding on each qdec configured.
+
+Background
+==========
+Test for the low-level QDEC driver.

tests/periph_qdec/main.c

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+/*
+ * Copyright (C) 2017 Gilles DOFFE <gdoffe@gmail.com>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup tests
+ * @{
+ *
+ * @file
+ * @brief       Test for low-level QDEC drivers
+ *
+ * This test initializes all declared QDEC devices.
+ * It displays QDEC counters value each second.
+ *
+ * @author      Gilles DOFFE <gdoffe@gmail.com>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+
+#include "periph/qdec.h"
+#include "xtimer.h"
+
+void handler(void *arg)
+{
+    qdec_t qdec = (qdec_t)arg;
+    printf("QDEC %u counter overflow : reset counter\n", qdec);
+    qdec_read_and_reset(QDEC_DEV(qdec));
+}
+
+int main(void)
+{
+    uint32_t i = 0;
+    int32_t value = 0;
+    puts("Welcome into Quadrature Decoder (QDEC) test program.");
+    puts("This program will count pulses on all available QDEC channels");
+    puts("Written for nucleo-f401, you have to plug signals A and B as follow :");
+    puts("  QDEC0 : signal A on PA6 and signal B on PA7");
+    puts("  QDEC1 : signal A on PB6 and signal B on PB7");
+    puts("Quadrature decoding mode is set to X4 : counting on all edges on both signals");
+
+    for (i = 0; i < QDEC_NUMOF; i++) {
+        int32_t error = qdec_init(QDEC_DEV(i), QDEC_X4, handler, (void *)i);
+        if (error) {
+            fprintf(stderr,"Not supported mode !\n");
+            return error;
+        }
+    }
+
+    while (1) {
+        for (i = 0; i < QDEC_NUMOF; i++) {
+            value = qdec_read_and_reset(QDEC_DEV(i));
+            printf("QDEC %lu = %ld\n", (unsigned long int)i, (long int)value);
+        }
+        xtimer_sleep(1);
+    }
+
+    return 0;
+}