WiFi scan example (#265)

examples/wifi_scan/Makefile

@@ -0,0 +1,4 @@
+PROGRAM = wifi_scan
+#ESPBAUD = 460800
+
+include ../../common.mk

examples/wifi_scan/main.c

@@ -0,0 +1,72 @@
+/*
+ * WiFi scan
+ *
+ * Part of esp-open-rtos
+ * Copyright (C) 2016 Ruslan V. Uss <unclerus@gmail.com>
+ * BSD Licensed as described in the file LICENSE
+ */
+#include <esp/uart.h>
+#include <stdio.h>
+#include <espressif/esp_common.h>
+#include <FreeRTOS.h>
+#include <task.h>
+#include <string.h>
+
+static const char * const auth_modes [] = {
+    [AUTH_OPEN]         = "Open",
+    [AUTH_WEP]          = "WEP",
+    [AUTH_WPA_PSK]      = "WPA/PSK",
+    [AUTH_WPA2_PSK]     = "WPA2/PSK",
+    [AUTH_WPA_WPA2_PSK] = "WPA/WPA2/PSK"
+};
+
+static void scan_done_cb(void *arg, sdk_scan_status_t status)
+{
+    char ssid[33]; // max SSID length + zero byte
+
+    if (status != SCAN_OK)
+    {
+        printf("Error: WiFi scan failed\n");
+        return;
+    }
+
+    struct sdk_bss_info *bss = (struct sdk_bss_info *)arg;
+    // first one is invalid
+    bss = bss->next.stqe_next;
+
+    printf("\n----------------------------------------------------------------------------------\n");
+    printf("                             Wi-Fi networks\n");
+    printf("----------------------------------------------------------------------------------\n");
+
+    while (NULL != bss)
+    {
+        size_t len = strlen((const char *)bss->ssid);
+        memcpy(ssid, bss->ssid, len);
+        ssid[len] = 0;
+
+        printf("%32s (" MACSTR ") RSSI: %02d, security: %s\n", ssid,
+            MAC2STR(bss->bssid), bss->rssi, auth_modes[bss->authmode]);
+
+        bss = bss->next.stqe_next;
+    }
+}
+
+static void scan_task(void *arg)
+{
+    while (true)
+    {
+        sdk_wifi_station_scan(NULL, scan_done_cb);
+        vTaskDelay(5000 / portTICK_PERIOD_MS);
+    }
+}
+
+void user_init()
+{
+    uart_set_baud(0, 115200);
+    printf("SDK version:%s\n\n", sdk_system_get_sdk_version());
+
+    // We can scan only in station mode
+    sdk_wifi_set_opmode(STATION_MODE);
+
+    xTaskCreate(scan_task, "scan", 512, NULL, 2, NULL);
+}