cpu/esp8266: add CPU frequency selection to Kconfig

cpu/esp8266/Kconfig

@@ -64,6 +64,22 @@ config CPU_MODEL
 config CPU
     default "esp8266" if CPU_FAM_ESP8266
 
+menu "ESP8266 specific configurations"
+    depends on TEST_KCONFIG
+    depends on HAS_ARCH_ESP8266
+
+    choice
+        bool "CPU clock frequency"
+        default ESP8266_CPU_FREQUENCY_80
+
+        config ESP8266_CPU_FREQUENCY_80
+            bool "80 MHz"
+        config ESP8266_CPU_FREQUENCY_160
+            bool "160 MHz"
+    endchoice
+
+endmenu
+
 source "$(RIOTCPU)/esp_common/Kconfig"
 
 config MODULE_ESP_I2C_SW

cpu/esp8266/include/cpu_conf.h

@@ -33,6 +33,16 @@ extern "C" {
 * @name    Clock configuration
 * @{
 */
+
+#ifndef DOXYGEN
+/* Mapping of Kconfig defines to the respective enumeration values */
+#if CONFIG_ESP8266_CPU_FREQUENCY_80
+#define ESP8266_CPU_FREQUENCY   80
+#elif CONFIG_ESP8266_CPU_FREQUENCY_160
+#define ESP8266_CPU_FREQUENCY   160
+#endif
+#endif
+
 /**
  * @brief   Defines the CPU frequency in MHz
  *
@@ -41,6 +51,10 @@ extern "C" {
 #ifndef ESP8266_CPU_FREQUENCY
 #define ESP8266_CPU_FREQUENCY   (80)
 #endif
+
+/**
+ * @brief   Mapping configured ESP8266 default clock to CLOCK_CORECLOCK define
+ */
 #define CLOCK_CORECLOCK         (1000000UL * ESP8266_CPU_FREQUENCY)
 /** @} */