boards/stm32: introduce common default rtt config

boards/common/stm32/include/cfg_rtt_default.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2019 Inria
+ *
+ * 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     boards_common_stm32
+ * @{
+ *
+ * @file
+ * @brief       Common configuration for STM32 RTT
+ *
+ * @author      Alexandre Abadie <alexandre.abadie@inria.fr>
+ */
+
+#ifndef CFG_RTT_DEFAULT_H
+#define CFG_RTT_DEFAULT_H
+
+#include "periph_cpu.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @name    RTT configuration
+ *
+ * On the STM32Lx platforms, we always utilize the LPTIM1.
+ * @{
+ */
+#define RTT_NUMOF           (1)
+#define RTT_FREQUENCY       (1024U)             /* 32768 / 2^n */
+#define RTT_MAX_VALUE       (0x0000ffff)        /* 16-bit timer */
+/** @} */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CFG_RTT_DEFAULT_H */
+/** @} */