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diff --git a/libmaple/rcc.c b/libmaple/rcc.c
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+/******************************************************************************
+ * The MIT License
+ *
+ * Copyright (c) 2010 Perry Hung.
+ * Copyright (c) 2011 LeafLabs, LLC.
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy,
+ * modify, merge, publish, distribute, sublicense, and/or sell copies
+ * of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *****************************************************************************/
+
+/**
+ * @file libmaple/rcc.c
+ * @brief Portable RCC routines.
+ */
+
+#include <libmaple/rcc.h>
+
+#include "rcc_private.h"
+
+/**
+ * @brief Get a peripheral's clock domain
+ * @param id Clock ID of the peripheral whose clock domain to return
+ * @return Clock source for the given clock ID
+ */
+rcc_clk_domain rcc_dev_clk(rcc_clk_id id) {
+    return rcc_dev_table[id].clk_domain;
+}
+
+/**
+ * @brief Switch the clock used as the source of the system clock.
+ *
+ * After switching the source, this function blocks until the new
+ * clock source is in use.
+ *
+ * @param sysclk_src New system clock source.
+ * @see rcc_sysclk_src
+ */
+void rcc_switch_sysclk(rcc_sysclk_src sysclk_src) {
+    uint32 cfgr = RCC_BASE->CFGR;
+    cfgr &= ~RCC_CFGR_SW;
+    cfgr |= sysclk_src;
+
+    /* Switch SYSCLK source. */
+    RCC_BASE->CFGR = cfgr;
+
+    /* Wait for new source to come into use. */
+    while ((RCC_BASE->CFGR & RCC_CFGR_SWS) != (sysclk_src << 2))
+        ;
+}
+
+/*
+ * Turning clocks off and on, querying their status.
+ */
+
+/* IMPORTANT NOTE FOR IMPLEMENTORS:
+ *
+ * libmaple assumes that enum rcc_clk enumerators are two-byte
+ * values, stored in a uint16, in the following way:
+ *
+ *  - The high-order byte is the byte offset (from RCC_BASE) of the register
+ *    to touch when turning on or off the given clock.
+ *
+ *  - The low-order byte is the bit in that register that turns the
+ *    clock on or off.
+ *
+ * Example for STM32F1: Turning on the high-speed external clock (HSE)
+ * involves setting HSEON, bit 16, of RCC_CR. The high-order byte is
+ * then offsetof(struct rcc_reg_map, CR) = 0, and the low-order byte
+ * is 16.
+ *
+ * The corresponding value of RCC_CLK_HSE is thus (0 << 8) | 16 = 16.
+ *
+ * On all known STM32 series, this encoding has the property that
+ * adding one to the low byte also gives the bit to check to determine
+ * if the clock is ready. For example, on STM32F1, RCC_CR_HSERDY is
+ * bit 17. If that's not the case on your series, rcc_is_clk_ready()
+ * won't work for you. */
+
+/* Returns the RCC register which controls the clock source. */
+static inline __io uint32* rcc_clk_reg(rcc_clk clock) {
+    return (__io uint32*)((__io uint8*)RCC_BASE + (clock >> 8));
+}
+
+/* Returns a mask in rcc_clk_reg(clock) to be used for turning the
+ * clock on and off */
+static inline uint32 rcc_clk_on_mask(rcc_clk clock) {
+    return 1 << (clock & 0xFF);
+}
+
+/* Returns a mask in rcc_clk_reg(clock) to be used when checking the
+ * readiness of the clock. */
+static inline uint32 rcc_clk_ready_mask(rcc_clk clock) {
+    return rcc_clk_on_mask(clock) << 1;
+}
+
+/**
+ * @brief Turn on a clock source.
+ *
+ * After this routine exits, callers should ensure that the clock
+ * source is ready by waiting until rcc_is_clk_ready(clock) returns
+ * true.
+ *
+ * @param clock Clock to turn on.
+ * @see rcc_turn_off_clk()
+ * @see rcc_is_clk_ready()
+ */
+void rcc_turn_on_clk(rcc_clk clock) {
+    *rcc_clk_reg(clock) |= rcc_clk_on_mask(clock);
+}
+
+/**
+ * @brief Turn off a clock source.
+ *
+ * In certain configurations, certain clock sources cannot be safely
+ * turned off. (For example, the main PLL on STM32F1 devices cannot be
+ * turned off if it has been selected as the SYSCLK source). Consult
+ * the reference material for your MCU to ensure it is safe to call
+ * this function.
+ *
+ * @param clock Clock to turn off.
+ * @see rcc_turn_on_clk()
+ * @see rcc_is_clk_ready()
+ */
+void rcc_turn_off_clk(rcc_clk clock) {
+    *rcc_clk_reg(clock) &= ~rcc_clk_on_mask(clock);
+}
+
+/**
+ * @brief Check if a clock is on.
+ * @param clock Clock to check.
+ * @return 1 if the clock is on, 0 if the clock is off.
+ */
+int rcc_is_clk_on(rcc_clk clock) {
+    return !!(*rcc_clk_reg(clock) & rcc_clk_on_mask(clock));
+}
+
+/**
+ * @brief Check if a clock source is ready.
+ *
+ * In general, it is not safe to rely on a clock source unless this
+ * function returns nonzero. Also note that this function may return
+ * nonzero for a short period of time after a clock has been turned
+ * off. Consult the reference material for your MCU for more details.
+ *
+ * @param clock Clock whose readiness to check for.
+ * @return Nonzero if the clock is ready, zero otherwise.
+ * @see rcc_turn_on_clk()
+ * @see rcc_turn_off_clk()
+ */
+int rcc_is_clk_ready(rcc_clk clock) {
+    return (int)(*rcc_clk_reg(clock) & rcc_clk_ready_mask(clock));
+}