STM32F4: rcc: added rcc_getPeriphClock function

Added function to retrieve the clock frequency of the bus a peripheral is
attached to, given its base address. The function is C++ only and relies
on constexpr mechanism to have zero memory footprint.

platform/mcu/STM32F4xx/drivers/rcc.h

@@ -22,6 +22,7 @@
 #ifndef RCC_H
 #define RCC_H
 
+#include <hwconfig.h>
 #include <stdint.h>
 
 #ifdef __cplusplus
@@ -50,6 +51,34 @@ uint32_t rcc_getBusClock(const uint8_t bus);
 
 #ifdef __cplusplus
 }
+
+/**
+ * Get the clock frequency of the bus a peripheral is attached to.
+ *
+ * @param periph: peripheral base address
+ * @return bus clock frequency in Hz or zero in case of errors.
+ */
+static constexpr uint32_t rcc_getPeriphClock(const void *periph)
+{
+    uint32_t addr = reinterpret_cast<uint32_t>(periph);
+
+    switch(addr & 0xFFFF0000) {
+        case APB1PERIPH_BASE:
+            return rcc_getBusClock(PERIPH_BUS_APB1);
+            break;
+
+        case APB2PERIPH_BASE:
+            return rcc_getBusClock(PERIPH_BUS_APB2);
+            break;
+
+        case AHB1PERIPH_BASE:
+        case AHB2PERIPH_BASE:
+            return rcc_getBusClock(PERIPH_BUS_AHB);
+            break;
+    }
+
+    return 0;
+}
 #endif
 
 #endif /* RCC_H */