Check cache before enabling it

The mbed_sdk_init can be called either during cold boot or during
application boot after bootloader has been executed.
In case the bootloader has already enabled the cache,
is is needed to not enable it again.

Author: bcostm

targets/TARGET_STM/mbed_overrides.c

@@ -35,9 +35,16 @@ void mbed_sdk_init()
     HAL_Init();
 
 #if TARGET_STM32F7
-    // Enable CPU L1-Cache
-    SCB_EnableICache();
-    SCB_EnableDCache();
+    // The mbed_sdk_init can be called either during cold boot or during
+    // application boot after bootloader has been executed.
+    // In case the bootloader has already enabled the cache,
+    // is is needed to not enable it again.
+    if (SCB->CCR & (uint32_t)SCB_CCR_IC_Msk == 0) { // If ICache is disabled
+        SCB_EnableICache();
+    }
+    if (SCB->CCR & (uint32_t)SCB_CCR_DC_Msk == 0) { // If DCache is disabled
+        SCB_EnableDCache();
+    }
 #endif /* TARGET_STM32F7 */
 
     /* Configure the System clock source, PLL Multiplier and Divider factors,