Change platform macro to STM32F4, initialize RNG peripheral before use

impl/random.h

@@ -23,7 +23,7 @@ static TLS struct {
 # include "random/mbed.h"
 #elif defined(RIOT_VERSION)
 # include "random/riot.h"
-#elif defined(STM32)
+#elif defined(STM32F4)
 # include "random/stm32.h"
 #else
 #error Unsupported platform

impl/random/stm32.h

@@ -1,7 +1,10 @@
 
-// Requires RNG to be active
+// Use hardware RNG peripheral
+// Working with HAL, LL Driver (untested)
 
-#include "rng.h"
+#ifdef STM32F4
+
+#include "stm32f4xx.h"
 
 static int
 hydro_random_init(void)
@@ -10,16 +13,26 @@ hydro_random_init(void)
     hydro_hash_state st;
     uint16_t         ebits = 0;
 
+    __IO uint32_t tmpreg;
+
+    // Enable RNG clock source
+    SET_BIT(RCC->AHB2ENR, RCC_AHB2ENR_RNGEN);
+
+    // Delay after an RCC peripheral clock enabling
+    tmpreg = READ_BIT(RCC->AHB2ENR, RCC_AHB2ENR_RNGEN);
+    UNUSED(tmpreg);
+
+    // RNG Peripheral enable
+    SET_BIT(RNG->CR, RNG_CR_RNGEN);
+
     hydro_hash_init(&st, ctx, NULL);
 
     while (ebits < 256) {
-        uint32_t r;
-        if(HAL_OK != HAL_RNG_GenerateRandomNumber(&hrng, &r))
-        {
-        	return -1;
+        while (!(READ_BIT(RNG->SR, RNG_SR_DRDY))) {
         }
 
-        hydro_hash_update(&st, (const uint32_t *) &r, sizeof r);
+        uint32_t r = RNG->DR;
+        hydro_hash_update(&st, (const uint32_t*) &r, sizeof r);
         ebits += 32;
     }
 
@@ -27,4 +40,8 @@ hydro_random_init(void)
     hydro_random_context.counter = ~LOAD64_LE(hydro_random_context.state);
 
     return 0;
-}
+}
+
+#else
+#error SMT32 implementaiton missing!
+#endif