stm32/rng: Simplify RNG implementation by accessing raw peripheral regs.

It saves code size and RAM, and is more efficient to execute.

ports/stm32/Makefile

@@ -265,7 +265,6 @@ SRC_HAL = $(addprefix $(HAL_DIR)/Src/stm32$(MCU_SERIES)xx_,\
 	hal_pwr_ex.c \
 	hal_rcc.c \
 	hal_rcc_ex.c \
-	hal_rng.c \
 	hal_rtc.c \
 	hal_rtc_ex.c \
 	hal_sd.c \

ports/stm32/main.c

@@ -552,10 +552,6 @@ soft_reset:
     can_init0();
 #endif
 
-#if MICROPY_HW_ENABLE_RNG
-    rng_init0();
-#endif
-
     #if MICROPY_HW_ENABLE_HW_I2C
     i2c_init0();
     #endif

ports/stm32/rng.c

@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2013, 2014 Damien P. George
+ * Copyright (c) 2013-2018 Damien P. George
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -24,44 +24,35 @@
  * THE SOFTWARE.
  */
 
-#include <string.h>
-
-#include "py/obj.h"
 #include "rng.h"
 
 #if MICROPY_HW_ENABLE_RNG
 
-/// \moduleref pyb
+#define RNG_TIMEOUT_MS (10)
-
-STATIC RNG_HandleTypeDef RNGHandle = {.Instance = NULL};
-
-void rng_init0(void) {
-    // reset the RNG handle
-    memset(&RNGHandle, 0, sizeof(RNG_HandleTypeDef));
-    RNGHandle.Instance = RNG;
-}
-
-void rng_init(void) {
-    __RNG_CLK_ENABLE();
-    HAL_RNG_Init(&RNGHandle);
-}
 
 uint32_t rng_get(void) {
-    if (RNGHandle.State == HAL_RNG_STATE_RESET) {
+    // Enable the RNG peripheral if it's not already enabled
-        rng_init();
+    if (!(RNG->CR & RNG_CR_RNGEN)) {
-    }
+        __HAL_RCC_RNG_CLK_ENABLE();
-    return HAL_RNG_GetRandomNumber(&RNGHandle);
+        RNG->CR |= RNG_CR_RNGEN;
     }
 
-/// \function rng()
+    // Wait for a new random number to be ready, takes on the order of 10us
-/// Return a 30-bit hardware generated random number.
+    uint32_t start = HAL_GetTick();
+    while (!(RNG->SR & RNG_SR_DRDY)) {
+        if (HAL_GetTick() - start >= RNG_TIMEOUT_MS) {
+            return 0;
+        }
+    }
+
+    // Get and return the new random number
+    return RNG->DR;
+}
+
+// Return a 30-bit hardware generated random number.
 STATIC mp_obj_t pyb_rng_get(void) {
-    if (RNGHandle.State == HAL_RNG_STATE_RESET) {
+    return mp_obj_new_int(rng_get() >> 2);
-        rng_init();
 }
-    return mp_obj_new_int(HAL_RNG_GetRandomNumber(&RNGHandle) >> 2);
-}
-
 MP_DEFINE_CONST_FUN_OBJ_0(pyb_rng_get_obj, pyb_rng_get);
 
 #endif // MICROPY_HW_ENABLE_RNG

ports/stm32/rng.h

@@ -26,7 +26,8 @@
 #ifndef MICROPY_INCLUDED_STMHAL_RNG_H
 #define MICROPY_INCLUDED_STMHAL_RNG_H
 
-void rng_init0(void);
+#include "py/obj.h"
+
 uint32_t rng_get(void);
 
 MP_DECLARE_CONST_FUN_OBJ_0(pyb_rng_get_obj);