Add random to ESP32-S2, fix it on STM32

Author: hierophect

ports/esp32s2/common-hal/os/__init__.c

@@ -30,6 +30,8 @@
 #include "py/objtuple.h"
 #include "py/qstr.h"
 
+#include "esp_system.h"
+
 STATIC const qstr os_uname_info_fields[] = {
     MP_QSTR_sysname, MP_QSTR_nodename,
     MP_QSTR_release, MP_QSTR_version, MP_QSTR_machine
@@ -57,5 +59,15 @@ mp_obj_t common_hal_os_uname(void) {
 }
 
 bool common_hal_os_urandom(uint8_t* buffer, uint32_t length) {
-    return false;
+    uint32_t i = 0;
+    while (i < length) {
+        uint32_t new_random = esp_random();
+        for (int j = 0; j < 4 && i < length; j++) {
+            buffer[i] = new_random & 0xff;
+            i++;
+            new_random >>= 8;
+        }
+    }
+
+    return true;
 }

ports/esp32s2/mpconfigport.mk

@@ -25,7 +25,6 @@ CIRCUITPY_COUNTIO = 0
 
 # These modules are implemented in shared-module/ - they can be included in
 # any port once their prerequisites in common-hal are complete.
-CIRCUITPY_RANDOM = 0          # Requires OS
 CIRCUITPY_USB_MIDI = 0        # Requires USB
 CIRCUITPY_ULAB = 0            # No requirements, but takes extra flash
 

ports/stm/common-hal/os/__init__.c

@@ -77,11 +77,10 @@ bool common_hal_os_urandom(uint8_t *buffer, uint32_t length) {
         uint32_t start = HAL_GetTick();
         //the HAL function has a timeout, but it isn't long enough, and isn't adjustable
         while(!(__HAL_RNG_GET_FLAG(&handle,RNG_FLAG_DRDY)) && ((HAL_GetTick() - start) < RNG_TIMEOUT));
-        //
         if (HAL_RNG_GenerateRandomNumber(&handle, &temp) != HAL_OK) {
             mp_raise_ValueError(translate("Random number generation error"));
         }
-        *buffer = (uint8_t)temp;
+        buffer[i] = (uint8_t)temp;
     }
 
     //shut down the peripheral