RP2040: enable entropy source

Fixes #437

Author: facchinm

cores/arduino/random_seed.cpp

@@ -0,0 +1,17 @@
+#if defined(MBEDTLS_ENTROPY_NV_SEED)
+
+#include "mbed.h"
+
+// Provide stubs for mbedtls entropy source
+// The functions may be implemented using a crypto chip like ECCx08
+extern "C" {
+	WEAK int mbedtls_platform_std_nv_seed_read( unsigned char *buf, size_t buf_len ) {
+		return -1;
+	}
+
+	WEAK int mbedtls_platform_std_nv_seed_write( unsigned char *buf, size_t buf_len ) {
+		return -1;
+	}
+}
+
+#endif

variants/NANO_RP2040_CONNECT/conf/mbed_app.json

@@ -2,6 +2,7 @@
   "target_overrides": {
     "*": {
       "target.printf_lib": "std",
+      "target.macros_add": [ "MBEDTLS_ENTROPY_NV_SEED" ],
       "platform.stdio-buffered-serial": false,
       "platform.stdio-baud-rate": 115200,
       "platform.default-serial-baud-rate": 115200,

variants/RASPBERRY_PI_PICO/conf/mbed_app.json

@@ -2,6 +2,7 @@
   "target_overrides": {
     "*": {
       "target.printf_lib": "std",
+      "target.macros_add": [ "MBEDTLS_ENTROPY_NV_SEED" ],
       "platform.stdio-buffered-serial": false,
       "platform.stdio-baud-rate": 115200,
       "platform.default-serial-baud-rate": 115200,