diff --git a/features/mbedtls/targets/TARGET_NUVOTON/TARGET_M480/aes/aes_alt.c b/features/mbedtls/targets/TARGET_NUVOTON/TARGET_M480/aes/aes_alt.c
index 725f95c58f..855d415f78 100644
--- a/features/mbedtls/targets/TARGET_NUVOTON/TARGET_M480/aes/aes_alt.c
+++ b/features/mbedtls/targets/TARGET_NUVOTON/TARGET_M480/aes/aes_alt.c
@@ -176,17 +176,9 @@ static void __nvt_aes_crypt( mbedtls_aes_context *ctx,
 
     AES_SetDMATransfer(0, (uint32_t)pIn, (uint32_t)pOut, dataSize);
 
-    g_AES_done = 0;
-    /* Ensure memory accesses above are completed before DMA is started
-     *
-     * Replacing __DSB() with __DMB() is also OK in this case.
-     *
-     * Refer to "multi-master systems" section with DMA in:
-     * https://static.docs.arm.com/dai0321/a/DAI0321A_programming_guide_memory_barriers_for_m_profile.pdf
-     */
-    __DSB();
+    crypto_aes_prestart();
     AES_Start(0, CRYPTO_DMA_ONE_SHOT);
-    while (!g_AES_done);
+    crypto_aes_wait();
     
     if( pOut != output ) {
         memcpy(output, au8OutputData, dataSize);
diff --git a/features/mbedtls/targets/TARGET_NUVOTON/TARGET_NUC472/aes/aes_alt.c b/features/mbedtls/targets/TARGET_NUVOTON/TARGET_NUC472/aes/aes_alt.c
index 67df8f5425..f8a1c97d5e 100644
--- a/features/mbedtls/targets/TARGET_NUVOTON/TARGET_NUC472/aes/aes_alt.c
+++ b/features/mbedtls/targets/TARGET_NUVOTON/TARGET_NUC472/aes/aes_alt.c
@@ -176,17 +176,9 @@ static void __nvt_aes_crypt( mbedtls_aes_context *ctx,
 
     AES_SetDMATransfer(0, (uint32_t)pIn, (uint32_t)pOut, dataSize);
 
-    g_AES_done = 0;
-    /* Ensure memory accesses above are completed before DMA is started
-     *
-     * Replacing __DSB() with __DMB() is also OK in this case.
-     *
-     * Refer to "multi-master systems" section with DMA in:
-     * https://static.docs.arm.com/dai0321/a/DAI0321A_programming_guide_memory_barriers_for_m_profile.pdf
-     */
-    __DSB();
+    crypto_aes_prestart();
     AES_Start(0, CRYPTO_DMA_ONE_SHOT);
-    while (!g_AES_done);
+    crypto_aes_wait();
     
     if( pOut != output ) {
         memcpy(output, au8OutputData, dataSize);
diff --git a/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.c b/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.c
index 4c4c52d04f..bc7a58a30c 100644
--- a/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.c
+++ b/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.c
@@ -24,9 +24,6 @@
 #include "nu_bitutil.h"
 #include "crypto-misc.h"
 
-volatile int g_PRNG_done;
-volatile int g_AES_done;
-
 /* Track if AES H/W is available */
 static uint16_t crypto_aes_avail = 1;
 /* Track if DES H/W is available */
@@ -40,6 +37,14 @@ static uint16_t crypto_init_counter = 0U;
 static bool crypto_submodule_acquire(uint16_t *submodule_avail);
 static void crypto_submodule_release(uint16_t *submodule_avail);
 
+/* Track if PRNG H/W operation is done */
+static volatile uint16_t crypto_prng_done;
+/* Track if AES H/W operation is done */
+static volatile uint16_t crypto_aes_done;
+
+static void crypto_submodule_prestart(volatile uint16_t *submodule_done);
+static bool crypto_submodule_wait(volatile uint16_t *submodule_done);
+
 /* As crypto init counter changes from 0 to 1:
  *
  * 1. Enable crypto clock
@@ -125,6 +130,26 @@ void crypto_sha_release(void)
     crypto_submodule_release(&crypto_sha_avail);
 }
 
+void crypto_prng_prestart(void)
+{
+    crypto_submodule_prestart(&crypto_prng_done);
+}
+
+bool crypto_prng_wait(void)
+{
+    return crypto_submodule_wait(&crypto_prng_done);
+}
+
+void crypto_aes_prestart(void)
+{
+    crypto_submodule_prestart(&crypto_aes_done);
+}
+
+bool crypto_aes_wait(void)
+{
+    return crypto_submodule_wait(&crypto_aes_done);
+}
+
 bool crypto_dma_buff_compat(const void *buff, size_t buff_size, size_t size_aligned_to)
 {
     uint32_t buff_ = (uint32_t) buff;
@@ -146,14 +171,35 @@ static void crypto_submodule_release(uint16_t *submodule_avail)
     while (! core_util_atomic_cas_u16(submodule_avail, &expectedCurrentValue, 1));
 }
 
+static void crypto_submodule_prestart(volatile uint16_t *submodule_done)
+{
+    *submodule_done = 0;
+    
+    /* Ensure memory accesses above are completed before DMA is started
+     *
+     * Replacing __DSB() with __DMB() is also OK in this case.
+     *
+     * Refer to "multi-master systems" section with DMA in:
+     * https://static.docs.arm.com/dai0321/a/DAI0321A_programming_guide_memory_barriers_for_m_profile.pdf
+     */
+    __DSB();
+}
+
+static bool crypto_submodule_wait(volatile uint16_t *submodule_done)
+{
+    while (! *submodule_done);
+    
+    return true;
+}
+
 /* Crypto interrupt handler */
 void CRYPTO_IRQHandler()
 {
     if (PRNG_GET_INT_FLAG()) {
-        g_PRNG_done = 1;
+        crypto_prng_done = 1;
         PRNG_CLR_INT_FLAG();
     }  else if (AES_GET_INT_FLAG()) {
-        g_AES_done = 1;
+        crypto_aes_done = 1;
         AES_CLR_INT_FLAG();
     }
 }
diff --git a/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.h b/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.h
index 4bee4f644c..bec4a96ba5 100644
--- a/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.h
+++ b/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.h
@@ -23,14 +23,6 @@
 extern "C" {
 #endif
 
-/* Flags to indicate crypto H/W operation has done
- *
- * Crypto driver would clear it before trigger and wait for it. 
- * Crypto interrupt handler would set it on done or error.
- */
-extern volatile int g_PRNG_done;
-extern volatile int g_AES_done;
-
 /* Init/Uninit crypto module */
 void crypto_init(void);
 void crypto_uninit(void);
@@ -54,6 +46,27 @@ void crypto_des_release(void);
 bool crypto_sha_acquire(void);
 void crypto_sha_release(void);
 
+/* Flow control between crypto/xxx start and crypto/xxx ISR 
+ *
+ * crypto_xxx_prestart/crypto_xxx_wait encapsulate control flow between crypto/xxx start and crypto/xxx ISR.
+ * 
+ * crypto_xxx_prestart will also address synchronization issue with memory barrier instruction.
+ *
+ * On finish, return of crypto_xxx_wait indicates success or not:
+ *   true if successful
+ *   false if failed
+ *
+ * Example: Start AES H/W and wait for its finish
+ *   crypto_aes_prestart();
+ *   AES_Start();
+ *   crypto_aes_wait();
+ */
+void crypto_prng_prestart(void);
+bool crypto_prng_wait(void);
+void crypto_aes_prestart(void);
+bool crypto_aes_wait(void);
+
+
 /* Check if buffer can be used for crypto DMA. It has the following requirements:
  * (1) Word-aligned buffer base address
  * (2) Crypto submodule (AES, DES, SHA, etc.) dependent buffer size alignment. Must be 2 power.
diff --git a/targets/TARGET_NUVOTON/TARGET_M480/trng_api.c b/targets/TARGET_NUVOTON/TARGET_M480/trng_api.c
index eeb0a34730..305be2bd21 100644
--- a/targets/TARGET_NUVOTON/TARGET_M480/trng_api.c
+++ b/targets/TARGET_NUVOTON/TARGET_M480/trng_api.c
@@ -36,8 +36,9 @@ static void trng_get(unsigned char *pConversionData)
     p32ConversionData = (uint32_t *)pConversionData;
 
     PRNG_Open(PRNG_KEY_SIZE_256, 1, us_ticker_read());
+    crypto_prng_prestart();
     PRNG_Start();
-    while (!g_PRNG_done);
+    crypto_prng_wait();
 
     PRNG_Read(p32ConversionData);
 }
@@ -85,4 +86,3 @@ int trng_get_bytes(trng_t *obj, uint8_t *output, size_t length, size_t *output_l
 }
 
 #endif
-
diff --git a/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.c b/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.c
index 4c4c52d04f..bc7a58a30c 100644
--- a/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.c
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.c
@@ -24,9 +24,6 @@
 #include "nu_bitutil.h"
 #include "crypto-misc.h"
 
-volatile int g_PRNG_done;
-volatile int g_AES_done;
-
 /* Track if AES H/W is available */
 static uint16_t crypto_aes_avail = 1;
 /* Track if DES H/W is available */
@@ -40,6 +37,14 @@ static uint16_t crypto_init_counter = 0U;
 static bool crypto_submodule_acquire(uint16_t *submodule_avail);
 static void crypto_submodule_release(uint16_t *submodule_avail);
 
+/* Track if PRNG H/W operation is done */
+static volatile uint16_t crypto_prng_done;
+/* Track if AES H/W operation is done */
+static volatile uint16_t crypto_aes_done;
+
+static void crypto_submodule_prestart(volatile uint16_t *submodule_done);
+static bool crypto_submodule_wait(volatile uint16_t *submodule_done);
+
 /* As crypto init counter changes from 0 to 1:
  *
  * 1. Enable crypto clock
@@ -125,6 +130,26 @@ void crypto_sha_release(void)
     crypto_submodule_release(&crypto_sha_avail);
 }
 
+void crypto_prng_prestart(void)
+{
+    crypto_submodule_prestart(&crypto_prng_done);
+}
+
+bool crypto_prng_wait(void)
+{
+    return crypto_submodule_wait(&crypto_prng_done);
+}
+
+void crypto_aes_prestart(void)
+{
+    crypto_submodule_prestart(&crypto_aes_done);
+}
+
+bool crypto_aes_wait(void)
+{
+    return crypto_submodule_wait(&crypto_aes_done);
+}
+
 bool crypto_dma_buff_compat(const void *buff, size_t buff_size, size_t size_aligned_to)
 {
     uint32_t buff_ = (uint32_t) buff;
@@ -146,14 +171,35 @@ static void crypto_submodule_release(uint16_t *submodule_avail)
     while (! core_util_atomic_cas_u16(submodule_avail, &expectedCurrentValue, 1));
 }
 
+static void crypto_submodule_prestart(volatile uint16_t *submodule_done)
+{
+    *submodule_done = 0;
+    
+    /* Ensure memory accesses above are completed before DMA is started
+     *
+     * Replacing __DSB() with __DMB() is also OK in this case.
+     *
+     * Refer to "multi-master systems" section with DMA in:
+     * https://static.docs.arm.com/dai0321/a/DAI0321A_programming_guide_memory_barriers_for_m_profile.pdf
+     */
+    __DSB();
+}
+
+static bool crypto_submodule_wait(volatile uint16_t *submodule_done)
+{
+    while (! *submodule_done);
+    
+    return true;
+}
+
 /* Crypto interrupt handler */
 void CRYPTO_IRQHandler()
 {
     if (PRNG_GET_INT_FLAG()) {
-        g_PRNG_done = 1;
+        crypto_prng_done = 1;
         PRNG_CLR_INT_FLAG();
     }  else if (AES_GET_INT_FLAG()) {
-        g_AES_done = 1;
+        crypto_aes_done = 1;
         AES_CLR_INT_FLAG();
     }
 }
diff --git a/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.h b/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.h
index 4bee4f644c..bec4a96ba5 100644
--- a/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.h
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.h
@@ -23,14 +23,6 @@
 extern "C" {
 #endif
 
-/* Flags to indicate crypto H/W operation has done
- *
- * Crypto driver would clear it before trigger and wait for it. 
- * Crypto interrupt handler would set it on done or error.
- */
-extern volatile int g_PRNG_done;
-extern volatile int g_AES_done;
-
 /* Init/Uninit crypto module */
 void crypto_init(void);
 void crypto_uninit(void);
@@ -54,6 +46,27 @@ void crypto_des_release(void);
 bool crypto_sha_acquire(void);
 void crypto_sha_release(void);
 
+/* Flow control between crypto/xxx start and crypto/xxx ISR 
+ *
+ * crypto_xxx_prestart/crypto_xxx_wait encapsulate control flow between crypto/xxx start and crypto/xxx ISR.
+ * 
+ * crypto_xxx_prestart will also address synchronization issue with memory barrier instruction.
+ *
+ * On finish, return of crypto_xxx_wait indicates success or not:
+ *   true if successful
+ *   false if failed
+ *
+ * Example: Start AES H/W and wait for its finish
+ *   crypto_aes_prestart();
+ *   AES_Start();
+ *   crypto_aes_wait();
+ */
+void crypto_prng_prestart(void);
+bool crypto_prng_wait(void);
+void crypto_aes_prestart(void);
+bool crypto_aes_wait(void);
+
+
 /* Check if buffer can be used for crypto DMA. It has the following requirements:
  * (1) Word-aligned buffer base address
  * (2) Crypto submodule (AES, DES, SHA, etc.) dependent buffer size alignment. Must be 2 power.
diff --git a/targets/TARGET_NUVOTON/TARGET_NUC472/trng_api.c b/targets/TARGET_NUVOTON/TARGET_NUC472/trng_api.c
index b705b7c585..153e1ef42c 100644
--- a/targets/TARGET_NUVOTON/TARGET_NUC472/trng_api.c
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/trng_api.c
@@ -23,7 +23,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include "cmsis.h"
-#include "NUC472_442.h"
 #include "us_ticker_api.h"
 #include "trng_api.h"
 #include "crypto-misc.h"
@@ -41,8 +40,9 @@ static void trng_get(unsigned char *pConversionData)
     p32ConversionData = (uint32_t *)pConversionData;
 
     PRNG_Open(PRNG_KEY_SIZE_256, 1, us_ticker_read());
+    crypto_prng_prestart();
     PRNG_Start();
-    while (!g_PRNG_done);
+    crypto_prng_wait();
 
     PRNG_Read(p32ConversionData);
 }
@@ -88,6 +88,5 @@ int trng_get_bytes(trng_t *obj, uint8_t *output, size_t length, size_t *output_l
     *output_length = cur_length;
     return 0;
 }
- 
-#endif
 
+#endif