diff --git a/frameworks/utest/source/default_handlers.cpp b/frameworks/utest/source/default_handlers.cpp
index f8774ebd95..3ec5636f08 100644
--- a/frameworks/utest/source/default_handlers.cpp
+++ b/frameworks/utest/source/default_handlers.cpp
@@ -40,7 +40,7 @@ static void test_failure_handler(const failure_t failure) {
     UTEST_LOG_FUNCTION();
     if (failure.location == LOCATION_TEST_SETUP || failure.location == LOCATION_TEST_TEARDOWN) {
         verbose_test_failure_handler(failure);
-        printf("{{failure}}\n{{end}}\n");
+        utest_printf("{{failure}}\n{{end}}\n");
         while(1) ;
     }
 }
@@ -49,25 +49,25 @@ static void test_failure_handler(const failure_t failure) {
 utest::v1::status_t utest::v1::verbose_test_setup_handler(const size_t number_of_cases)
 {
     UTEST_LOG_FUNCTION();
-    printf(">>> Running %u test cases...\n", number_of_cases);
+    utest_printf(">>> Running %u test cases...\n", number_of_cases);
     return STATUS_CONTINUE;
 }
 
 void utest::v1::verbose_test_teardown_handler(const size_t passed, const size_t failed, const failure_t failure)
 {
     UTEST_LOG_FUNCTION();
-    printf("\n>>> Test cases: %u passed, %u failed", passed, failed);
+    utest_printf("\n>>> Test cases: %u passed, %u failed", passed, failed);
     if (failure.reason == REASON_NONE) {
-        printf("\n");
+        utest_printf("\n");
     } else  {
-        printf(" with reason '%s'\n", stringify(failure.reason));
+        utest_printf(" with reason '%s'\n", stringify(failure.reason));
     }
-    if (failed) printf(">>> TESTS FAILED!\n");
+    if (failed) utest_printf(">>> TESTS FAILED!\n");
 }
 
 void utest::v1::verbose_test_failure_handler(const failure_t failure)
 {
-    printf(">>> failure with reason '%s' during '%s'\n", stringify(failure.reason), stringify(failure.location));
+    utest_printf(">>> failure with reason '%s' during '%s'\n", stringify(failure.reason), stringify(failure.location));
    
 }
 
@@ -75,18 +75,18 @@ void utest::v1::verbose_test_failure_handler(const failure_t failure)
 utest::v1::status_t utest::v1::verbose_case_setup_handler(const Case *const source, const size_t index_of_case)
 {
     UTEST_LOG_FUNCTION();
-    printf("\n>>> Running case #%u: '%s'...\n", index_of_case + 1, source->get_description());
+    utest_printf("\n>>> Running case #%u: '%s'...\n", index_of_case + 1, source->get_description());
     return STATUS_CONTINUE;
 }
 
 utest::v1::status_t utest::v1::verbose_case_teardown_handler(const Case *const source, const size_t passed, const size_t failed, const failure_t failure)
 {
     UTEST_LOG_FUNCTION();
-    printf(">>> '%s': %u passed, %u failed", source->get_description(), passed, failed);
+    utest_printf(">>> '%s': %u passed, %u failed", source->get_description(), passed, failed);
     if (failure.reason == REASON_NONE) {
-        printf("\n");
+        utest_printf("\n");
     } else  {
-        printf(" with reason '%s'\n", stringify(failure.reason));
+        utest_printf(" with reason '%s'\n", stringify(failure.reason));
     }
     return STATUS_CONTINUE;
 }
diff --git a/frameworks/utest/source/greentea_handlers.cpp b/frameworks/utest/source/greentea_handlers.cpp
index 815aa2ac8b..45d544c1de 100644
--- a/frameworks/utest/source/greentea_handlers.cpp
+++ b/frameworks/utest/source/greentea_handlers.cpp
@@ -56,11 +56,11 @@ const handlers_t utest::v1::selftest_handlers = {
 };
 
 
-// --- SPECIAL HANDLERS ---
+// --- SPECIAL HANDLERS ---                     
 static utest::v1::status_t unknown_test_setup_handler(const size_t) {
     UTEST_LOG_FUNCTION();
-    printf(">>> I do not know how to tell greentea that the test started, since\n");
-    printf(">>> you forgot to override the `test_setup_handler` in your specification.\n");
+    utest_printf(">>> I do not know how to tell greentea that the test started, since\n");
+    utest_printf(">>> you forgot to override the `test_setup_handler` in your specification.\n");
 
     return STATUS_ABORT;
 }
diff --git a/frameworks/utest/source/harness.cpp b/frameworks/utest/source/harness.cpp
index b95274fc7e..31c38835f4 100644
--- a/frameworks/utest/source/harness.cpp
+++ b/frameworks/utest/source/harness.cpp
@@ -205,7 +205,6 @@ void Harness::schedule_next_case()
         location = LOCATION_CASE_TEARDOWN;
 
         if (handlers.case_teardown) {
-            // printf("Schedule next case: case_passed = %d, case_failed = %d\n", case_passed, case_failed);    
             utest::v1::status_t status = handlers.case_teardown(case_current, case_passed, case_failed,
                                                      case_failed ? failure_t(REASON_CASES, LOCATION_UNKNOWN) : failure_t(REASON_NONE));
             if (status < STATUS_CONTINUE)          raise_failure(REASON_CASE_TEARDOWN);
@@ -254,10 +253,8 @@ void Harness::validate_callback(const control_t control)
     UTEST_ENTER_CRITICAL_SECTION;
     case_validation_count++;
 
-    // printf("validate_callback: case_validation_count = %d\n", case_validation_count);    
     if (case_timeout_handle != NULL || case_control.timeout == TIMEOUT_FOREVER)
     {
-        // printf("Cancelling scheduled callback\n");        
         scheduler.cancel(case_timeout_handle);
         case_timeout_handle = NULL;
         control_t merged_control = case_control + control;
@@ -272,10 +269,12 @@ bool Harness::is_busy()
 {
     UTEST_LOG_FUNCTION();
     UTEST_ENTER_CRITICAL_SECTION;
-    if (!test_cases)   return false;
-    if (!case_current) return false;
-
-    bool res = (case_current < (test_cases + test_length));
+    bool res = false;
+    
+    if (test_cases && case_current) {    
+        res = (case_current < (test_cases + test_length));
+    }
+    
     UTEST_LEAVE_CRITICAL_SECTION;
     return res;
 }
diff --git a/frameworks/utest/source/shim.cpp b/frameworks/utest/source/shim.cpp
index 8630e0aeb4..656023558c 100644
--- a/frameworks/utest/source/shim.cpp
+++ b/frameworks/utest/source/shim.cpp
@@ -60,6 +60,7 @@ utest_v1_scheduler_t utest_v1_get_scheduler()
 #else
 #   include "mbed.h"
 #endif
+
 // only one callback is active at any given time
 static volatile utest_v1_harness_callback_t minimal_callback;
 static volatile utest_v1_harness_callback_t ticker_callback;
@@ -70,7 +71,6 @@ Timeout utest_timeout_object;
 static void ticker_handler()
 {
     UTEST_LOG_FUNCTION();
-    //printf("\t\t>>> Ticker callback fired for %p.\n", ticker_callback);
     minimal_callback = ticker_callback;
 }
 
@@ -85,7 +85,6 @@ static void *utest_us_ticker_post(const utest_v1_harness_callback_t callback, ti
     UTEST_LOG_FUNCTION();
     timestamp_t delay_us = delay_ms *1000;
     
-    //printf("\t\t>>> Schedule %p with %ums delay => %p.\n", callback, (unsigned int)delay_ms, (void*)1);
     if (delay_ms) {
         ticker_callback = callback;
         // fire the interrupt in 1000us * delay_ms
@@ -96,15 +95,12 @@ static void *utest_us_ticker_post(const utest_v1_harness_callback_t callback, ti
         minimal_callback = callback;
     }
 
-    //printf("Minimal callback = %p, ticker_callback = %p\n", minimal_callback, ticker_callback);
-
     // return a bogus handle
     return (void*)1;
 }
 static int32_t utest_us_ticker_cancel(void *handle)
 {
     UTEST_LOG_FUNCTION();
-    //printf("\t\t>>> Cancel %p => %u\n", handle, (unsigned int)0);
     (void) handle;
     utest_timeout_object.detach();
     return 0;
@@ -117,7 +113,6 @@ static int32_t utest_us_ticker_run()
         // check if a new callback has been set
         if (minimal_callback)
         {
-            //printf("\t\t>>> Firing callback %p\n", minimal_callback);
             // copy the callback
             utest_v1_harness_callback_t callback = minimal_callback;
             // reset the shared callback
@@ -128,6 +123,22 @@ static int32_t utest_us_ticker_run()
     }
     return 0;
 }
+
+int utest_printf(char *str, ...)
+{
+    volatile uint32_t primask = __get_PRIMASK();\
+    if ( (primask & 0x1) == 0){ \
+        va_list vargs;
+    
+        va_start(vargs, str);
+        vprintf(str, vargs);
+        va_end(vargs);
+    }
+
+    return 0;
+}    
+
+
 extern "C" {
 static const utest_v1_scheduler_t utest_v1_scheduler =
 {
diff --git a/frameworks/utest/source/stack_trace.cpp b/frameworks/utest/source/stack_trace.cpp
index 3ff1c874aa..ba0200af03 100644
--- a/frameworks/utest/source/stack_trace.cpp
+++ b/frameworks/utest/source/stack_trace.cpp
@@ -51,15 +51,15 @@ void utest_dump_trace()
 {
     unsigned current = (trace_index == 0) ? UTEST_MAX_BACKTRACE - 1 : trace_index - 1;
 
-    printf("==================================================================\n");
-    printf("Utest back trace: Total calls logged = %u.\n", total_calls);
-    printf("==================================================================\n");
+    utest_printf("==================================================================\n");
+    utest_printf("Utest back trace: Total calls logged = %u.\n", total_calls);
+    utest_printf("==================================================================\n");
     while (current != trace_index) {
     
-        printf("%u > %s\n", current, utest_trace[current].c_str());
+        utest_printf("%u > %s\n", current, utest_trace[current].c_str());
         current = (current == 0) ? UTEST_MAX_BACKTRACE - 1 : current - 1;
     }
-    printf("==================================================================\n");
+    utest_printf("==================================================================\n");
 }
 
 #endif
diff --git a/frameworks/utest/source/unity_handler.cpp b/frameworks/utest/source/unity_handler.cpp
index 827014b391..2b486a5a6b 100644
--- a/frameworks/utest/source/unity_handler.cpp
+++ b/frameworks/utest/source/unity_handler.cpp
@@ -32,3 +32,14 @@ void utest_unity_ignore_failure(void)
     UTEST_LOG_FUNCTION();
     utest::v1::Harness::raise_failure(utest::v1::failure_reason_t(utest::v1::REASON_ASSERTION | utest::v1::REASON_IGNORE));
 }
+
+void utest_safe_putc(int chr)
+{
+    volatile uint32_t primask = __get_PRIMASK();
+    if ( (primask & 0x1) == 0){ 
+        (void)putchar(chr);
+    }
+
+}    
+
+
diff --git a/frameworks/utest/utest/shim.h b/frameworks/utest/utest/shim.h
index f9505d5f73..1e0b0c94c8 100644
--- a/frameworks/utest/utest/shim.h
+++ b/frameworks/utest/utest/shim.h
@@ -76,6 +76,7 @@ extern "C" {
 /// must be implemented by the port
 void utest_v1_enter_critical_section(void);
 void utest_v1_leave_critical_section(void);
+int utest_printf(char *str, ...);
 
 /// This is the default scheduler implementation used by the harness.
 utest_v1_scheduler_t utest_v1_get_scheduler(void);
diff --git a/frameworks/utest/utest/unity_handler.h b/frameworks/utest/utest/unity_handler.h
index 4535785489..5112bcd11f 100644
--- a/frameworks/utest/utest/unity_handler.h
+++ b/frameworks/utest/utest/unity_handler.h
@@ -20,6 +20,8 @@
 #define UTEST_UNITY_ASSERT_FAILURE_H
 
 #include <stdint.h>
+#include <stdio.h>
+#include "cmsis.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -31,6 +33,8 @@ void utest_unity_assert_failure(void);
 /// this function is called from the unity module when an assertion failed, but is ignored.
 void utest_unity_ignore_failure(void);
 
+void utest_safe_putc(int chr);
+
 #ifdef __cplusplus
 }
 #endif