Added compile flag to replace TF with simple loopback for transport testing

gex.mk

@@ -115,5 +115,9 @@ GEX_SRC_DIR += \
 endif
 
 ifeq '$(DISABLE_TEST_UNIT)' '1'
-GEX_CDEFS += -DDISABLE_TEST_UNIT
+GEX_CDEFS += -DDISABLE_TEST_UNIT=1
+endif
+
+ifeq '$(CDC_LOOPBACK_TEST)' '1'
+GEX_CDEFS += -DCDC_LOOPBACK_TEST=1
 endif

tasks/task_msg.c

@@ -83,7 +83,12 @@ void TaskMsgJob(const void *argument)
         }
         else {
             assert_param(slot.msg.len > 0 && slot.msg.len <= MSG_QUE_SLOT_SIZE); // check the len is within bounds
+
+            #if CDC_LOOPBACK_TEST
+                TF_WriteImpl(comm, slot.msg.data, slot.msg.len);
+            #else
                 TF_Accept(comm, slot.msg.data, slot.msg.len);
+            #endif
         }
 
         #if USE_STACK_MONITOR