diff --git a/cpu.cpp b/cpu.cpp
index 2bb4254..f2067ff 100644
--- a/cpu.cpp
+++ b/cpu.cpp
@@ -1664,8 +1664,10 @@ void cpu::trap(uint16_t vector, const int new_ipl, const bool is_interrupt)
 {
 	DOLOG(debug, true, "*** CPU::TRAP %o, new-ipl: %d, is-interrupt: %d ***", vector, new_ipl, is_interrupt);
 
-	uint16_t before_psw            = 0;
-	uint16_t before_pc             = 0;
+	uint16_t before_psw = 0;
+	uint16_t before_pc  = 0;
+
+	it_is_a_trap = true;
 
 	for(;;) {
 		try {
@@ -1688,11 +1690,9 @@ void cpu::trap(uint16_t vector, const int new_ipl, const bool is_interrupt)
 			}
 			else {
 				before_psw = getPSW();
-
 				b->addToMMR1(-2, 6);
 
 				before_pc  = getPC();
-
 				b->addToMMR1(-2, 6);
 
 				// TODO set MMR2?
@@ -2224,6 +2224,8 @@ std::map<std::string, std::vector<std::string> > cpu::disassemble(const uint16_t
 
 void cpu::step_a()
 {
+	it_is_a_trap = false;
+
 	if ((b->getMMR0() & 0160000) == 0)
 		b->clearMMR1();
 
diff --git a/cpu.h b/cpu.h
index 48ff371..e064dcd 100644
--- a/cpu.h
+++ b/cpu.h
@@ -36,10 +36,10 @@ private:
 	uint16_t fpsr  { 0 };
 	uint16_t stackLimitRegister { 0377 };
 	int      processing_trap_depth { 0 };
-	uint64_t instruction_count { 0 };
-	uint64_t running_since     { 0 };
-
-	uint64_t mtpi_count { 0 };
+	uint64_t instruction_count { 0     };
+	uint64_t running_since     { 0     };
+	bool     it_is_a_trap      { false };
+	uint64_t mtpi_count        { 0     };
 
 	// level, vector
 	std::map<uint8_t, std::set<uint8_t> > queued_interrupts;
@@ -114,6 +114,7 @@ public:
 	void queue_interrupt(const uint8_t level, const uint8_t vector);
 
 	void trap(uint16_t vector, const int new_ipl = -1, const bool is_interrupt = false);
+	bool is_it_a_trap() const { return it_is_a_trap; }
 
 	bool getPSW_c() const;
 	bool getPSW_v() const;
diff --git a/json/produce-json.py b/json/produce-json.py
index 2606614..d0d8eb3 100755
--- a/json/produce-json.py
+++ b/json/produce-json.py
@@ -74,7 +74,11 @@ class test_generator:
 
         # TODO what is the maximum size of an instruction?
         mem_kv = []
-        mem_kv.append((addr + 0, random.randint(0, 65536 - 8)))
+        while True:
+            instr = random.randint(0, 65536 - 8)
+            if instr != 1:  # TODO ignore 'WAIT' instruction
+                break
+        mem_kv.append((addr + 0, instr))
         mem_kv.append((addr + 2, random.randint(0, 65536 - 8)))
         mem_kv.append((addr + 4, random.randint(0, 65536 - 8)))
         mem_kv.append((addr + 6, random.randint(0, 65536 - 8)))
@@ -142,7 +146,8 @@ fh = open(sys.argv[1], 'w')
 t = test_generator()
 
 tests = []
-for i in range(0, 4096):
+for i in range(0, 131072):
+    print(f'{i}\r', end='')
     test = t.create_test()
     if test != None:
         tests.append(test)
diff --git a/main.cpp b/main.cpp
index cc7a51e..c198af7 100644
--- a/main.cpp
+++ b/main.cpp
@@ -69,6 +69,8 @@ int run_cpu_validation(const std::string & filename)
 		cpu *c = new cpu(b, &event);
 		b->add_cpu(c);
 
+		uint16_t start_pc = 0;
+
 		{
 			// initialize
 			json_t *memory_before = json_object_get(test, "memory-before");
@@ -101,7 +103,8 @@ int run_cpu_validation(const std::string & filename)
 		{
 			json_t *b_pc = json_object_get(registers_before, "pc");
 			assert(b_pc);
-			c->setPC(json_integer_value(b_pc));
+			start_pc = json_integer_value(b_pc);
+			c->setPC(start_pc);
 		}
 
 		// TODO SP[]
@@ -173,6 +176,13 @@ int run_cpu_validation(const std::string & filename)
 			}
 
 			if (err) {
+				if (c->is_it_a_trap())
+					DOLOG(warning, true, "Error by TRAP");
+				else {
+					auto data = c->disassemble(start_pc);
+					DOLOG(warning, true, "Error by instruction %s", data["instruction-text"].at(0).c_str());
+				}
+
 				char *js = json_dumps(test, 0);
 				DOLOG(warning, true, "%s\n", js);  // also emit empty line(!)
 				free(js);