diff --git a/flight/PiOS.posix/posix/Libraries/FreeRTOS/Source/portable/GCC/Posix/corvuscorax/thread_signal_test2.c b/flight/PiOS.posix/posix/Libraries/FreeRTOS/Source/portable/GCC/Posix/corvuscorax/thread_signal_test2.c
index 7584e227a..17b9c8cae 100644
--- a/flight/PiOS.posix/posix/Libraries/FreeRTOS/Source/portable/GCC/Posix/corvuscorax/thread_signal_test2.c
+++ b/flight/PiOS.posix/posix/Libraries/FreeRTOS/Source/portable/GCC/Posix/corvuscorax/thread_signal_test2.c
@@ -2,37 +2,84 @@
  * small etst program whether signals between threads work as they should
  */
 
-#include <stdio.h>
+#include <unistd.h>
 #include <time.h>
 #include <pthread.h>
 #include <signal.h>
 
 static pthread_mutex_t Mutex = PTHREAD_MUTEX_INITIALIZER;
-static pthread_mutex_t pfMutex = PTHREAD_MUTEX_INITIALIZER;
 
-#define printf(...) (void)pthread_mutex_lock(&pfMutex);printf(__VA_ARGS__);(void)pthread_mutex_unlock(&pfMutex)
+/**
+ * printf is not thread safe - this little helper function allow debug output in thread safe context
+ */
+/* write a string to a filehandle */
+void print_char(int fh, char *c) {
+	int t=0;
+	while (c[t]!=0) t++;
+	write(fh,c,t);
+}
+
+/* create a dezimal string from an integer */
+int int2char(char* x,long i) {
+	if (i<0) {
+		x[0]='-';
+		return (int2char(&x[1],-i)+1);
+	}
+	if (i==0) {
+		x[0]=0;
+		return 0;
+	}
+	int k=int2char(x,i/10);
+	x[k]='0'+(i%10);
+	return k+1;
+}
+/* print a number*/
+void print_number(int fh, long i) {
+	char buffer[39]; // 39 characters are enough to store a 128 bit integer in dezimal notation (~~3.4* 10^38)
+	char* number=buffer;
+	
+	if (i==0) {
+		number="0";
+	} else {
+		int2char(number,i);
+	}
+	print_char(fh,number);
+}
+
+/**
+ * actual test program
+ */
 
 void sighandler(int sig) {
-	printf("signal handler called in thread %li - signal %i\n",(long)pthread_self(),sig);
+	print_char(2,"signal handler called in thread ");
+	print_number(2,(long)pthread_self());
+	print_char(2," - signal ");
+	print_number(2,sig);
+	print_char(2,"\n");
 }
 
 
 void* threadstart(void* arg) {
 struct timespec timeout;	
 int t;
-	printf("thread %li started\n",(long)pthread_self());
+	print_char(2,"thread ");
+	print_number(2,(long)pthread_self());
+	print_char(2," started \n");
 
 	while (1) {
-		printf("getting mutex\n");
+		print_char(2,"getting mutex\n");
 		pthread_mutex_lock(&Mutex);
-		printf("got mutex\n");
+		print_char(2,"got mutex\n");
 
 
 		for (t=0;t<20;t++) {
 			timeout.tv_sec=1;
 			timeout.tv_nsec=0;
 			nanosleep(&timeout,0);
-			printf("thread %li still running...\n",(long)pthread_self());
+			
+			print_char(2,"thread ");
+			print_number(2,(long)pthread_self());
+			print_char(2," still running...\n");
 		}
 		pthread_mutex_unlock(&Mutex);
 		sleep(1);
@@ -45,25 +92,25 @@ int main(char** argc, int argv) {
 	pthread_t testthread1;	
 	pthread_t testthread2;	
 	struct sigaction action;
-	printf("thread test program\n");
-	printf("installing signal handler\n");
+	print_char(2,"thread test program\n");
+	print_char(2,"installing signal handler\n");
 	action.sa_handler=sighandler;
 	action.sa_flags=0;
 	sigfillset( &action.sa_mask );
 	sigaction(SIGUSR1,&action,NULL);
 
 	sleep(5);
-	printf("starting thread 1\n");
+	print_char(2,"starting thread 1\n");
 	pthread_create(&testthread1,NULL,threadstart,NULL);
 	sleep(5);
-	printf("starting thread 2\n");
+	print_char(2,"starting thread 2\n");
 	pthread_create(&testthread2,NULL,threadstart,NULL);
 	while (1) {
 		sleep(5);
-		printf("sending SIG_USR1 to thread 1\n");
+		print_char(2,"sending SIG_USR1 to thread 1\n");
 		pthread_kill(testthread1,SIGUSR1);
 		sleep(5);
-		printf("sending SIG_USR1 to thread 2\n");
+		print_char(2,"sending SIG_USR1 to thread 2\n");
 		pthread_kill(testthread2,SIGUSR1);
 	}
 }