diff --git a/Makefile b/Makefile
index cc9951e..c8c015f 100644
--- a/Makefile
+++ b/Makefile
@@ -28,12 +28,12 @@ CFLAGS += -MD -MP -MF $(BUILD)/$(*D)/$(*F).d
 CFLAGS += -Wall
 #CFLAGS += -Wextra
 #CFLAGS += -Wcast-align -Wimplicit -Wunused
-#CFLAGS += -Wpointer-arith -Wswitch
-#CFLAGS += -Wredundant-decls -Wreturn-type -Wshadow
-#CFLAGS += -Wbad-function-cast -Wsign-compare -Waggregate-return
+CFLAGS += -Wpointer-arith -Wswitch
+CFLAGS += -Wredundant-decls -Wreturn-type -Wshadow
+CFLAGS += -Wbad-function-cast -Wsign-compare -Waggregate-return
 #CFLAGS += -Wcast-qual -Wnested-externs
-#CFLAGS += -Wmissing-prototypes
-#CFLAGS += -Wstrict-prototypes -Wmissing-declarations
+#CFLAGS += -Wmissing-prototypes -Wmissing-declarations
+CFLAGS += -Wstrict-prototypes 
 
 LDFLAGS = -nostartfiles -t ldscript.ld -Wl,-Map=$@.map,--cref
 LDFLAGS += $(patsubst %,-L%,$(LIBDIRS))
diff --git a/src/at91_tc1.c b/src/at91_tc1.c
index 7ec5f62..99a2870 100644
--- a/src/at91_tc1.c
+++ b/src/at91_tc1.c
@@ -50,19 +50,21 @@ struct channel_data {
 };
 
 static struct channel_data ch_data[MAX_CHANNELS];
-static uint32_t index, count, valid, cal_in_progress;
+static uint32_t count, valid, cal_in_progress;
 
 static void ppm_isr(void)
 {
+	static uint32_t i;
+
 	/* RC Compare -> no TIOA1 edge for 2.5ms */
 	uint32_t status = *AT91C_TC1_SR;
 
 	if (status & AT91C_TC_CPCS) {
 		/* average channel count */
-		count = ((count * 7) + (index << 8)) / 8;
+		count = ((count * 7) + (i << 8)) / 8;
 
 		/* at least 4 channels and a stable channel count */
-		if ((ROUND_DIV256(count) == index) && (index >= 4)) {
+		if ((ROUND_DIV256(count) == i) && (i >= 4)) {
 			if (valid < 10)
 				valid++;
 
@@ -71,7 +73,7 @@ static void ppm_isr(void)
 		}
 
 		/* reset index */
-		index = 0;
+		i = 0;
 	}
 
 	/* edge on TIOA1 */
@@ -81,19 +83,19 @@ static void ppm_isr(void)
 
 		/* valid range: 1 - 2ms */
 		if (width > PULSE_MIN && width < PULSE_MAX) {
-			if (index < ARRAY_SIZE(ch_data)) {
+			if (i < ARRAY_SIZE(ch_data)) {
 				/* calc both filters */
-				ch_data[index].width = ((ch_data[index].width * (PULSE_FILTER_FAST -1)) + width) / PULSE_FILTER_FAST;
-				ch_data[index].width_slow = ((ch_data[index].width_slow * (PULSE_FILTER_SLOW -1)) + width) / PULSE_FILTER_SLOW;
+				ch_data[i].width = ((ch_data[i].width * (PULSE_FILTER_FAST -1)) + width) / PULSE_FILTER_FAST;
+				ch_data[i].width_slow = ((ch_data[i].width_slow * (PULSE_FILTER_SLOW -1)) + width) / PULSE_FILTER_SLOW;
 
 				if (cal_in_progress) {
 					/* use slow filter values, calc center */
-					ch_data[index].min = MIN(ch_data[index].width_slow, ch_data[index].min);
-					ch_data[index].max = MAX(ch_data[index].width_slow, ch_data[index].max);
-					ch_data[index].mid = (ch_data[index].min + ch_data[index].max) / 2;
+					ch_data[i].min = MIN(ch_data[i].width_slow, ch_data[i].min);
+					ch_data[i].max = MAX(ch_data[i].width_slow, ch_data[i].max);
+					ch_data[i].mid = (ch_data[i].min + ch_data[i].max) / 2;
 				}
 			}
-			index++;
+			i++;
 		}
 	}
 }
diff --git a/src/stdio/printf.c b/src/stdio/printf.c
index 13674d6..1e668f0 100644
--- a/src/stdio/printf.c
+++ b/src/stdio/printf.c
@@ -29,13 +29,13 @@ int inline putchar(int c)
 struct snprintf_data {
 	char *bufstart;
 	size_t buflen;
-	int pos;
+	size_t pos;
 };
 
 int snprintf_helper(void *base, const char *buf, size_t len)
 {
 	struct snprintf_data *data = (struct snprintf_data *)base;
-	
+
 	int count = 0;
 	while (len-- && (data->pos < data->buflen))
 		data->bufstart[data->pos++] = *buf++;
@@ -50,7 +50,7 @@ int snprintf(char *buf, size_t len, const char *fmt, ...)
 		.buflen = len,
 		.pos = 0,
 	};
-	
+
 	va_list ap;
 	va_start(ap, fmt);
 	int rc = _putf(snprintf_helper, (void *)&data, fmt, ap);