leds.c - not perfect but does work

Makefile

+leds.hex: leds.o
+	avr-objcopy -j .text -j .data -O ihex leds.o leds.hex
+
+leds.o:
+	avr-gcc leds.c -o leds.o -Wall -Wextra -Wpedantic -mmcu=atmega328p -Os -std=c99
+
+flash:
+	avrdude -p atmega328p -c gpio -U flash:w:leds.hex

leds.c

@@ -4,13 +4,27 @@
 #include<avr/io.h>
 
 int main(void){
-    DDRD = 0b00111111;
-    DDRB = 0b11111100;
-    PORTD = 0b00000000;
+    DDRD = 0b11111100;
+    DDRB = 0b00111111;
+    PORTD = 0b00000011;
     PORTB = 0b00000000; 
+    char on = 0;
     while(1){
-        if(PORTD != 0b11111111) PORTD = PORTD<<1+1;
-        if(PORTB != 0b11111111) PORTB = PORTB<<1+1;
-        _delay_ms(1000);
+		while(!on){
+			if(PORTD != 0b11111111) PORTD = (PORTD<<1)+1;
+			else{
+				if(PORTB != 0b11111111) PORTB = (PORTB<<1)+1;
+				else on=1;
+			}
+			_delay_ms(250);
+		}
+		while(on){
+			if(PORTB != 0b00000000) PORTB = (PORTB-1)>>1;
+			else{
+				if(PORTD != 0b00000011) PORTD = (PORTD-1)>>1;
+				else on=0;
+			}
+			_delay_ms(250);
+		}
     }
-}
+}
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