lab2-extra: enable LEDs by performing direct register writes

Makefile

@@ -23,7 +23,7 @@ lab1_v2.bin: lab1_v2.S lab1_v2.ld
 
 qemu: build
 	qemu-system-gnuarmeclipse --verbose --verbose --board STM32F4-Discovery \
-		--mcu STM32F407VG -d unimp,guest_errors --nographic \
+		--mcu STM32F407VG -d unimp,guest_errors \
 		--semihosting-config enable=on,target=native -s -S \
 		--image start.bin
 

start.S

@@ -3,6 +3,8 @@
 .thumb
 
 .equ SYSTICK_OFFSET, 0xE000E010
+.equ RCC_OFFSET, 0x40023800
+.equ GPIOD_OFFSET, 0x40020C00
 
 .section .text
 
@@ -16,6 +18,7 @@ v2_img_start:
 v2_img_end: @ ==__hard_reset__
 
 __hard_reset__:
+    bl setup_leds
     bl load_systick_timer
     bl lab1_v1
 
@@ -77,3 +80,20 @@ bootload_v2:
     blx r3
 
     pop {pc}
+
+setup_leds:
+    @ RCC reset & enable GPIOD
+    ldr r0, =RCC_OFFSET
+    mov r1, #0x8
+    str r1, [r0, #0x30] @ ENABLE
+
+    @ GPIOD config
+    ldr r0, =GPIOD_OFFSET
+
+    ldr r1, =0x55000000
+    str r1, [r0] @ Mode Register
+
+    mov r1, #0xF000
+    str r1, [r0, #0x14] @ Output Data Register
+
+    mov pc, lr