lab2-extra: enable LEDs by performing direct register writes

Makefile

@@ -1,10 +1,26 @@
 CROSS_COMPILE = arm-none-eabi-
+GCC_COMPILE_ARGS = -x assembler-with-cpp -c -O0 -g3 -mcpu=cortex-m4 -mthumb -Wall
 
-build: start.S
+build: start.o lab1.o ldscript.ld
-	$(CROSS_COMPILE)gcc -x assembler-with-cpp -c -O0 -g3 -mcpu=cortex-m4 -mthumb -Wall -o start.o start.S
+	$(CROSS_COMPILE)gcc start.o lab1.o \
-	$(CROSS_COMPILE)gcc start.o -mcpu=cortex-m4 -mthumb -Wall --specs=nosys.specs -nostdlib -lgcc -T./ldscript.ld -o start.elf
+		-mcpu=cortex-m4 -mthumb -Wall \
+		--specs=nosys.specs -nostdlib -lgcc -T./ldscript.ld \
+		-o start.elf
 	$(CROSS_COMPILE)objcopy -O binary -F elf32-littlearm start.elf start.bin
 
+start.o: start.S lab1_v2.bin
+	$(CROSS_COMPILE)gcc $(GCC_COMPILE_ARGS) -o start.o start.S
+
+lab1.o: lab1.S
+	$(CROSS_COMPILE)gcc $(GCC_COMPILE_ARGS) -o lab1.o lab1.S
+
+lab1_v2.bin: lab1_v2.S lab1_v2.ld
+	$(CROSS_COMPILE)gcc $(GCC_COMPILE_ARGS) -o lab1_v2.o lab1_v2.S
+	$(CROSS_COMPILE)gcc lab1_v2.o -mcpu=cortex-m4 -mthumb -Wall \
+		--specs=nosys.specs -nostdlib -lgcc -T./lab1_v2.ld \
+		-o lab1_v2.elf
+	$(CROSS_COMPILE)objcopy -O binary lab1_v2.elf lab1_v2.bin
+
 qemu: build
 	qemu-system-gnuarmeclipse --verbose --verbose --board STM32F4-Discovery \
 		--mcu STM32F407VG -d unimp,guest_errors \

lab1.S

@@ -0,0 +1,33 @@
+.syntax unified
+.cpu cortex-m4
+.thumb
+
+.global lab1_v1
+
+#define A 0xED76
+#define B 0xFA53
+#define C 10
+
+lab1_v1:
+    push.n {r0, r1, r2}
+
+    ldr.n r0, =A
+    ldr.n r1, =B
+
+    and r0, r1
+
+    mov r1, #C
+    mov r2, 1
+
+    _fac:
+    mul r2, r2, r1
+    sub r1, #1
+    cmp.n r1, #1
+    bgt _fac
+
+    add r2, r2, r0, lsr #1
+    mov r11, r2
+
+    pop {r0, r1, r2}
+
+    mov pc, lr

lab1_v2.S

@@ -0,0 +1,82 @@
+.syntax unified
+.cpu cortex-m4
+.thumb
+
+.macro BKPT_WRITE addr_src
+    mov r1, \addr_src
+    mov r0, 0x4
+    bkpt 0xAB
+.endm
+
+#define A 0x0321
+#define B 0x7005
+#define C 0x0050
+
+.section .text
+
+lab1_v2:
+    push.n {lr}
+
+    bl calculate_formula_v2
+    bl int_to_str
+
+    pop.n {pc}
+
+calculate_formula_v2:
+    ldr r0, =A
+    ldr r1, =B
+    ldr r2, =C
+
+    cmp r0, r1
+    bgt gret
+    blt less
+
+    same: @ default
+    add r2, r0, r2, lsr #3
+    add r0, r2, r1
+    b finish
+
+    gret:
+    rsb r0, r0, #192
+    sub r0, r0, r1
+    add r0, r2, r0, lsl #2
+    b finish
+
+    less:
+    orr r1, r1, r2
+    mul r0, r0, r1
+
+    finish:
+    mov r10, r0
+    mov pc, lr
+
+int_to_str:
+    mov r3, sp
+
+    @ write newline + NULL terminator
+    mov r5, #0x000A
+    strh r5, [r3, #-2]!
+
+    @ --- handmade modulo ---
+    mov r4, #10
+
+    iterate:
+    mov  r1, r0       @ save orig to r1
+    udiv r0, r0, r4   @ orig/10 and overwrite old orig value
+    mul  r2, r0, r4   @ orig/10*10, place separately
+    subs r5, r1, r2   @ orig - orig/10*10 => modulo (and update flags)
+
+    beq check_if_pending_digits_exist
+    proceed_with_conversion:
+
+    add r5, #48           @ int -> char (only digits, so it's fine)
+    strb r5, [r3, #-1]!   @ write next char to RAM
+    b iterate
+
+    check_if_pending_digits_exist:
+    cmp r0, #0
+    bne proceed_with_conversion
+
+    BKPT_WRITE r3
+
+    mov pc, lr

lab1_v2.ld

@@ -0,0 +1,4 @@
+MEMORY
+{
+    RAM (rwx) : ORIGIN = 0x20000000, LENGTH = 128K
+}

ldscript.ld

@@ -5,3 +5,4 @@ MEMORY
 }
 
 __stack_start = ORIGIN(RAM) + LENGTH(RAM);
+__ram_start = ORIGIN(RAM);

start.S

@@ -2,9 +2,98 @@
 .cpu cortex-m4
 .thumb
 
+.equ SYSTICK_OFFSET, 0xE000E010
+.equ RCC_OFFSET, 0x40023800
+.equ GPIOD_OFFSET, 0x40020C00
+
+.section .text
+
 vtable:
     .word __stack_start
     .word __hard_reset__+1
+    .align 2
+v2_img_start:
+    .incbin "lab1_v2.bin"
+    .align 2
+v2_img_end: @ ==__hard_reset__
 
 __hard_reset__:
-    b __hard_reset__
+    bl setup_leds
+    bl load_systick_timer
+    bl lab1_v1
+
+    bl bootload_v2
+
+    readloop:
+    ldr.n r0, [r7, #8]
+    wfi
+    b.n readloop
+
+load_systick_timer:
+    @ SysTick_LOAD
+    ldr.n r7, =SYSTICK_OFFSET
+    mov r1, #0x1
+    lsl r1, #20
+    str.n r1, [r7, #4]
+
+    @ SysTick_CTRL
+    mov r1, #0x1
+    str.n r1, [r7]
+
+    mov pc, lr
+
+bootload_v2:
+    push {lr}
+
+    @ bootload to ram
+    ldr.n r0, =v2_img_start
+    ldr.n r1, =v2_img_end
+    ldr.n r3, =__ram_start
+
+    copy_loop:
+    ldr r2, [r0], #4
+    str r2, [r3], #4
+    cmp.n r0, r1
+    bne.n copy_loop
+
+    ldr.n r3, =__ram_start
+    add r3, r3, #1
+
+    push {r3}
+    blx r3
+    pop {r3}
+
+    @ patch A
+    ldr r0, =0x707ff64d @ 0xDF7F
+    str r0, [r3, #0xb]
+
+    push {r3}
+    blx r3
+    pop {r3}
+
+    @ patch A and B
+    ldr r0, =0x000af240 @ 0x000A
+    str r0, [r3, #0xb]
+    ldr r0, =0x010af240 @ 0x000A
+    str r0, [r3, #0xf]
+
+    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