working demo

lab3subroutines/src/main.s

@@ -12,4 +12,136 @@
 .global main
 
 main:
+	mov r0, #0
+	mov r1, #0
+	mov r2, #0
 
+main_loop:
+
+    mov r0, #1234
+    bl num_to_ASCII
+    mov r1, r0
+    # r1 is 4 character ASCII value
+    mov r0, #500
+    # Display 1
+   	ubfx r0, r1, #24, #8
+    bl num_to_LED
+    mov r0, #500
+    bl delay_ms
+    # Display 2
+    ubfx r0, r1, #16, #8
+    bl num_to_LED
+    mov r0, #500
+    bl delay_ms
+    # Display 3
+    ubfx r0, r1, #8, #8
+    bl num_to_LED
+    mov r0, #500
+    bl delay_ms
+    # Display 4
+    ubfx r0, r1, #0, #8
+    bl num_to_LED
+    mov r0, #500 
+    bl delay_ms
+    b main_loop
+
+
+end:
+    b end
+.global num_to_ASCII
+
+# Takes in a value from 0-9999 and converts it to ASCII
+# Input:
+#       r0: Input binary value
+# Output:
+#       r1: Output 4 ASCII characters
+num_to_ASCII:
+
+    # If outside of range, return ASCII "Err."
+    push {r1,r2,r3,lr}
+
+    cmp r0,#0
+    blt out_of_range
+    @ cmp r0,#9999
+    @ bgt out_of_range
+
+    # Normal conversion behavior
+    mov r1, #16
+    lsl r0, #3
+    sub r1, #3
+shift_cycle:
+
+    lsl r0, #1
+    sub r1, #1
+
+# Verify Each Nibble is less than or equal to 4
+    ubfx r2, r0, #16, #4
+    # If value is less than or equal to 4, then skip to next nibble
+    cmp r2, #4
+    ble 2f
+    add r2, #3
+    bfi r0, r2, #16, #4
+2:  ubfx r2, r0, #20, #4
+    # If value is less than or equal to 4, then skip to next nibble
+    cmp r2, #4
+    ble 3f
+    add r2, #3
+    bfi r0, r2, #20, #4
+3:  ubfx r2, r0, #24, #4
+    # If value is less than or equal to 4, then skip to next nibble
+    cmp r2, #4
+    ble 4f
+    add r2, #3
+    bfi r0, r2, #24, #4
+4:  ubfx r2, r0, #28, #4
+    # If value is less than or equal to 4 skip to end
+    cmp r2, #4
+    ble end_verify_nibbles
+    add r2, #3
+    bfi r0, r2, #28, #4
+end_verify_nibbles:
+
+    # If value hasn't been shifted 16 times, shift again
+    cmp r1, #0
+    bne shift_cycle
+    mov r3, #3
+# Encode BCD numbers to ASCII
+
+    # Extract ones nibble
+    ubfx r2, r0, #16, #4
+    # Insert ones nibble
+    bfi r1, r2, #0, #4
+    # Insert 3 in front of nibble for ASCII encoding
+    bfi r1, r3, #4, #4
+
+    # Extract tens nibble
+    ubfx r2, r0, #20, #4
+    # Insert tens nibble
+    bfi r1, r2, #8, #4
+    # Insert 3 in front of nibble for ASCII encoding
+    bfi r1, r3, #12, #4
+
+    # Extract hundreds nibble
+    ubfx r2, r0, #24, #4
+    # Insert hundreds nibble
+    bfi r1, r2, #16, #4
+    # Insert 3 in front of nibble for ASCII encoding
+    bfi r1, r3, #20, #4
+
+    # Extract thousands nibble
+    ubfx r2, r0, #28, #4
+    # Insert thousands nibble
+    bfi r1, r2, #24, #4
+    # Insert 3 in front of nibble for ASCII encoding
+    bfi r1, r3, #28, #4
+
+    b end_ASCII
+out_of_range:
+    # Insert ASCII "Err."
+    movw r1, #0x722E
+    movt r1, #0x4572
+
+end_ASCII:
+	mov r0, r1
+    pop {r1,r2,r3,lr}
+    bx lr