Diff: led_strip_write_color.s

Revision:

5:690fdfb595de

Parent:

4:d3b60bd43811

Child:

6:9d0530b7dae2

--- a/led_strip_write_color.s	Thu Feb 28 00:42:44 2013 +0000
+++ b/led_strip_write_color.s	Fri Mar 01 00:05:26 2013 +0000
@@ -2,7 +2,20 @@
     EXPORT led_strip_write_color
 
 led_strip_write_color
-    push    {r4, r12, r7}
+    ; Register usage:
+    ; These are the first 4 arguments to the method:
+    ;   R0:  pointer to the color to send
+    ;   R1:  pointer to the register for setting the pin
+    ;   R2:  pointer to the register for clearing the pin
+    ;   R3:  pin mask
+    ; Additionally, we use these registers:
+    ;   R4:  temporary register
+    ;   R7:  the number of bits we still need to send
+    ;   R12: shift register that holds the 24-bit color
+    ;   R13: Link Register, holds return addresses.
+    
+    
+    push    {r4, r12, r7, lr}
    
     ldr r12, [r0]      ; Read the next color.
     rbit r12, r12      ; Reverse the order of the bits.
@@ -13,164 +26,34 @@
     str r3, [r1]       ; Drive the line high.
     rrxs r12, r12      ; Rotate right through carry.
     
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-        
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-        
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-        
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-        
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    
-    nop
-    nop
-    nop
-    nop
+    ldr r4, =delay_region_end
+    sub r4, r4, #59*2
+    blx r4
     
     it cc                ; If the bit to send it 0...
     strcc r3, [r2]       ; Drive the line low.
 
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-
+    ldr r4, =delay_region_end
+    sub r4, r4, #59*2
+    blx r4
 
     it cs                ; If the bit to send is 1...
     strcs r3, [r2]       ; Drive the line low.
     
     ldr r4, =delay_region
-    add r4, r4, 34*2
+    add r4, r4, #68
     blx r4
     
-    sub r7, r7, #1               ; Decrement the loop counter.
-    cbz r7, led_strip_asm_end    ; If we have sent 24 bits, go to the end.
-    b send_led_strip_bit         ; Otherwise, go back and send another bit.
+    subs r7, r7, #1            ; Decrement the loop counter.
+    bne send_led_strip_bit    ; Send another bit if we have not reached zero.
     
 led_strip_asm_end
-    pop {r4, r12, r7}
+    pop {r4, r12, r7, lr}
     bx lr
     
 
 delay_region
-    ; The following is 128 no-ops
+    ; The following is 128 nops.
     nop
     nop
     nop
@@ -306,6 +189,7 @@
     nop
     nop
     nop
+delay_region_end
     bx lr    ; return
     
     END
\ No newline at end of file