Revision 4:d3b60bd43811, committed 2013-02-28

Comitter:

DavidEGrayson

Date:

Thu Feb 28 00:42:44 2013 +0000

Parent:

3:809dae64a994

Child:

5:690fdfb595de

Commit message:

Proof of the concept that we can achieve variable delays by jumping into a particular portion of a large subroutine with noops.

Changed in this revision

--- a/PololuLedStrip.cpp	Wed Feb 27 02:45:31 2013 +0000
+++ b/PololuLedStrip.cpp	Thu Feb 28 00:42:44 2013 +0000
@@ -2,6 +2,9 @@
 
 bool PololuLedStrip::interruptFriendly = false;
 
+// TODO: read clock frequency from SystemCoreClock and use that to make this work on different boards.
+// calculate the three delays needed and pass them to the assembly.  The assembly can implement them with computed jumps.
+
 PololuLedStrip::PololuLedStrip(PinName pinName)
 {
     gpio_init(&gpio, pinName, PIN_OUTPUT);

--- a/led_strip_write_color.s	Wed Feb 27 02:45:31 2013 +0000
+++ b/led_strip_write_color.s	Thu Feb 28 00:42:44 2013 +0000
@@ -2,7 +2,7 @@
     EXPORT led_strip_write_color
 
 led_strip_write_color
-    push    {r12, r7}
+    push    {r4, r12, r7}
    
     ldr r12, [r0]      ; Read the next color.
     rbit r12, r12      ; Reverse the order of the bits.
@@ -156,9 +156,21 @@
     it cs                ; If the bit to send is 1...
     strcs r3, [r2]       ; Drive the line low.
     
-    nop
-    nop
-    nop
+    ldr r4, =delay_region
+    add r4, r4, 34*2
+    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.
+    
+led_strip_asm_end
+    pop {r4, r12, r7}
+    bx lr
+    
+
+delay_region
+    ; The following is 128 no-ops
     nop
     nop
     nop
@@ -166,18 +178,16 @@
     nop
     nop
     nop
-    
-    nop
-    nop
-    nop
-    nop
     nop
     nop
     nop
     nop
     nop
     nop
-    
+    nop
+    nop
+    nop
+
     nop
     nop
     nop
@@ -188,18 +198,19 @@
     nop
     nop
     nop
-    
     nop
     nop
     nop
     nop
     nop
     nop
+
     nop
     nop
     nop
     nop
-    
+    nop
+    nop
     nop
     nop
     nop
@@ -221,6 +232,12 @@
     nop
     nop
     nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
 
     nop
     nop
@@ -232,6 +249,12 @@
     nop
     nop
     nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
 
     nop
     nop
@@ -243,17 +266,12 @@
     nop
     nop
     nop
-
     nop
     nop
     nop
     nop
     nop
     nop
-    nop
-    nop
-    nop
-    nop   
 
     nop
     nop
@@ -265,21 +283,29 @@
     nop
     nop
     nop
-    
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+
     nop
     nop
     nop
     nop
     nop
     nop
-    nop   
-    
-    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.
-    
-led_strip_asm_end
-    pop {r12, r7}
-    bx lr
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    bx lr    ; return
     
     END
\ No newline at end of file