Revision 10:f1bb84b97788, committed 2013-03-01

Comitter:

DavidEGrayson

Date:

Fri Mar 01 04:15:35 2013 +0000

Parent:

9:6ffb85d69eaf

Child:

11:e00ba70ac54c

Commit message:

Saved one cycle per bit by shifting the delays to the left in C.

Changed in this revision

--- a/PololuLedStrip.cpp	Fri Mar 01 03:57:49 2013 +0000
+++ b/PololuLedStrip.cpp	Fri Mar 01 04:15:35 2013 +0000
@@ -10,7 +10,7 @@
     int f_mhz = SystemCoreClock / 1000000;
     
     // Arrange for a 700 nanosecond delay between the rise time and the fall time for a 0 bit.
-    led_strip_write_delays[0] = 700*f_mhz/1000 - 25 - 5;
+    led_strip_write_delays[0] = 700*f_mhz/1000 - 32;
     
     // Arrange for a 600 nanosecond delay between the fall time for a 0 bit and the fall time for a 1 bit.
     // This means the pulses representing a 1 will be 700+600 = 1300 nanoseconds.
@@ -19,6 +19,10 @@
     // Arrange for a 1200 nanosecond delay between the fall time for a 1 bit and rise time of the next bit.
     // This means the period of the signal will be 2500 nanoseconds.
     led_strip_write_delays[2] = 1200*f_mhz/1000 - 24;
+    
+    led_strip_write_delays[0] <<= 1;
+    led_strip_write_delays[1] <<= 1;
+    led_strip_write_delays[2] <<= 1;
 }
 
 PololuLedStrip::PololuLedStrip(PinName pinName)

--- a/led_strip_write_color.s	Fri Mar 01 03:57:49 2013 +0000
+++ b/led_strip_write_color.s	Fri Mar 01 04:15:35 2013 +0000
@@ -6,7 +6,6 @@
     delay $id
     ldr r5, =led_strip_write_delays
     ldrb r5, [r5, $id]
-    lsls r5, r5, #1
     ldr r4, =delay_region_end
     subs r4, r4, r5
     blx r4
@@ -30,16 +29,16 @@
     push {r4, r5, r6, r7}
     mov r4, lr
     push {r4}
-    
+
     ldrb r4, [r0, #0]  ; Load red.
     lsls r4, r4, #24
     mov r6, r4         ; Put red in MSB of r6.
     ldrb r4, [r0, #1]  ; Load green.
     lsls r4, r4, #16
-    orrs r6, r6, r4        ; Put green in r6.
+    orrs r6, r6, r4    ; Put green in r6.
     ldrb r4, [r0, #2]  ; Load blue.
     lsls r4, r4, #8
-    orrs r6, r6, r4        ; Put blue in MSB of r6.
+    orrs r6, r6, r4    ; Put blue in MSB of r6.
    
     ; On the Cortex M0 we simply did:
     ;    ldr r6, [r0]       ; Read the color.  Now we have:     xxBbGgRr
@@ -70,7 +69,7 @@
     
     delay #2
     
-    lsls r6, r6, #1           ; Shift color bits.
+    lsls r6, r6, #1              ; Shift color bits.
     subs r7, r7, #1           ; Decrement the loop counter.
     bne send_led_strip_bit    ; Send another bit if we have not reached zero.