Revision 8:1578776ceac5, committed 2013-03-01

Comitter:

DavidEGrayson

Date:

Fri Mar 01 02:05:21 2013 +0000

Parent:

7:9a088f042ee0

Child:

9:6ffb85d69eaf

Commit message:

Changed the registers so that the push and pop commands can work on the Cortex M0 (LPC 11U24). There are still more things to fix though.

Changed in this revision

--- a/PololuLedStrip.cpp	Fri Mar 01 01:16:48 2013 +0000
+++ b/PololuLedStrip.cpp	Fri Mar 01 02:05:21 2013 +0000
@@ -6,20 +6,30 @@
 
 void PololuLedStrip::calculateDelays()
 {
-    int fmhz = SystemCoreClock / 1000000;
-    led_strip_write_delays[0] = 700*fmhz/1000 - 25;
-    led_strip_write_delays[1] = 600*fmhz/1000 - 19;
-    led_strip_write_delays[2] = 1200*fmhz/1000 - 24;
+    // Get the clock frequency in MHz.
+    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;
+    
+    // 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.
+    led_strip_write_delays[1] = 600*f_mhz/1000 - 19;
+    
+    // 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;
 }
 
 PololuLedStrip::PololuLedStrip(PinName pinName)
 {
     gpio_init(&gpio, pinName, PIN_OUTPUT);
-    calculateDelays();    // Assumption
 }
 
 void PololuLedStrip::write(rgb_color * colors, unsigned int count)
 {
+    calculateDelays();
+
     __disable_irq();   // Disable interrupts temporarily because we don't want our pulse timing to be messed up.
 
     while(count--)

--- a/led_strip_write_color.s	Fri Mar 01 01:16:48 2013 +0000
+++ b/led_strip_write_color.s	Fri Mar 01 02:05:21 2013 +0000
@@ -22,20 +22,20 @@
     ; Additionally, we use these registers:
     ;   R4:  temporary register
     ;   R5:  temporary register
+    ;   R6: shift register that holds the 24-bit color
     ;   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, r5, r12, r7, lr}  ; Push those registers so we can restore them later.
+    push {r4, r5, r6, r7, lr}  ; Push those registers so we can restore them later.
     
-    ldr r12, [r0]      ; Read the color.  Now we have:     xxBbGgRr
-    rbit r12, r12      ; Reverse the order of the bits:    rRgGbBxx
-    rev r12, r12       ; Reverse the order of the bytes:   xxbBgGrR
+    ldr r6, [r0]       ; Read the color.  Now we have:     xxBbGgRr
+    rbit r6, r6        ; Reverse the order of the bits:    rRgGbBxx
+    rev r6, r6         ; Reverse the order of the bytes:   xxbBgGrR
     mov r7, #24        ; Initialize the loop counter register.
     
 send_led_strip_bit
     str r3, [r1]       ; Drive the line high.
-    rrxs r12, r12      ; Rotate right through carry.
+    rrxs r6, r6        ; Rotate right through carry.
     
     delay #0
     
@@ -53,7 +53,7 @@
     bne send_led_strip_bit    ; Send another bit if we have not reached zero.
     
 led_strip_asm_end
-    pop {r4, r5, r12, r7, lr}
+    pop {r4, r5, r6, r7, lr}
     bx lr