Michael Koster
K64F version
Fork of
PololuLedStrip_r8
by 
Michael Koster
Diff: led_strip_write_color_K64F.s
- Revision:
- 25:3b22d6d32a7a
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/led_strip_write_color_K64F.s Thu Dec 11 23:14:12 2014 +0000
@@ -0,0 +1,431 @@
+ AREA asm_func, CODE, READONLY
+ EXPORT led_strip_write_color_K64F
+ IMPORT led_strip_write_delays
+
+ MACRO
+ delay $id
+ ldr r5, =led_strip_write_delays
+ ldrb r5, [r5, $id]
+ ldr r4, =delay_region_end
+ subs r4, r4, r5
+ blx r4
+ MEND
+
+led_strip_write_color_K64F
+ ; 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
+ ; R5: temporary register
+ ; R6: shift register that holds the 24-bit color
+ ; R7: the number of bits we still need to send
+ ; R13: Link Register, holds return addresses.
+
+ ; Push those registers so we can restore them later.
+ push {r4, r5, r6, r7, lr}
+
+ ldrb r6, [r0, #1] ; Load green.
+ lsls r6, r6, #24 ; Put green in MSB of r6.
+ ldrb r4, [r0, #0] ; Load red.
+ lsls r4, r4, #16
+ orrs r6, r6, r4 ; Put red in r6.
+ ldrb r4, [r0, #2] ; Load blue.
+ lsls r4, r4, #8
+ orrs r6, r6, r4 ; Put blue in r6.
+
+ ; On the Cortex-M3 we simply did:
+ ; 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
+ ; and then we used rrxs for shifting to the right through carry.
+
+ ldr r7, =24 ; Initialize the loop counter register.
+
+send_led_strip_bit
+ str r3, [r1] ; Drive the line high.
+
+ ; It doesn't really matter exactly how long we delay here as long as it is
+ ; less than 540 microseconds.
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
+
+ ldr r4, =0x80000000
+ tst r6, r4
+ bne delay0
+ str r3, [r2] ; If the bit to send it 0, drive the line low.
+delay0
+
+ delay #0
+
+ ;tst r6, r8
+ ldr r4, =0x80000000
+ tst r6, r4
+ beq delay1
+ str r3, [r2] ; If the bit to send is 1, drive the line low.
+delay1
+
+ delay #1
+
+ 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.
+ pop {r4, r5, r6, r7, pc} ; Otherwise, restore the registers and return.
+ bx lr;
+
+delay_region
+ ; The following is 128 nops.
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
+ nop
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+
+delay_region_end
+ bx lr ; return
+
+ END
\ No newline at end of file