File content as of revision 4:623b0c643dd6:

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; NeoCore.s
; 
; Allen Wild
; March 2014
;
; ARM assembly functions for writing to Adafruit NeoPixels
; with the mbed NXP LPC1768
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	AREA neo_core, CODE, READONLY
	
	IMPORT neo_fio_reg
	IMPORT neo_bitmask
	
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neo_write_pin
; Set the GPIO pin to the value passed in R0
; Registers and bitmasks are stored in variables set by the C++ library
	LDR		R1, =neo_fio_reg	; load pointers to register values
	LDR		R2, =neo_bitmask
	LDR		R1, [R1]			; load actual values from memory
	LDR		R2, [R2]

	CMP		R0, #0			; VALUE == 0 ?
	ITE EQ					; (IF-THEN-ELSE) ON NEXT TWO INSTRUCTIONS USING "EQ" FLAG
	STREQ	R2, [R1,#0x1C]	; if==0, CLEAR BIT
	STRNE	R2, [R1,#0x18]	; if==1, SET BIT
	BX		LR

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neo_zero
; Output a NeoPixel zero, composed of a short
; HIGH pulse and a long LOW pulse
	PUSH	{LR}
	MOV		R0, #1
	BL		neo_write_pin	; set pin high
	
	MOV		R0, #10			; delay for long enough
	BL		neo_delay
	
	MOV		R0, #0			; set pin low
	BL		neo_write_pin
	
	MOV		R0, #20			; delay
	BL		neo_delay
	
	POP		{LR}
	BX		LR

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neo_one
; Output a NeoPixel one, composed of a long
; HIGH pulse and a short LOW pulse
	PUSH	{LR}
	MOV		R0, #1
	BL		neo_write_pin
	
	MOV		R0, #86
	BL		neo_delay
	
	MOV		R0, #0
	BL		neo_write_pin
	
	NOP		; really short delay
	NOP
	NOP
	
	POP		{LR}
	BX		LR
	
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	EXPORT neo_out ; void neo_out(int *data, int n);
; Main function called from the C++ library
; R0 contains a pointer to the array of color data to send
; R1 contains the number of bytes of data to send
neo_out
	PUSH	{LR, R4, R5, R6, R7, R8}
	MOV		R7, R1		; move length to R7
	MOV		R6, R0		; move address to R6
	
neo_byteloop
	LDRB	R5, [R6]	; load byte to send
	MOV		R4, #0x80	; load initial bitmask
	
neo_bitloop
	AND		R3, R5, R4	; mask current byte
	CMP		R3, #0
	BLEQ	neo_zero	; send current bit
	BLNE	neo_one
	
	LSR		R4, R4, #1	; shift bitmask right one
	CMP		R4, #0		; if still more bits, loop back
	BNE		neo_bitloop
	
	ADD		R6, R6, #1	; increment address
	SUB		R7, R7, #1	; decrement count
	CMP		R7, #0
	BNE		neo_byteloop	; continue if not done

	MOV		R0, #0
	BL		neo_write_pin
	POP		{R8, R7, R6, R5, R4, LR}
	BX		LR

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neo_delay
; delay the specified number of cycles in R0 with a bunch of nops
	LDR		R2, =neo_delay_end
	SUB		R2, R2, R0
	BX		R2
	NOP
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neo_delay_end
	BX	 LR

	END ; end code region