Tomás Vega / PololuLedStrip

Forked PololuLedStrip and modified it to work with the KL25Z. Renamed it to Adafruit_NeoPixel.

Fork of PololuLedStrip by David Grayson

led_strip_write_color.s

Committer:
DavidEGrayson
Date:
2013-03-01
Revision:
5:690fdfb595de
Parent:
4:d3b60bd43811
Child:
6:9d0530b7dae2

File content as of revision 5:690fdfb595de:

    AREA asm_func, CODE, READONLY
    EXPORT led_strip_write_color

led_strip_write_color
    ; 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
    ;   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, r12, r7, lr}
   
    ldr r12, [r0]      ; Read the next color.
    rbit r12, r12      ; Reverse the order of the bits.
    rev r12, r12       ; Reverse the order of the bytes.
    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.
    
    ldr r4, =delay_region_end
    sub r4, r4, #59*2
    blx r4
    
    it cc                ; If the bit to send it 0...
    strcc r3, [r2]       ; Drive the line low.

    ldr r4, =delay_region_end
    sub r4, r4, #59*2
    blx r4

    it cs                ; If the bit to send is 1...
    strcs r3, [r2]       ; Drive the line low.
    
    ldr r4, =delay_region
    add r4, r4, #68
    blx r4
    
    subs r7, r7, #1            ; Decrement the loop counter.
    bne send_led_strip_bit    ; Send another bit if we have not reached zero.
    
led_strip_asm_end
    pop {r4, r12, r7, lr}
    bx lr
    

delay_region
    ; The following is 128 nops.
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
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    nop

    nop
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    nop

    nop
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    nop
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    nop

    nop
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    nop
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    nop
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    nop
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    nop
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    nop
    nop
delay_region_end
    bx lr    ; return
    
    END