pxt-calliope/libs/neopixel/sendbuffer.asm

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NASM
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sendBufferAsm:
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push {r4,r5,r6,r7,lr}
mov r4, r0 ; save buff
mov r6, r1 ; save pin
mov r0, r4
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bl BufferMethods::length
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mov r5, r0
mov r0, r4
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bl BufferMethods::getBytes
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mov r4, r0
; setup pin as digital
mov r0, r6
movs r1, #0
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bl pins::digitalWritePin
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; load pin address
mov r0, r6
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bl pins::getPinAddress
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ldr r0, [r0, #8] ; get mbed DigitalOut from MicroBitPin
ldr r1, [r0, #4] ; r1-mask for this pin
ldr r2, [r0, #16] ; r2-clraddr
ldr r3, [r0, #12] ; r3-setaddr
cpsid i ; disable irq
b .start
.nextbit: ; C0
str r1, [r3, #0] ; pin := hi C2
tst r6, r0 ; C3
bne .islate ; C4
str r1, [r2, #0] ; pin := lo C6
.islate:
lsrs r6, r6, #1 ; r6 >>= 1 C7
bne .justbit ; C8
; not just a bit - need new byte
adds r4, #1 ; r4++ C9
subs r5, #1 ; r5-- C10
bcc .stop ; if (r5<0) goto .stop C11
.start:
movs r6, #0x80 ; reset mask C12
nop ; C13
.common: ; C13
str r1, [r2, #0] ; pin := lo C15
; always re-load byte - it just fits with the cycles better this way
ldrb r0, [r4, #0] ; r0 := *r4 C17
b .nextbit ; C20
.justbit: ; C10
; no nops, branch taken is already 3 cycles
b .common ; C13
.stop:
str r1, [r2, #0] ; pin := lo
cpsie i ; enable irq
pop {r4,r5,r6,r7,pc}
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