ws2811.h

/*
 * Copyright 2012 Alan Burlison, alan@bleaklow.com.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * WS2811 RGB LED driver.
 */

#ifndef WS2811_h
#define WS2811_h

// RGB value structure.
typedef struct __attribute__ ((__packed__)) {
    uint8_t r;
    uint8_t g;
    uint8_t b;
} RGB_t;

#ifndef ARRAYLEN
#define ARRAYLEN(A) (sizeof(A) / sizeof(A[0]))
#endif

/*
 * Inline asm macro to output 24-bit RGB value in (G,R,B) order, MSBit first.
 * 0 bits are 250ns hi, 1000ns lo, 1 bits are 1000ns hi, 250ns lo.
 * r18 = red byte to be output
 * r19 = green byte to be output
 * r20 = blue byte to be output
 * r26 = saved SREG
 * r27 = inner loop counter
 */
#define WS2811(PORT, PIN, RGB, LEN) \
asm volatile( \
/* initialise */ \
"    cp %A[len], r1      ; check len > 0, return immediately if it is\n" \
"    cpc %B[len], r1\n" \
"    brne 1f\n" \
"    rjmp 16f\n" \
"1:  ld r18, Z+           ; load in first red byte to be output\n" \
"    ld r19, Z+           ; load in first green byte to be output\n" \
"    ld r20, Z+           ; load in first blue byte to be output\n" \
"    ldi r27, 8           ; load inner loop counter\n" \
"    in r26, __SREG__     ; timing-critical, so no interrupts\n" \
"    cli\n" \
/* green - loop over 8 bits */ \
"2:  sbi  %[port], %[pin] ; pin lo -> hi\n" \
"    sbrc r19, 7          ; test hi bit clear\n" \
"    rjmp 3f              ; true, skip pin hi -> lo\n" \
"    cbi  %[port], %[pin] ; false, pin hi -> lo\n" \
"3:  sbrc r19, 7          ; equalise delay of both code paths\n" \
"    rjmp 4f\n" \
"4:  nop                  ; pulse timing delay\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    lsl r19              ; shift to next bit\n" \
"    dec r27              ; decrement loop counter\n" \
"    cbi %[port], %[pin]  ; pin hi -> lo\n" \
"    brne 2b\n            ; loop if required\n" \
"    ldi r27, 7           ; reload inner loop counter\n" \
/* red - loop over first 7 bits */ \
"5:  sbi %[port], %[pin]  ; pin lo -> hi\n" \
"    sbrc r18, 7          ; test hi bit clear\n" \
"    rjmp 6f              ; true, skip pin hi -> lo\n" \
"    cbi %[port], %[pin]  ; false, pin hi -> lo\n" \
"6:  sbrc r18, 7          ; equalise delay of both code paths\n" \
"    rjmp 7f\n" \
"7:  nop                  ; pulse timing delay\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    lsl r18              ; shift to next bit\n" \
"    dec r27              ; decrement inner loop counter\n" \
"    cbi %[port], %[pin]  ; pin hi -> lo\n" \
"    brne 5b              ; inner loop, if required\n" \
"    nop                  ; equalise delay of both code paths\n" \
/* red, 8th bit - output & fetch next values */ \
"    sbi %[port], %[pin]  ; pin lo -> hi\n" \
"    sbrc r18, 7          ; test hi bit clear\n" \
"    rjmp 8f              ; true, skip pin hi -> lo\n" \
"    cbi %[port], %[pin]  ; false, pin hi -> lo\n" \
"8:  sbrc r18, 7          ; equalise delay of both code paths\n" \
"    rjmp 9f\n" \
"9:  nop                  ; pulse timing delay\n" \
"    nop\n" \
"    nop\n" \
"    ld r18, Z+           ; load next red byte\n" \
"    ld r19, Z+           ; load next green byte\n" \
"    ldi r27, 7           ; reload inner loop counter\n" \
"    cbi %[port], %[pin]  ; pin hi -> lo\n" \
"    nop                  ; pulse timing delay\n" \
"    nop\n" \
/* blue - loop over first 7 bits */ \
"10:  sbi %[port], %[pin] ; pin lo -> hi\n" \
"    sbrc r20, 7          ; test hi bit clear\n" \
"    rjmp 11f             ; true, skip pin hi -> lo\n" \
"    cbi %[port], %[pin]  ; false, pin hi -> lo\n" \
"11: sbrc r20, 7          ; equalise delay of both code paths\n" \
"    rjmp 12f\n" \
"12: nop                  ; pulse timing delay\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    nop\n" \
"    lsl r20              ; shift to next bit\n" \
"    dec r27              ; decrement inner loop counter\n" \
"    cbi %[port], %[pin]  ; pin hi -> lo\n" \
"    brne 10b             ; inner loop, if required\n" \
"    nop                  ; equalise delay of both code paths\n" \
/* blue, 8th bit -  output & handle outer loop */ \
"    sbi %[port], %[pin]  ; pin lo -> hi\n" \
"    sbrc r20, 7          ; test hi bit clear\n" \
"    rjmp 13f             ; true, skip pin hi -> lo\n" \
"    cbi %[port], %[pin]  ; false, pin hi -> lo\n" \
"13: sbrc r20, 7          ; equalise delay of both code paths\n" \
"    rjmp 14f\n" \
"14: nop                  ; pulse timing delay\n" \
"    nop\n" \
"    ldi r27, 8           ; reload inner loop counter\n" \
"    sbiw %A[len], 1      ; decrement outer loop counter\n" \
"    breq 15f             ; exit outer loop if zero\n" \
"    ld r20, Z+           ; load in next blue byte\n" \
"    cbi %[port], %[pin]  ; pin hi -> lo\n" \
"    rjmp 2b              ; outer loop, if required\n" \
"15: nop                  ; pulse timing delay\n" \
"    cbi %[port], %[pin]  ; pin hi -> lo\n" \
"    nop                  ; pulse timing delay\n" \
"    nop\n" \
"    out __SREG__, r26    ; reenable interrupts\n" \
"16:\n" \
: \
: [rgb] "z" (RGB), \
  [len] "w" (LEN), \
  [port] "I" (_SFR_IO_ADDR(PORT)), \
  [pin] "I" (PIN) \
: "r18", "r19", "r20", "r26", "r27", "cc", "memory" \
)

/*
 * Define a C function to wrap the inline WS2811 macro for a given port and pin.
 */
#define DEFINE_WS2811_FN(NAME, PORT, PIN) \
extern void NAME(const RGB_t *rgb, uint16_t len) __attribute__((noinline)); \
void NAME(const RGB_t *rgb, uint16_t len) { WS2811(PORT, PIN, rgb, len); }

#endif /* WS2811_h */