NeoPixel

Timing

WS2812B Neopixel

• WS2812B data sheet https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf
• SK6812 https://cdn-shop.adafruit.com/product-files/1138/SK6812+LED+datasheet+.pdf

• 1 bit takes 1.25 us (800 kHz), 24 bit take 30 us
• Timer resolution 0.25 us
• MSB first
• GRB
• 3 cycles for a wait loop

   lsls     r3, r3, #1   // set carry bit
   ittee    cs
   movwcs   r5, #T1H
   movtcs   r5, #T1L   
   movwcc   r5, #T0H
   movtcc   r5, #T0L

HTML Color 0xRRGGBB

F405

https://github.com/spyren/Mecrisp-Cube/blob/F405/Forth/cube/wings.s

Cycle = 1 / 168 MHz = 6 ns
0.4 us / 6 ns = 66.7 -> max. 66 cycles

.equ	T0H,		16	// 0.3 us
.equ	T1H,		40	// 0.8 us
.equ	T0L,		36	// 0.8 us
.equ	T1L,		12	// 0.3 us

WB55

Cycle = 1 / 32 MHz = 31.25 ns
0.4 us / 31.25 ns = 12.8 -> max 12 cycles


.equ	T0H,		4	// 0.4 us / (3 * 31.25 ns) = 4.27  -> 4
.equ	T1H,		8	// 0.8 us / (3 * 31.25 ns) = 8.53  -> 8
.equ	T0L,		5	// 0.85 us / (3 * 31.25 ns) = 9.07 -> 5 (4 turns less)
.equ	T1L,		1	// 0.45 us / (3 * 31.25 ns) = 4.53 -> 1 (4 turns less)

.equ	RESTIME,	533	// 50 us / (3 * 31.25 ns) = 533

//	Registers
.equ	GPIO_BSRR,	0x18	// GPIOx->BSRR bit set/reset


.global		BSP_neopixelDataTx
BSP_neopixelDataTx:
	push	{r4-r6, lr}
	lsl	r2, r2, #8		// r2 = rrggbb00
	mov	r3, r2			// r3 = rrggbb00
	bfc	r3, #16, #16		// r3 = 0000bb00
	rev16	r2, r2			// r2 = ggrr00bb
	bfc	r2, #0, #16		// r2 = ggrr0000
	add	r2, r2, r3		// r2 = ggrrbb00

	lsl	r3, r1, #16		// clear port pin for BSRR
	mov	r6, #24			// 24 bits

	// set DOUT pin low and wait reset time
	str	r3, [r0, #GPIO_BSRR]
	ldr	r4, =RESTIME
1:	subs	r4, r4, #1                                                 1
	bne	1b


                                                                         cycles
bit_loop:
	lsls	r2, r2, #1	// get the next bit -> set the carry bit   1
	ittee	cs                                                         1
	movcs	r4, #T1H                                                   1
	movcs	r5, #T1L                                                   1
	movcc	r4, #T0H                                                   1
	movcc	r5, #T0L                                                   1


	// set DOUT pin high
	str	r1, [r0, #GPIO_BSRR]                                       2
1:	subs	r4, r4, #1                                                 1
	bne	1b                                                         1 (2)

	// set DOUT pin low
	str	r3, [r0, #GPIO_BSRR]                                       2
2:	subs	r5, r5, #1                                                 1
	bne	2b                                                         1 (2)

	subs	r6, r6, #1                                                 1
	bne	bit_loop                                                   2

	pop	{r4-r6, pc}

Set/Reset Portpin

GPIO port bit set/reset register GPIOx_BSRR

• Address offset: 0x18, x = A..K, D8 = PC0
• bit0 .. bit15 bit set
• bit16 .. bit31 bit reset

#define GPIOC_BASE            (AHB1PERIPH_BASE + 0x0800UL)
#define AHB1PERIPH_BASE       (PERIPH_BASE + 0x00020000UL)
#define PERIPH_BASE           0x40000000UL /*!< Peripheral base address in the alias region                                */

GPIOC->BSRR