NeoPixel

Timing

WS2812B Neopixel

• WS2812B data sheet https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf

• 1 bit takes 1.25 us, 24 bit take 30 us
• Timer resolution 0.25 us
• MSB first
• GRB

   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

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

Timer Resolution = 1 / 42 MHz = 23.8 ns

#define T0H		15	// 0.4 us, 0.4 us / 23.8 ns = 16.8
#define T1H		32	// 0.8 us, 33.6
#define T0L		34	// 0.85 us, 35.7
#define T1L		17	// 0.45 us, 18.9
#define TRES  	        420	// 10 us, 420

max. deviation = timer_resolution + 2 cycles = 23.8 ns + 2 * 6 ns = 35.8 ns

WB55

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

Timer Resolution =  1 / 32 MHz = 31.25 ns

#define T0H		11	// 0.4 us, 0.4 us / 31.25 ns = 12.8
#define T1H		24	// 0.8 us, 25.6
#define T0L		26	// 0.85 us, 27.4
#define T1L		13	// 0.45 us, 14.5
#define TRES  	        323	// 10 us, 323

max. deviation = timer_resolution + 2 cycles = 31.25 ns ns + 2 * 31.25 ns = 93.75 ns

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

Timer

TIM6

Set Counter

TIM6->CNT;

Set Time Period

TIM6->ARR; // autoreload

Clear Update Flag

TIM6->SR; // UIF update interrupt flag

Enable/Disable Timer Interrupt

TIM6->DIER; // UIE update interrupt enable

Start/Stop Timer

TIM6->CR1; // UDIS update disable, CEN counter enable