WS2812灯珠（三）-- STM32 PWM+DMA方式驱动
一、理论
PWM输出就是对外输出脉宽（即占空比）可调的方波信号，信号频率由自动重装载寄存器ARR的值决定，占空比由比较寄存器CCR的值决定。
由WS2812规格书可知：
-
WS2812灯珠的通信速度为800Kbit/s。
-
数据传输时间（TH+TL=1.25us+/-600ns）
T0H 0码，高电平时间 0.35us +/-150ns T1H 1码，高电平时间 0.7us +/-150ns T0L 0码，低电平时间 0.8us +/-150ns T1L 1码，低电平时间 0.6us +/-150ns RES 帧单位，低电平时间 50us以上
故在配置STM32定时器时可设置，预分频因子为0，自动重装载初值为90-1，则频率为72M/90 = 800K。
设值占空比为45可满足1码的时间要求，设值占空比为30可满足0码的时间要求。
二、代码实践
- 这里在代码中具体用到的时PA0引脚（TIM2的CH1）
头文件：通过宏配置需要控制的灯珠数目
#ifndef __BSP_WS281X_H
#define __BSP_WS281X_H
#include "stm32f10x.h"
#define PIXEL_NUM 16
#define GRB 24 //3*8
#define WS_HIGH 45
#define WS_LOW 30
void WS281x_Init(void);
void WS281x_CloseAll(void);
uint32_t WS281x_Color(uint8_t red, uint8_t green, uint8_t blue);
void WS281x_SetPixelColor(uint16_t n, uint32_t GRBColor);
void WS281x_SetPixelRGB(uint16_t n ,uint8_t red, uint8_t green, uint8_t blue);
void WS281x_Show(void);
void WS281x_RainbowCycle(uint8_t wait);
void WS281x_TheaterChase(uint32_t c, uint8_t wait);
void WS281x_ColorWipe(uint32_t c, uint8_t wait);
void WS281x_Rainbow(uint8_t wait);
void WS281x_TheaterChaseRainbow(uint8_t wait);
#endif /* __BSP_WS281X_H */源文件：
#include "bsp_ws281x.h"
#include "bsp_systick.h"
uint16_t pixelBuffer[PIXEL_NUM][GRB];
void WS281x_Init(void)
{
GPIO_InitTypeDef GPIO_InitStruct;
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;
TIM_OCInitTypeDef TIM_OCInitStruct;
DMA_InitTypeDef DMA_InitStructure;
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1,ENABLE);
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_0;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStruct);
TIM_TimeBaseInitStruct.TIM_Prescaler = 0;
TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInitStruct.TIM_Period = 90 - 1; //72M / 90 = 800K
TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitStruct);
TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStruct.TIM_Pulse = 0;
TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OCInitStruct.TIM_OCIdleState = TIM_OCIdleState_Reset;
TIM_OC1Init(TIM2, &TIM_OCInitStruct);
TIM_CtrlPWMOutputs(TIM2,ENABLE); //MOE 主输出使能
/*必须有下面该语句，否则时序会错乱*/
TIM_OC1PreloadConfig(TIM2, TIM_OCPreload_Enable); //CH1预装载使能
TIM_Cmd(TIM2, DISABLE);
TIM_DMACmd(TIM2, TIM_DMA_CC1, ENABLE);
DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&(TIM2->CCR1);
DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)pixelBuffer;
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
DMA_InitStructure.DMA_BufferSize = PIXEL_NUM * GRB;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;
DMA_InitStructure.DMA_Priority = DMA_Priority_Medium;
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
DMA_Init(DMA1_Channel5, &DMA_InitStructure);
DMA_Cmd(DMA1_Channel5, DISABLE);
/*关闭所有灯珠*/
WS281x_CloseAll();
delay_ms(100);
}
void WS281x_CloseAll(void)
{
uint16_t i;
uint8_t j;
for(i = 0; i < PIXEL_NUM; ++i)
{
for(j = 0; j < 24; ++j)
{
pixelBuffer[i][j] = WS_LOW;
}
}
WS281x_Show();
}
uint32_t WS281x_Color(uint8_t red, uint8_t green, uint8_t blue)
{
return green << 16 | red << 8 | blue;
}
void WS281x_SetPixelColor(uint16_t n, uint32_t GRBColor)
{
uint8_t i;
if(n < PIXEL_NUM)
{
for(i = 0; i < GRB; i++)
{
pixelBuffer[n][i] = ((GRBColor << i) & 0x800000) ? WS_HIGH : WS_LOW;
}
}
}
void WS281x_SetPixelRGB(uint16_t n ,uint8_t red, uint8_t green, uint8_t blue)
{
uint8_t i;
if(n < PIXEL_NUM)
{
for(i = 0; i < GRB; ++i)
{
pixelBuffer[n][i] = (((WS281x_Color(red,green,blue) << i) & 0X800000) ? WS_HIGH : WS_LOW);
}
}
}
//下面函数中语句执行的顺序相当关键，不能错。
//从示波器看，非当前的执行顺序，最后一个灯的波形序列会多。
void WS281x_Show(void)
{
DMA_SetCurrDataCounter(DMA1_Channel5, PIXEL_NUM * GRB);
TIM_Cmd(TIM2, ENABLE);
DMA_Cmd(DMA1_Channel5, ENABLE);
while(DMA_GetFlagStatus(DMA1_FLAG_TC5) != SET);
TIM_Cmd(TIM2, DISABLE);
//TIM_SetCompare1(TIM2, 0); 该句不能加，加上灯不会按正常流程显示
DMA_Cmd(DMA1_Channel5, DISABLE);
DMA_ClearFlag(DMA1_FLAG_TC5);
}
// Input a value 0 to 255 to get a color value.
// The colours are a transition r - g - b - back to r.
uint32_t WS281x_Wheel(uint8_t wheelPos) {
wheelPos = 255 - wheelPos;
if(wheelPos < 85) {
return WS281x_Color(255 - wheelPos * 3, 0, wheelPos * 3);
}
if(wheelPos < 170) {
wheelPos -= 85;
return WS281x_Color(0, wheelPos * 3, 255 - wheelPos * 3);
}
wheelPos -= 170;
return WS281x_Color(wheelPos * 3, 255 - wheelPos * 3, 0);
}
// Fill the dots one after the other with a color
void WS281x_ColorWipe(uint32_t c, uint8_t wait) {
for(uint16_t i=0; i<PIXEL_NUM; i++) {
WS281x_SetPixelColor(i, c);
WS281x_Show();
delay_ms(wait);
}
}
void WS281x_Rainbow(uint8_t wait) {
uint16_t i, j;
for(j=0; j<256; j++) {
for(i=0; i<PIXEL_NUM; i++) {
WS281x_SetPixelColor(i, WS281x_Wheel((i+j) & 255));
}
WS281x_Show();
delay_ms(wait);
}
}
// Slightly different, this makes the rainbow equally distributed throughout
void WS281x_RainbowCycle(uint8_t wait) {
uint16_t i, j;
for(j=0; j<256*5; j++) { // 5 cycles of all colors on wheel
for(i=0; i< PIXEL_NUM; i++) {
WS281x_SetPixelColor(i,WS281x_Wheel(((i * 256 / PIXEL_NUM) + j) & 255));
}
WS281x_Show();
delay_ms(wait);
}
}
//Theatre-style crawling lights.
void WS281x_TheaterChase(uint32_t c, uint8_t wait) {
for (int j=0; j<10; j++) { //do 10 cycles of chasing
for (int q=0; q < 3; q++) {
for (uint16_t i=0; i < PIXEL_NUM; i=i+3) {
WS281x_SetPixelColor(i+q, c); //turn every third pixel on
}
WS281x_Show();
delay_ms(wait);
for (uint16_t i=0; i < PIXEL_NUM; i=i+3) {
WS281x_SetPixelColor(i+q, 0); //turn every third pixel off
}
}
}
}
//Theatre-style crawling lights with rainbow effect
void WS281x_TheaterChaseRainbow(uint8_t wait) {
for (int j=0; j < 256; j++) { // cycle all 256 colors in the wheel
for (int q=0; q < 3; q++) {
for (uint16_t i=0; i < PIXEL_NUM; i=i+3) {
WS281x_SetPixelColor(i+q, WS281x_Wheel( (i+j) % 255)); //turn every third pixel on
}
WS281x_Show();
delay_ms(wait);
for (uint16_t i=0; i < PIXEL_NUM; i=i+3) {
WS281x_SetPixelColor(i+q, 0); //turn every third pixel off
}
}
}
}