DMA 独立计数法推荐多轴高频场景零脉冲开销为了释放CPU可以利用 TIM8 4个通道各自独立的Compare (CC) DMA请求。让硬件DMA去数脉冲CPU只在脉冲发送完毕时介入一次。实现机制定时器每次输出一个PWM脉冲发生比较匹配时触发一次通道的DMA请求。DMA将一个“无用数据”搬运到“无用地址”纯为了消耗DMA自身的传输计数器NDTR。当NDTR减到0时触发DMA传输完成中断TC我们在DMA的中断中关闭PWM输出。DMA通道映射TIM8_CH1 - DMA2_Stream2 (Channel 7)TIM8_CH2 - DMA2_Stream3 (Channel 7)TIM8_CH3 - DMA2_Stream4 (Channel 7)TIM8_CH4 - DMA2_Stream7 (Channel 7)测试代码这是一个基于 STM32 标准外设库SPLStandard Peripheral Library的完整 C 和 H 代码实现。tim8_pwm_dma.h#ifndef __TIM8_PWM_DMA_H #define __TIM8_PWM_DMA_H #include stm32f4xx.h // 定义控制通道 typedef enum { AXIS_CH1 1, AXIS_CH2 2, AXIS_CH3 3, AXIS_CH4 4 } TIM8_Channel_e; // 外部调用接口 void TIM8_PWM_DMA_Init(void); void TIM8_Output_Pulses(TIM8_Channel_e channel, uint32_t pulses); #endif /* __TIM8_PWM_DMA_H */tim8_pwm_dma.c#include tim8_pwm_dma.h /* * 假负载目标地址DMA只需要每次脉冲触发时搬运一次数据来消耗 NDTR 计数器 * 因此将数据搬运到这些无意义的变量中。 */ static uint16_t dummy_dst[4] {0, 0, 0, 0}; /** * brief 初始化 GPIO, TIM8 及对应 DMA2 * note 使用引脚 PC6, PC7, PC8, PC9 (AF3) 输出 TIM8 CH1-CH4 */ void TIM8_PWM_DMA_Init(void) { GPIO_InitTypeDef GPIO_InitStructure; TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure; TIM_OCInitTypeDef TIM_OCInitStructure; DMA_InitTypeDef DMA_InitStructure; NVIC_InitTypeDef NVIC_InitStructure; /* 1. 使能时钟 */ RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC | RCC_AHB1Periph_DMA2, ENABLE); RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM8, ENABLE); /* 2. 配置 GPIO (PC6 - PC9 复用为 TIM8) */ GPIO_PinAFConfig(GPIOC, GPIO_PinSource6, GPIO_AF_TIM8); GPIO_PinAFConfig(GPIOC, GPIO_PinSource7, GPIO_AF_TIM8); GPIO_PinAFConfig(GPIOC, GPIO_PinSource8, GPIO_AF_TIM8); GPIO_PinAFConfig(GPIOC, GPIO_PinSource9, GPIO_AF_TIM8); GPIO_InitStructure.GPIO_Pin GPIO_Pin_6 | GPIO_Pin_7 | GPIO_Pin_8 | GPIO_Pin_9; GPIO_InitStructure.GPIO_Mode GPIO_Mode_AF; GPIO_InitStructure.GPIO_Speed GPIO_Speed_100MHz; GPIO_InitStructure.GPIO_OType GPIO_OType_PP; GPIO_InitStructure.GPIO_PuPd GPIO_PuPd_DOWN ; GPIO_Init(GPIOC, GPIO_InitStructure); /* 3. 配置 TIM8 基础时基 (这里假设 APB284MHz, TIM8 Clk168MHz. 生成 10kHz 频率) */ TIM_TimeBaseStructure.TIM_Prescaler 168 - 1; // 1MHz 计数频率 TIM_TimeBaseStructure.TIM_Period 100 - 1; // 10kHz PWM 频率 TIM_TimeBaseStructure.TIM_ClockDivision TIM_CKD_DIV1; TIM_TimeBaseStructure.TIM_CounterMode TIM_CounterMode_Up; TIM_TimeBaseStructure.TIM_RepetitionCounter 0; TIM_TimeBaseInit(TIM8, TIM_TimeBaseStructure); /* 4. 配置 TIM8 输出比较 (PWM1 模式初始占空比 50%) */ TIM_OCInitStructure.TIM_OCMode TIM_OCMode_PWM1; TIM_OCInitStructure.TIM_OutputState TIM_OutputState_Disable; // 初始关闭需要时打开 TIM_OCInitStructure.TIM_OutputNState TIM_OutputNState_Disable; TIM_OCInitStructure.TIM_Pulse 50; // 50% 占空比 TIM_OCInitStructure.TIM_OCPolarity TIM_OCPolarity_High; TIM_OCInitStructure.TIM_OCIdleState TIM_OCIdleState_Reset; TIM_OC1Init(TIM8, TIM_OCInitStructure); TIM_OC1PreloadConfig(TIM8, TIM_OCPreload_Enable); TIM_OC2Init(TIM8, TIM_OCInitStructure); TIM_OC2PreloadConfig(TIM8, TIM_OCPreload_Enable); TIM_OC3Init(TIM8, TIM_OCInitStructure); TIM_OC3PreloadConfig(TIM8, TIM_OCPreload_Enable); TIM_OC4Init(TIM8, TIM_OCInitStructure); TIM_OC4PreloadConfig(TIM8, TIM_OCPreload_Enable); TIM_CtrlPWMOutputs(TIM8, ENABLE); // 使能主输出 MOE TIM_Cmd(TIM8, ENABLE); // 开启定时器计数此时还没有脉冲因为 CCxE 为 0 /* 5. 配置 DMA2 公共基础参数 */ DMA_DeInit(DMA2_Stream2); DMA_DeInit(DMA2_Stream3); DMA_DeInit(DMA2_Stream4); DMA_DeInit(DMA2_Stream7); DMA_InitStructure.DMA_Channel DMA_Channel_7; // TIM8 CH1-CH4 在 DMA2 中均为 Channel 7 DMA_InitStructure.DMA_DIR DMA_DIR_PeripheralToMemory; // 必须是外设到内存响应定时器请求 DMA_InitStructure.DMA_PeripheralInc DMA_PeripheralInc_Disable; DMA_InitStructure.DMA_MemoryInc DMA_MemoryInc_Disable; // 不自增反复写一个假地址 DMA_InitStructure.DMA_PeripheralDataSize DMA_PeripheralDataSize_HalfWord; DMA_InitStructure.DMA_MemoryDataSize DMA_MemoryDataSize_HalfWord; DMA_InitStructure.DMA_Mode DMA_Mode_Normal; // 单次传输发完即停 DMA_InitStructure.DMA_Priority DMA_Priority_High; DMA_InitStructure.DMA_FIFOMode DMA_FIFOMode_Disable; DMA_InitStructure.DMA_FIFOThreshold DMA_FIFOThreshold_1QuarterFull; DMA_InitStructure.DMA_MemoryBurst DMA_MemoryBurst_Single; DMA_InitStructure.DMA_PeripheralBurst DMA_PeripheralBurst_Single; /* 配置各通道 DMA 的源地址和目标地址 */ // CH1: DMA2_Stream2 DMA_InitStructure.DMA_PeripheralBaseAddr (uint32_t)(TIM8-CCR1); DMA_InitStructure.DMA_Memory0BaseAddr (uint32_t)dummy_dst[0]; DMA_Init(DMA2_Stream2, DMA_InitStructure); // CH2: DMA2_Stream3 DMA_InitStructure.DMA_PeripheralBaseAddr (uint32_t)(TIM8-CCR2); DMA_InitStructure.DMA_Memory0BaseAddr (uint32_t)dummy_dst[1]; DMA_Init(DMA2_Stream3, DMA_InitStructure); // CH3: DMA2_Stream4 DMA_InitStructure.DMA_PeripheralBaseAddr (uint32_t)(TIM8-CCR3); DMA_InitStructure.DMA_Memory0BaseAddr (uint32_t)dummy_dst[2]; DMA_Init(DMA2_Stream4, DMA_InitStructure); // CH4: DMA2_Stream7 DMA_InitStructure.DMA_PeripheralBaseAddr (uint32_t)(TIM8-CCR4); DMA_InitStructure.DMA_Memory0BaseAddr (uint32_t)dummy_dst[3]; DMA_Init(DMA2_Stream7, DMA_InitStructure); /* 6. 配置 DMA 中断 (NVIC) */ NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority 1; NVIC_InitStructure.NVIC_IRQChannelSubPriority 0; NVIC_InitStructure.NVIC_IRQChannelCmd ENABLE; NVIC_InitStructure.NVIC_IRQChannel DMA2_Stream2_IRQn; NVIC_Init(NVIC_InitStructure); NVIC_InitStructure.NVIC_IRQChannel DMA2_Stream3_IRQn; NVIC_Init(NVIC_InitStructure); NVIC_InitStructure.NVIC_IRQChannel DMA2_Stream4_IRQn; NVIC_Init(NVIC_InitStructure); NVIC_InitStructure.NVIC_IRQChannel DMA2_Stream7_IRQn; NVIC_Init(NVIC_InitStructure); } /** * brief 启动指定通道输出特定数量的脉冲 * param channel: AXIS_CH1 ~ AXIS_CH4 * param pulses: 目标脉冲数量 */ void TIM8_Output_Pulses(TIM8_Channel_e channel, uint32_t pulses) { if(pulses 0) return; switch(channel) { case AXIS_CH1: // 1. 关闭通道和DMA请求 TIM8-CCER ~TIM_CCER_CC1E; TIM_DMACmd(TIM8, TIM_DMA_CC1, DISABLE); DMA_Cmd(DMA2_Stream2, DISABLE); // 2. 配置新的传输数量并清标志 DMA_SetCurrDataCounter(DMA2_Stream2, pulses); DMA_ClearFlag(DMA2_Stream2, DMA_FLAG_TCIF2 | DMA_FLAG_HTIF2 | DMA_FLAG_TEIF2); // 3. 开启 DMA 传输完成中断 DMA_ITConfig(DMA2_Stream2, DMA_IT_TC, ENABLE); // 4. 按顺序重新使能 DMA - TIM_DMA - TIM_CCxE 开启输出 DMA_Cmd(DMA2_Stream2, ENABLE); TIM_DMACmd(TIM8, TIM_DMA_CC1, ENABLE); TIM8-CCER | TIM_CCER_CC1E; break; case AXIS_CH2: TIM8-CCER ~TIM_CCER_CC2E; TIM_DMACmd(TIM8, TIM_DMA_CC2, DISABLE); DMA_Cmd(DMA2_Stream3, DISABLE); DMA_SetCurrDataCounter(DMA2_Stream3, pulses); DMA_ClearFlag(DMA2_Stream3, DMA_FLAG_TCIF3 | DMA_FLAG_HTIF3 | DMA_FLAG_TEIF3); DMA_ITConfig(DMA2_Stream3, DMA_IT_TC, ENABLE); DMA_Cmd(DMA2_Stream3, ENABLE); TIM_DMACmd(TIM8, TIM_DMA_CC2, ENABLE); TIM8-CCER | TIM_CCER_CC2E; break; case AXIS_CH3: TIM8-CCER ~TIM_CCER_CC3E; TIM_DMACmd(TIM8, TIM_DMA_CC3, DISABLE); DMA_Cmd(DMA2_Stream4, DISABLE); DMA_SetCurrDataCounter(DMA2_Stream4, pulses); DMA_ClearFlag(DMA2_Stream4, DMA_FLAG_TCIF4 | DMA_FLAG_HTIF4 | DMA_FLAG_TEIF4); DMA_ITConfig(DMA2_Stream4, DMA_IT_TC, ENABLE); DMA_Cmd(DMA2_Stream4, ENABLE); TIM_DMACmd(TIM8, TIM_DMA_CC3, ENABLE); TIM8-CCER | TIM_CCER_CC3E; break; case AXIS_CH4: TIM8-CCER ~TIM_CCER_CC4E; TIM_DMACmd(TIM8, TIM_DMA_CC4, DISABLE); DMA_Cmd(DMA2_Stream7, DISABLE); DMA_SetCurrDataCounter(DMA2_Stream7, pulses); DMA_ClearFlag(DMA2_Stream7, DMA_FLAG_TCIF7 | DMA_FLAG_HTIF7 | DMA_FLAG_TEIF7); DMA_ITConfig(DMA2_Stream7, DMA_IT_TC, ENABLE); DMA_Cmd(DMA2_Stream7, ENABLE); TIM_DMACmd(TIM8, TIM_DMA_CC4, ENABLE); TIM8-CCER | TIM_CCER_CC4E; break; } } /* 中断服务函数 */ void DMA2_Stream2_IRQHandler(void) { // CH1 DMA 传输完成 if (DMA_GetITStatus(DMA2_Stream2, DMA_IT_TCIF2) ! RESET) { TIM8-CCER ~TIM_CCER_CC1E; // 核心瞬间切断硬件输出使能 TIM_DMACmd(TIM8, TIM_DMA_CC1, DISABLE);// 停止DMA请求 DMA_ClearITPendingBit(DMA2_Stream2, DMA_IT_TCIF2); } } void DMA2_Stream3_IRQHandler(void) { // CH2 DMA 传输完成 if (DMA_GetITStatus(DMA2_Stream3, DMA_IT_TCIF3) ! RESET) { TIM8-CCER ~TIM_CCER_CC2E; TIM_DMACmd(TIM8, TIM_DMA_CC2, DISABLE); DMA_ClearITPendingBit(DMA2_Stream3, DMA_IT_TCIF3); } } void DMA2_Stream4_IRQHandler(void) { // CH3 DMA 传输完成 if (DMA_GetITStatus(DMA2_Stream4, DMA_IT_TCIF4) ! RESET) { TIM8-CCER ~TIM_CCER_CC3E; TIM_DMACmd(TIM8, TIM_DMA_CC3, DISABLE); DMA_ClearITPendingBit(DMA2_Stream4, DMA_IT_TCIF4); } } void DMA2_Stream7_IRQHandler(void) { // CH4 DMA 传输完成 if (DMA_GetITStatus(DMA2_Stream7, DMA_IT_TCIF7) ! RESET) { TIM8-CCER ~TIM_CCER_CC4E; TIM_DMACmd(TIM8, TIM_DMA_CC4, DISABLE); DMA_ClearITPendingBit(DMA2_Stream7, DMA_IT_TCIF7); } }主函数测试#include sys.h #include delay.h #include stm32f4xx.h #include stm32f4xx_conf.h #include tim8_pwm_dma.h int main(void) { TIM8_PWM_DMA_Init(); while(1) { TIM8_Output_Pulses(AXIS_CH1,21); delay_ms(20); } }使用仿真测试平台实现效果如下一次发出了21个PWM脉冲