版主你好，作为初涉STM32的新手，正在尝试利用DMA向外设传递数据的操作，在使用官方例程时发现一个奇怪的问题。
我采用的是STM32F207下的DMABurst例程（代码贴在最后），利用TIM1的输出一个PWM信号，通过示波器的确可以看到在PA.8端口有5.8KHz的脉冲波形输出，且占空比为33％。但在脉冲波形开始输出前，有2us的时间输出的是16MHz的脉冲波形。通过程序跟踪，发现在执行了TIM_Config()语句后就出现了这个波形，这是什么原因呢？
另外，我实际想尝试的是用TIM定时中断来触发DMA向GPIO端口输出信号，对例程做了修改可没有成功，应该是对TIM与DMA的理解不是很清楚，想找有关这方面的资料，在哪里可以找到呢？
代码如下：
/*
This example shows how to update the TIM1 channel1 period and the duty cycle
using the TIM1 DMA burst feature.
Every update DMA request, the DMA will do 3 transfers of half words into Timer
registers beginning from ARR register.
On the DMA update request, 0x0FFF will be transferred into ARR, 0x0000
will be transferred into RCR, 0x0555 will be transferred into CCR1. */
#define TIM1_DMAR_ADDRESS ((uint32_t)0x4001004C) /* TIM DMAR address */
/* Private variables ---------------------------------------------------------*/
GPIO_InitTypeDef GPIO_InitStructure;
DMA_InitTypeDef DMA_InitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
uint16_t SRC_Buffer[6] = {0x0FFF, 0x0000, 0x0555};
/* Private function prototypes -----------------------------------------------*/
void TIM_Config(void);
/* Private functions ---------------------------------------------------------*/
/**
* @brief Main program
* @param None
* @retval None
*/
int main(void)
{
/*!< At this stage the microcontroller clock setting is already configured,
this is done through SystemInit() function which is called from startup
file (startup_stm32f2xx.s) before to branch to application main.
To reconfigure the default setting of SystemInit() function, refer to
system_stm32f2xx.c file
*/
/* TIM1 Configuration */
TIM_Config();
/* Time base configuration */
/* -----------------------------------------------------------------------
TIM1 Configuration: generate 1 PWM signal using the DMA burst mode:
The TIM1CLK frequency is set to SystemCoreClock (Hz), to get TIM1 counter
clock at 24 MHz the Prescaler is computed as following:
- Prescaler = (TIM1CLK / TIM1 counter clock) - 1
SystemCoreClock is set to 120 MHz
The TIM1 period is 5.8 KHz: TIM1 Frequency = TIM1 counter clock/(ARR + 1)
= 24 MHz / 4096 = 5.8KHz KHz
TIM1 Channel1 duty cycle = (TIM1_CCR1/ TIM1_ARR)* 100 = 33.33%
----------------------------------------------------------------------- */
TIM_TimeBaseStructure.TIM_Period = 0xFFFF;
TIM_TimeBaseStructure.TIM_Prescaler = (uint16_t) (SystemCoreClock / 24000000) - 1;
TIM_TimeBaseStructure.TIM_ClockDivision = 0x0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
/* TIM Configuration in PWM Mode */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0xFFF;
TIM_OC1Init(TIM1, &TIM_OCInitStructure);
/* TIM1 DMAR Base register and DMA Burst Length Config */
TIM_DMAConfig(TIM1, TIM_DMABase_ARR, TIM_DMABurstLength_3Transfers);
/* TIM1 DMA Update enable */
TIM_DMACmd(TIM1, TIM_DMA_Update, ENABLE);
/* TIM1 enable */
TIM_Cmd(TIM1, ENABLE);
/* TIM1 PWM Outputs Enable */
TIM_CtrlPWMOutputs(TIM1, ENABLE);
/* Enable DMA2 Stream5 */
DMA_Cmd(DMA2_Stream5, ENABLE);
/* Wait until DMA2 Stream5 end of Transfer */
while (!DMA_GetFlagStatus(DMA2_Stream5, DMA_FLAG_TCIF5))
{
}
/* Infinite loop */
while(1)
{
}
}
/**
* @brief Configure the TIM1 Pins.
* @param None
* @retval None
*/
void TIM_Config(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
/* TIM1 clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);
/* GPIOA clock enable */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
/* DMA2 clock enable */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);
/* GPIOA Configuration: PA8(TIM1 CH1) as alternate function push-pull ------*/
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
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_NOPULL;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* Connect TIM pins to AF1 */
GPIO_PinAFConfig(GPIOA, GPIO_PinSource8, GPIO_AF_TIM1);
/* DeInitialize the DMA2 Stream5 */
DMA_DeInit(DMA2_Stream5);
DMA_InitStructure.DMA_Channel = DMA_Channel_6;
DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)TIM1_DMAR_ADDRESS;
DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)SRC_Buffer;
DMA_InitStructure.DMA_DIR = DMA_DIR_MemoryToPeripheral;
DMA_InitStructure.DMA_BufferSize = 3;
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_VeryHigh;
DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Enable;
DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_Full;
DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;
DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
DMA_Init(DMA2_Stream5, &DMA_InitStructure);
} |
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