不管是普通定時器還是高級定時器，你用哪個通道，就在程序里用OC多少。比如CH3對應OC3
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;
TIM_OCInitStructure.TIM_Pulse=42;
TIM_OC4Init(TIM1, &TIM_OCInitStructure);
TIM_OC4PreloadConfig(TIM1, TIM_OCPreload_Enable);
之前就是因為這個沒有弄清楚，PWM波形沒有輸出，這是在通用定時器里出現的錯誤。
等把這個錯誤解決了以后，就開弄高級定時器，沒有想到在通用定時器可以出來的PWM程序，在高級定時器就沒有輸出，只是改變了定時器以及對應的IO口。經過各種查找，發現是少了一條語句
TIM_CtrlPWMOutputs(TIM1,ENABLE);
加上這條語句后，就有輸出了。
這就是通用定時器與高級定時器的PWM輸出的區別。
如果不想用定時器的時鍾源作為時基，而是想用外部的脈沖來作為時基，那就要加一條語句
TIM_ETRClockMode2Config(TIM3, TIM_ExtTRGPSC_OFF, TIM_ExtTRGPolarity_NonInverted, 0);
並且是將外部脈沖接在對應定時器的ETR引腳上。
下面是基本代碼
void TIM3_PWM_Init(u16 arr,u16 psc)
{
GPIO_InitTypeDef GPIO_InitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD|RCC_AHB1Periph_GPIOA, ENABLE);
GPIO_PinAFConfig(GPIOD,GPIO_PinSource2,GPIO_AF_TIM3);
GPIO_PinAFConfig(GPIOC,GPIO_PinSource9,GPIO_AF_TIM3);
TIM_ETRClockMode2Config(TIM3, TIM_ExtTRGPSC_OFF, TIM_ExtTRGPolarity_NonInverted, 0);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_25MHz;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_Init(GPIOD, &GPIO_InitStructure);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_25MHz;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP ;
GPIO_Init(GPIOC,&GPIO_InitStructure);
TIM_TimeBaseStructure.TIM_Prescaler=psc;
TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_Period=arr;
TIM_TimeBaseStructure.TIM_ClockDivision=TIM_CKD_DIV1;
TIM_TimeBaseInit(TIM3,&TIM_TimeBaseStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;
TIM_OCInitStructure.TIM_Pulse=1;
TIM_OC4Init(TIM3, &TIM_OCInitStructure);
TIM_OC4PreloadConfig(TIM3, TIM_OCPreload_Enable);
TIM_ARRPreloadConfig(TIM3,ENABLE);
TIM_Cmd(TIM3, ENABLE);
TIM_CtrlPWMOutputs(TIM3,ENABLE);
}
現在還有個問題就是高級定時器1為什么不能通過PA8（通道 1）輸出PWM，處理器是stm32f4ZGT6.