stm32 PWM产生

/* TIM Configuration */

  TIM_Config();

  TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);

  TIM_OCStructInit(&TIM_OCInitStructure);

  /* ---------------------------------------------------------------------------

     TIM8 is configured to generate an Asymetric signal with a programmable

     Phase-Shifted signal on TIM8_CH2:

     - TIM8 Channel 1 is configured in PWM2 mode

     - TIM8 Channel 2 is configured in Asymetric PWM2 mode

     - The counter mode is center aligned mode

     - The pulse length and the phase shift are programmed consecutively in TIM8_CCR2 and TIM8_CCR1.

     TIM1 is configured to generating the reference signal on Channel1 used by TIM8:

     - TIM1 is generating a PWM signal with frequency equal to 1.5KHz

     - TIM1 is used as master for TIM8, the update event of TIM1 genarates the Reset counter

     of TIM8 to synchronize the two signals: the reference signal (TIM1_CH1) and

            the shifted signal (TIM8_CH2).

    In this example TIM1 and TIM8 input clock (TIM18CLK) is set to APB2 clock (PCLK2)

    TIM1 and TIM8 signals are at frequency of (SystemCoreClock / (PWM_FREQUENCY + 1))

    TIM8 is gerating a signal with the following caracteristics:

     - Pulse lenght = (TIM8_CCR1 + TIM8_CCR2) / TIM8_CLK

     - Phase shift = TIM8_CCR1/TIM8_CLK

     with TIM8_CLK = (SystemCoreClock / (Period + 1)), as the prescaler is equal to zero.

    Note:

     SystemCoreClock variable holds HCLK frequency and is defined in system_stm32f30x.c file.

     Each time the core clock (HCLK) changes, user had to call SystemCoreClockUpdate()

     function to update SystemCoreClock variable value. Otherwise, any configuration

     based on this variable will be incorrect.

  --------------------------------------------------------------------------- */

  /* Initialize Timers: TIM1 & TIM8 */

  /* Time base configuration for TIM8 and TIM1 */

  TIM_TimeBaseStructure.TIM_Period = PWM_FREQUENCY;     //

  TIM_TimeBaseStructure.TIM_Prescaler = 0;        // this prescaler is 1

  TIM_TimeBaseStructure.TIM_ClockDivision = 0;

  /* First wrong parameter: Counting Mode,TIM8 counting direction has to be set to center-aligned mode */

  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_CenterAligned1;

  TIM_TimeBaseInit(TIM8, &TIM_TimeBaseStructure);

    //??????????TIM8?????ì???????????ú????·??????è??????????????·?????????·???????????????????????

  TIM_TimeBaseStructure.TIM_Period = 2 * PWM_FREQUENCY;        // 1??PWM?¨???????è?¨

  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);

  /* Channels 1&2 configuration on TIM8 */

  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;

  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;

  TIM_OCInitStructure.TIM_Pulse = INITIAL_PHASE;

  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;

  TIM_OC1Init(TIM8, &TIM_OCInitStructure); /* Channel1 config done */

  /* Second wrong parameter: PWM Mode */

  /* The same PWM mode has to be configured for the two coupled channels */

  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Asymmetric_PWM2;

  TIM_OCInitStructure.TIM_Pulse = INITIAL_LENGTH;

  TIM_OC2Init(TIM8, &TIM_OCInitStructure); /* Channel2 config done */

  /* Channel1 configuration on TIM1 */

  TIM_OCInitStructure.TIM_Pulse = 2 * PWM_FREQUENCY / 10 * 0.9;        // 2??PWM ????±?

  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;

  TIM_OC1Init(TIM1, &TIM_OCInitStructure);

  /* Enable outputs on both TIM1 & TIM8*/

  TIM_CtrlPWMOutputs(TIM8, ENABLE);

  TIM_CtrlPWMOutputs(TIM1, ENABLE);

  /* Synchronization between TIM1 and TIM8

  The aim is to generate a reference signal on TIM1_CH1

  The Phase-Shifted siganl generated on TIM8_CH2 is compared to the reference

  signal

  */

  TIM_SelectSlaveMode(TIM8, TIM_SlaveMode_Reset); /* Configure TIM8 in slave

  mode: an active edge on trigger input generates a reset on tIM8 */

  TIM_SelectInputTrigger(TIM8, TIM_TS_ITR0); /* Connect TIM1 to TIM8

  TIM1 is the Master

  TIM8 is the Slave */

  TIM_SelectOutputTrigger(TIM1,TIM_TRGOSource_Update); /* Select the Update

  to be the Master Trigger-Out TRGO signal origine */

  TIM_CCPreloadControl(TIM8, ENABLE); /* Enable Shadaw register on TIM8

  CCRx register are not accessed directly: their content is updated each Update

  event */

  /* TIM8 enable counter */

  TIM_Cmd(TIM1, ENABLE);

  TIM_Cmd(TIM8, ENABLE)