title: stm32f446 When using dma to control PWM duty cycle, the PWM wave has abnormal waveform
body: <p>MCU: f446rct6
  System: freertos
  Library: hal</p>
  <p>Program logic:</p>
  <ol>
  <li>Initialize the timer to output the PWM wave and initialize the DMA and connect to the Capture/Compare register</li>
  <li>Start the timer</li>
  <li>When data needs to be updated, start a dma transmission</li>
  </ol>
  <p>Phenomenon: There is no problem with the frequency and duty cycle of the PWM wave, but a strange triangular waveform often appears in the first or second waveform of DMA transmission.</p>
  <p>Ask everyone, do you encounter similar waveforms when using pwm? Please give me a hint to locate this problem, thank you</p>
  <p><img src="https://i.stack.imgur.com/HVsrH.jpg" alt="Pin's output oscilloscope trace" /></p>