Hello,
I want to generate an arbitrary waveform by a timer using DMA. The waveform is using different pulse widths and also varying periods in multiples of 25µs.
By reading AN4776 and HAL documentation I figured out it should be possible with HAL_TIM_DMABurst_MultiWriteStart() function. Unfortunately I don't get an output signal except after reset where a short pulse can be seen. I assume this pulse is due to port configuration during initialization. After that pulse, the signal stays high.
My setup (CubeMX):
- Nucleo32-L432, core clock 80MHz
- Used timer is Tim16
- Prescaler is set to 399 => 80 MHz / 400 = 5µs resolution
- ARR and CCR preload enabled
- ARR and CCR set to 0 (initialized in source code)
- DMA enabled
- normal mode
- memory to peripheral
- Word / Word
- increment address on memory
- interrupt enabled
For a first run I want to use fixed pulse widths and varying periods, so all my code does is the following:
/* USER CODE BEGIN 2 */
htim16.Instance->ARR = 39; //40 * 5µs = 200µs period
htim16.Instance->CCR1 = 4; //5 * 5µs = 25µs pulse
HAL_TIM_DMABurst_MultiWriteStart(&htim16, TIM_DMABASE_ARR, TIM_DMA_UPDATE, (uint32_t *) Buffer, TIM_DMABURSTLENGTH_1TRANSFER, sizeof(Buffer) / sizeof(Buffer[0]));
HAL_TIM_PWM_Start(&htim16, TIM_CHANNEL_1);
/* USER CODE END 2 */
As far as I understood I need to initiate the first pulse by calling HAL_TIM_PWM_Start() and HAL_TIM_DMABurst_MultiWriteStart() setup the DMA to handle the subsequent transfers.
When running that code, I get a single pulse of ~3.4µs at a period of 5.8µs, after that the output stays high. Since this is my first encounter with DMA I'm a bit lost. I don't get what I'm missing because other forum entries use basically the same approach as far as I can see.
Regards
