stm32f103: a timer triggering DMA to update another timer's CCR using libopencm3

Question

I'm playing with the blue pill.

Here I run TIM2 and enable the DMA on its update event, according to Table 78 of RM0008, the DMA channel I should use is channel 2 on DMA1. Then I want the DMA to update TIM1.CCR1.

But I cannot get it working around DMA part. Here is the code:

#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/stm32/timer.h>
#include <libopencm3/stm32/dma.h>

#define PHASE_SIZE  10

const unsigned short PWM_phase[PHASE_SIZE] = {
  1, 11, 21, 31, 41, 51, 61, 71, 81, 91
};

int main(void) {
  // setup TIM1 as the main output
  rcc_periph_clock_enable(RCC_TIM1);
  rcc_periph_clock_enable(RCC_GPIOA);
  rcc_periph_clock_enable(RCC_AFIO);
  gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, GPIO8);
  timer_set_mode(TIM1, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP);
  timer_set_oc_mode(TIM1, TIM_OC1, TIM_OCM_PWM1);
  timer_enable_oc_output(TIM1, TIM_OC1);
  timer_enable_oc_preload(TIM1, TIM_OC1);
  timer_enable_break_main_output(TIM1);
  timer_set_oc_value(TIM1, TIM_OC1, 30);
  timer_set_period(TIM1, 120);
  timer_enable_counter(TIM1);

  // setup DMA
  rcc_periph_clock_enable(RCC_DMA1);
  dma_set_peripheral_address(DMA1, DMA_CHANNEL2, (uint32_t)TIM1_CCR1);
  dma_set_memory_address(DMA1, DMA_CHANNEL2, (uint32_t)&PWM_phase[0]);
  dma_set_number_of_data(DMA1, DMA_CHANNEL2, PHASE_SIZE);
  dma_set_priority(DMA1, DMA_CHANNEL2, DMA_CCR_PL_MEDIUM);
  dma_set_read_from_memory(DMA1, DMA_CHANNEL2);
  dma_set_memory_size(DMA1, DMA_CHANNEL2, DMA_CCR_MSIZE_16BIT);
  dma_set_peripheral_size(DMA1, DMA_CHANNEL2, DMA_CCR_MSIZE_16BIT);
  dma_enable_memory_increment_mode(DMA1, DMA_CHANNEL2);
  dma_disable_peripheral_increment_mode(DMA1, DMA_CHANNEL2);
  dma_enable_circular_mode(DMA1, DMA_CHANNEL2);
  dma_enable_channel(DMA1, DMA_CHANNEL2);

  // setup TIM2 
  rcc_periph_clock_enable(RCC_TIM2);
  timer_set_mode(TIM2, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP);
  timer_set_period(TIM2, 100);
  timer_set_dma_on_update_event(TIM2);
  timer_enable_counter(TIM2);

  while(1) {
    //__asm("nop");
  }
}

I can read through openocd that the TIM2 is ticking. But when the RCC_DMA is enabled, I cannot read DMA registers anymore (may be they are busy?).

Is there something wrong with DMA setup? Thank you!

And there is no libopencm3 tag yet?

Answer 1

you have 2 issues. First, You must give TIM1_CCR1 address, I recommend to use the macro TIM_CCR1() for this task:

dma_set_peripheral_address(DMA1, DMA_CHANNEL2, (uint32_t)&TIM_CCR1(TIM1));

Second, You are forgetting to enable the update event in the TIM2 config:

timer_enable_irq(TIM2, TIM_DIER_UDE);

Good luck!