Trigger TIM2 using a GPIO as external trigger

[SKrey.1]

Hi,

on a STM32L451CE I try to make use of TIM2 timer. I want to start this timer on an external trigger event. From the device datasheet I know that the pin PA0 can be used with AF14 as a TIM2_ETR. However when I setup the timer it doesnt start counting, although I received a rising edge on that line. Can you help me why its not start counting?

Here are the relevant code parts I've written to enable the mechanism:

#define TIM2_CCMR1 (volatile uint32_t *) (TIM2_BASE + 0x18)
#define TIM2_CCER (volatile uint16_t *) (TIM2_BASE + 0x20)
#define TIM2_SMCR (volatile uint32_t *) (TIM2_BASE + 0x08)
 
 
void Init()
{
	LL_GPIO_StructInit(&GPIO_InitStruct);
	// Serializier BNE
	GPIO_InitStruct.Pin = LL_GPIO_PIN_0;
	GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
	GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_VERY_HIGH;
	GPIO_InitStruct.Pull = LL_GPIO_PULL_NO;
	GPIO_InitStruct.Alternate = LL_GPIO_AF_14;
	LL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 
	LL_APB1_GRP1_EnableClock(LL_APB1_GRP1_PERIPH_TIM2);
	
	*TIM2_CCMR1 &= 0xFFFFFFFC;
 *TIM2_CCMR1 |= 0x1;
 *TIM2_CCER &= 0xFFFFFFFC;
 *TIM2_CCER |= 0x2;
 *TIM2_SMCR &= 0xFFFFFFF8;
 *TIM2_SMCR |= 0x6;
 *TIM2_SMCR &= 0xFFFFFF8F;
 *TIM2_SMCR |= 0x50;
}

What am I missing here?

Any help is appreciated, if you need additional info please let me know.

Thanks, Steve

[waclawek.jan]

For ETR, you need to set SMCR.TS=0b111.

Read out and check/post the content of TIM2 and the relevant GPIO registers. Did you enable TIM2 and GPIOA clock in RCC?

Style: why don't you use symbols, or at least the peripherals' struts (ie. TIM2->CCER etc.), defined in the device header?

JW

[SKrey.1]

Hello Jan,

thanks for your answer. Yeah setting SMCR.TS to 111 seems to do it.

However I wonder if my approach is correct overall. What I actually want to do is to trigger a DMA transfer for SPI transmit, however I want that the DMA is not triggered based on TXE event but on an external trigger (via a PIN). Would this be possible via the timers? I mean I got it counting now, however what I actually want is to forward this event to the DMA. What kind of peripheral request I should choose for the DMA? And what mode to choose for the timer so that the event can be forwarded to the DMA in order to trigger SPI transmission?

@style, yeah I couldn't found any abstraction this is why I choosed to define the addresses for my own, however I'll have a look at the header file.

Thanks for any hints on this issue.

[waclawek.jan]

> What kind of peripheral request I should choose for the DMA?

TIMx_DIER.TDE

> @style, yeah I couldn't found any abstraction

I don't know what do you mean by "abstraction" here. Maybe you meant examples. It's a shame ST does not provide clean examples, they just promote the Cube stuff. A request for this here, please vote if you agree. Examples e.g. see 'F0/'L0 Snippets at ST, the same as appendix in 'F0/'L0 RMs, I have some at efton dot sk, there are more out there if you search.

JW

[SKrey.1]

Hi,

no with the term "abstraction" I was referring to symbols to use instead of my own macros. Anyway thanks for the answer.

Can you also give me a hint which dma / channel to use ? Is it DMA1.Ch5 request 0110 ? (Table 41 of the TRM)

Thanks, Steve

[waclawek.jan]

Steve,

My copy of RM0394 rev4 Tab.41 shows no connection on DMA1/Ch5/sel.0110... Can you please recheck/post a screenshot?

Actually, I see no DMA trigger for TIM2_TRG, so you may want to use the other AF from the same pin to TIM2_CH1 and trigger DMA from that.

JW