High speed GPIO switching

[KKIM.6]

Hi. Everyone.

I'm trying to control external MUX using a GPIO pin in the STM32WB55 microcontroller.

Because of a limited number of PWM pins, I'm trying to use a GPIO pin for continuous regular switching.

My question is that even though the company said a maximum of 45 MHz (or 9 ns) is possible for the GPIO pin my code does not work properly (mux doesn't switch well without a 1 ms delay).

The mux speed is a possible maximum of 100 MHz. So, I do not doubt it's performance but it may be due to the too fast swithing of GPIO pin.

I need at least 1 us (1 MHz) switching speed. 

So, I wonder how can I give 1 us delay to the GPIO pin properly using IDE code?

[STea]

Hello @KKIM.6 ,

to insert a delay you need to use the systick to count down to your desired time this is done in HAL_Delay() function .

You can write your own delay function to wok in us as shown bellow :

void delay_us(uint32_t us)

{

uint32_t ticks = (HAL_RCC_GetHCLKFreq() / 1000000) * us; HAL_Delay(ticks);

}

void Systick_Config(void) {

/* Configure the SysTick timer to overflow every 1 us */

HAL_SYSTICK_Config(SystemCoreClock / 1000000);

/* Configure the SysTick timer clock source */

HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);

}

BR

[AScha.3 · Accepted solution]

1. the real switching speed on I/O depends on: 

- core speed + bus speed (to gpios )

- how you access port (HAL - slow, about 1us ; direct register write - fast, about 16ns posible )

- c compiler-> optimizer setting (-O2 or -Ofast )

to test it, make a small loop and check pin with DSO. then you see, what you get with your settings.

  while (1)
  {
	  // HAL_GPIO_WritePin(GPIOG, GPIO_PIN_4, GPIO_PIN_RESET);
	  GPIOG->BSRR = GPIO_PIN_4<<16;
	 //  HAL_GPIO_WritePin(GPIOG, GPIO_PIN_4, GPIO_PIN_SET);
	  GPIOG->BSRR = GPIO_PIN_4;

    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }

- try HAL and  direct access (just un-/comment )

[Tesla DeLorean]

How is that ever going to work??

The MCU is going to saturate completely before it gets anywhere near 1MHz interrupt rate.

Need to delta a free running counter in a spin loops.

For GPIO patterns pace GPIO+DMA with a TIM trigger at the desired pattern rate.