topic Re: GPIO input detection via M7-core in i.MX Processors

GPIO input detection via M7-core

pratham_malaviya — Wed, 05 Feb 2025 15:42:04 GMT

Hi there,

We are implementing a system in which we are detecting up to 1 MHz of PWM signal on the input GPIO pin.

Now the issue we are facing is high read latencies.

Here are test cases with the approaches I used:

First, we took a pair of input and output GPIOs.

Approach-1: Polling

Keep reading the state of the input GPIO and copy it to the output GPIO.
Tested Frequencies: 100 kHz, 500 kHz, and 1 MHz.
Fast slew rate of output GPIO.
Tried implementing bare metal instead of wrapper functions.

Conclusion:

Till 100 kHz it works fine, but on higher frequencies there are hard delays of around ~1.5. us.

Approach-2: Using Interrupt

Configure the input pin as an IRQ source, and when the rising edge is detected, toggle the output GPIO from ISR.

Conclusion:

Same as the polling approach when the PWM frequency was at 500 kHz. The interrupts were missed.

So, my queries are as below:

What are the causes of these hard delays?
Is it theoretically possible to do what we are trying?
Any other possible approach you can suggest>

Thanks and regards,

Pratham.

Re: GPIO input detection via M7-core

Manuel_Salas — Thu, 06 Feb 2025 02:33:22 GMT

Hello @pratham_malaviya

I hope you are doing very well.

Theoretically, It should be possible, but accessing GPIOs through the general-purpose I/O registers (even when using bare metal) has inherent latencies due to memory access overhead.

You can try to use RTOS and use the taskENTER_CRITICAL() function and measure if there is an improvement.

I hope this can helps to you.

Best regards,

Salas.

Re: GPIO input detection via M7-core

pratham_malaviya — Thu, 06 Feb 2025 11:54:55 GMT

Hi @Manuel_Salas ,

Thank you for your support!

As per your suggestion, I implemented it using RTOS, but some hard delays still remain.

I am attaching a code snippet and a logic analyzer capture for your reference.

Channel-1: Output GPIO
Channel-2: PWM signal fed to input GPIO.

I am still confused about these hard delays. The clock root for the GPIO is around 133 MHz, yet register access still takes a significant amount of time.

static void hello_task(void *pvParameters) { for (;;) { // PRINTF("Hello world.\r\n"); taskENTER_CRITICAL(); state = GPIO_PinRead(INPUT_GPIO,INPUT_GPIO_PIN); GPIO_PinWrite(EXAMPLE_LED_GPIO,EXAMPLE_LED_GPIO_PIN,state); taskEXIT_CRITICAL(); // vTaskSuspend(NULL); } }

Re: GPIO input detection via M7-core

pratham_malaviya — Thu, 13 Feb 2025 13:23:03 GMT

Hi @Manuel_Salas ,
Any update on above issue?

Regards,

Pratham