Samr30/gpio: Erasing then write mux can generate spurious IRQ

[biboc]

Description

Erasing then write mux can generate spurious IRQ from another gpio sharing same extint

Steps to reproduce the issue

Example with PA6 and PB22 which share extint[6]:

void irq(void)
{
    puts("IRQ");
}
int main(void)
{
    gpio_init_int(GPIO_PIN(PA,6), GPIO_IN, GPIO_RISING, (gpio_cb_t)irq, NULL);
    gpio_mux_t mux = GPIO_MUX_D;
    gpio_t pin = GPIO_PIN(PB,22);
    int pin_pos = _pin_pos(pin); // use _pin_pos from gpio.c
    PortGroup* port = _port(pin); // use _port from gpio.c
    while(1) {
        xtimer_usleep(500000);
        port->PMUX[pin_pos >> 1].reg &= ~(0xf << (4 * (pin_pos & 0x1)));
        port->PMUX[pin_pos >> 1].reg |=  (mux << (4 * (pin_pos & 0x1)));
    }
    return 0;
}

This code triggers some time (maybe 2sec, maybe 20sec) an IRQ on PA6!
I can confirm that the line PA6 stays to always 0 so there should not be any IRQ

I suggest to change /~https://github.com/RIOT-OS/RIOT/blob/2023.10-branch/cpu/sam0_common/periph/gpio.c#L147

void gpio_init_mux(gpio_t pin, gpio_mux_t mux)
{
    PortGroup* port = _port(pin);
    int pin_pos = _pin_pos(pin);

    port->PINCFG[pin_pos].reg |= PORT_PINCFG_PMUXEN;
    port->PMUX[pin_pos >> 1].reg &= ~(0xf << (4 * (pin_pos & 0x1)));
    port->PMUX[pin_pos >> 1].reg |=  (mux << (4 * (pin_pos & 0x1)));
}

by

void gpio_init_mux(gpio_t pin, gpio_mux_t mux)
{
    PortGroup* port = _port(pin);
    int pin_pos = _pin_pos(pin);

    port->PINCFG[pin_pos].reg |= PORT_PINCFG_PMUXEN;
    if (pin_pos & 1) {
        port->PMUX[pin_pos >> 1].bit.PMUXO = mux;
    } else {
        port->PMUX[pin_pos >> 1].bit.PMUXE = mux;
    }
}

Expected results

Set the mux without trigger an interrupt

Actual results

Trigger non desired interrupt

Versions

RIOT 2023-07

[dylad]

Sorry for the long delay @biboc
Are you using SAMR30-XPRO or a custom board ?
Were you able to reproduce on another SAM0 MCUs ?

I tried to reproduce it on my SAMR21-XPRO and SAML21-XPRO (don't have SAMR30). I kinda reproduce it because my hand touch to EXT1 connector where the PA06 is located triggering unexpected IRQs. Setting a pull-down with the PA06 IRQ seems to fix it.

Otherwise I was not able to reproduce any spurious IRQ after flashing your code snippet (and nothing else) to these boards (and make sure I was far away this time...)

Does it help to disable the mux configuration for your pin before modifying it ? like:

    port->PINCFG[pin_pos].reg &= ~PORT_PINCFG_PMUXEN;
    port->PMUX[pin_pos >> 1].reg &= ~(0xf << (4 * (pin_pos & 0x1)));
    port->PMUX[pin_pos >> 1].reg |=  (mux << (4 * (pin_pos & 0x1)));
    port->PINCFG[pin_pos].reg |= PORT_PINCFG_PMUXEN;