saml21/gpio: Allow multiple EXTI at the same time

[dylad]

This PR proposes a fix for #6904
To sum up, having one EXTI on saml21 works fine but if you try to enable several exti only the first one works.( all init said it's ok but only the first works)
The problem is any attempt to write into EIC->CONFIG failed after EIC is enabled (EIC->CTRLA.reg = EIC_CTRLA_ENABLE;)
SAML21 datasheet said that EIC->CONFIG registers are protected after EIC is enable. (27.6.2.1. Initialization -> page 473 of saml21 datasheet)

Another solution would be (disable EIC at the end of the function, change EIC->CONFIG reg and re-enable it):

    /* enable clocks for the EIC module */
    MCLK->APBAMASK.reg |= MCLK_APBAMASK_EIC;
    GCLK->PCHCTRL[EIC_GCLK_ID].reg = GCLK_PCHCTRL_CHEN | GCLK_PCHCTRL_GEN_GCLK0;
    /* enable the global EIC interrupt */
    NVIC_EnableIRQ(EIC_IRQn);
    /*Enable pin interrupt */
    EIC->INTFLAG.reg = (1 << exti);
    EIC->INTENSET.reg = (1 << exti);
    /* disable the EIC module*/
    EIC->CTRLA.reg = 0;
    while (EIC->SYNCBUSY.reg & EIC_SYNCBUSY_ENABLE) {}
    /* configure the active flank */
    EIC->CONFIG[exti >> 3].reg &= ~(0xf << ((exti & 0x7) * 4));
    EIC->CONFIG[exti >> 3].reg |=  (flank << ((exti & 0x7) * 4));
    /* enable the EIC module*/
    EIC->CTRLA.reg = EIC_CTRLA_ENABLE;
    while (EIC->SYNCBUSY.reg & EIC_SYNCBUSY_ENABLE) {}
    return 0;

Let me know what you think about it.

[dylad]

After looking at cpu/samd21, I'm wordering if this bug is also present on SAM(R/D)21.
I don't have the hardware to test it. Can someone help me to confirm it ?
If the bug is also present, I'll merged GPIO driver into sam0_common and fix the bug.

edit: typos

[photonthunder]

I just ran a test using a samd21g18a and two EXTI appeared to work fine with latest master:

    gpio_init_int(GPIO_PIN(PA, 19), GPIO_IN_PU, GPIO_FALLING, samd21ble_isr, _);
    gpio_irq_enable(GPIO_PIN(PA,19));
    gpio_init_int(GPIO_PIN(PB, 8), GPIO_IN_PU, GPIO_FALLING, testpin_isr, _);
    gpio_irq_enable(GPIO_PIN(PB,8));

Let me know if I am missing something or you want me to try something else...

[dylad]

@photonthunder Thanks a lot for testing it !
I just read the SAMD21 & SAML21 datasheet. In fact, this bug only affects the SAML21 family.
CONFIGn registers (and some others) are "enable-protected" for SAML21 (Module EIC must be disabled to write the register) but this is not the case for SAMD21.
Sorry I should have seen that earlier...

[dylad]

@photonthunder BTW, did you notice the call to gpio_irq_enable is useless as it is already done in gpio_init_int ?
But I don't know if it's a normal behavior...

[photonthunder]

@dylad thanks. I was troubleshooting because I couldn't get it to work initially and through those in. I took them out and it was still functional.

[aabadie]

@dylad, I have no strong opinion on the change and tend to give an ACK. Maybe other maintainers will have comments ? @haukepetersen ?

[haukepetersen]

ACK

[haukepetersen]

verified 2 exti lines simultaneously working on the saml21-xpro and Murdock is happy -> go