SoftwareSerial with SAMD21 after attachInterruptWakeup

Hardware
#1

Hi. There is some problem with SoftwareSerial on SAMD21 chip (Seeeduino XIAO board). After using attachInterruptWakeup (ArduinoLowPower library) SoftwareSerial do not receive data correctly (transmit works). I think it is related to reconfiguration of CGLK. Here is configuration that library performs:

static void configGCLK6()

{

    // enable EIC clock

    GCLK->CLKCTRL.bit.CLKEN = 0; //disable GCLK module

    while (GCLK->STATUS.bit.SYNCBUSY);

    GCLK->CLKCTRL.reg = (uint16_t) (GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN_GCLK6 | GCLK_CLKCTRL_ID( GCM_EIC )) ;  //EIC clock switched on GCLK6

    while (GCLK->STATUS.bit.SYNCBUSY);

    GCLK->GENCTRL.reg = (GCLK_GENCTRL_GENEN | GCLK_GENCTRL_SRC_OSCULP32K | GCLK_GENCTRL_ID(6));  //source for GCLK6 is OSCULP32K

    while (GCLK->STATUS.reg & GCLK_STATUS_SYNCBUSY);

    GCLK->GENCTRL.bit.RUNSTDBY = 1;  //GCLK6 run standby

    while (GCLK->STATUS.reg & GCLK_STATUS_SYNCBUSY);

    /* Errata: Make sure that the Flash does not power all the way down

        * when in sleep mode. */

    NVMCTRL->CTRLB.bit.SLEEPPRM = NVMCTRL_CTRLB_SLEEPPRM_DISABLED_Val;

}

Can anyone help with figuring out reason of such behaviour and solution of this problem?

I know that the simplest way is to use hardware UART but I want to know at least how to reconfigure GCLK (if it is the reason) by default to solve the problem with SoftwareSerial.
Thanks.

#2

Softwareserial uses interrupts and you probably have a conflict. You can get I2C UARTS at low cost and eliminate the interrupt problems. You can also switch to another arduino such as the MEGA that has 4 serial ports.

#3

Thanks for the answer. I'll take into account that it works on an interrupt basis.
As for another arduino module - problem with SoftwareSerial is not crucial. I have already created additional hardware UART instead I2C (using sercom2 on xiao). I'm just wondering if there is any way to fix this or configure GCLK by default. Unfortunately, I don't know anything about this.