Here's the code with added printf statements:

DSTATUS disk_initialize(uint8_t drv) {
    uint8_t r;

    printf("\n\n### drv=%d\n\n", drv);
    if (drv) return RES_NOTRDY;

    r = spisdcard_init();
    spisdcard_deselect();

    printf("\n\n### r=%d\n\n", r);

    spisdcardstatus = r ? 0 : STA_NOINIT;
    printf("\n\nspisdcardstatus=%d\n\n", spisdcardstatus);
    return spisdcardstatus;
}

And here's the output to the console:


### drv=0



### r=1



spisdcardstatus=1