HelenOS sources

XHCI_LEGSUP_SEM_BIOS  426 uspace/drv/bus/usb/xhci/hc.c 		    XHCI_REG_RD(hc->legsup, XHCI_LEGSUP_SEM_BIOS),
XHCI_LEGSUP_SEM_BIOS  428 uspace/drv/bus/usb/xhci/hc.c 		if (XHCI_REG_RD(hc->legsup, XHCI_LEGSUP_SEM_BIOS) == 0) {
HelenOS homepage, sources at GitHub