void spiDataRW (channel, byte_ref, len)
	int	channel
	SV *	byte_ref
	int	len
        PREINIT:
        I32* temp;
        PPCODE:
        temp = PL_markstack_ptr++;
        spiDataRW(channel, byte_ref, len);
        if (PL_markstack_ptr != temp) {
          PL_markstack_ptr = temp;
          XSRETURN_EMPTY;
        }
        return;