Activate the RF field and probe for a Type A Target.

        The PN531 can discover some Type A Targets (Type 2 Tag and
        Type 4A Tag) at 106 kbps. Type 1 Tags (Jewel/Topaz) are
        completely unsupported. Because the firmware does not evaluate
        the SENS_RES before sending SDD_REQ, it may be that a warning
        message about missing Type 1 Tag support is logged even if a
        Type 2 or 4A Tag was present. This typically happens when the
        SDD_RES or SEL_RES are lost due to communication errors
        (normally when the tag is moved away).

def sense_tta(self, target):
        """Activate the RF field and probe for a Type A Target.

        The PN531 can discover some Type A Targets (Type 2 Tag and
        Type 4A Tag) at 106 kbps. Type 1 Tags (Jewel/Topaz) are
        completely unsupported. Because the firmware does not evaluate
        the SENS_RES before sending SDD_REQ, it may be that a warning
        message about missing Type 1 Tag support is logged even if a
        Type 2 or 4A Tag was present. This typically happens when the
        SDD_RES or SEL_RES are lost due to communication errors
        (normally when the tag is moved away).

        """
        target = super(Device, self).sense_tta(target)
        if target and target.sdd_res and len(target.sdd_res) > 4:
            # Remove the cascade tag(s) from SDD_RES, only the PN531
            # has them included and we've set the policy that cascade
            # tags are not part of the sel_req/sdd_res parameters.
            if len(target.sdd_res) == 8:
                target.sdd_res = target.sdd_res[1:]
            elif len(target.sdd_res) == 12:
                target.sdd_res = target.sdd_res[1:4] + target.sdd_res[5:]
            # Also the SENS_RES bytes are reversed compared to PN532/533
            target.sens_res = bytearray(reversed(target.sens_res))
        return target