Sorry, but there is currently no provision for this in A-Shell/Linux (other than using the AUXLOC: device to print back to an ATE client with a client-resident printer init file specifying a
DUPLEX option).
The only way I can imagine duplex printing direct from Linux to the printer working would be via an lpr filter and associated command line switch, which, if you can find the right combination, could be specified in the
DEVICE statement of the printer init file.
Adding a DUPLEX flag to the
switches parameter of
XCALL SPOOL would be a bit of a stretch, since there are more than one option, thus it would require multiple bits.