Psions communicate using the Psion Link Protocol (PLP). Reconnect builds on top of plptools, a tried-and-tested open source implementation of PLP for posix-friendly systems.
plptools comprises the following components:
ncpd—daemon that manages the connection to a single Psion on a serial port and exposes the different services to the local machine over TCPplpftp—CLI offering an FTP-like interface for browsing and transferring filesplpfuse—exposes the connected Psion as local file system using FUSE
plpprint—print-server allowing you to print-to-files from your Psionsisinstall—CLI for installing SIS installer files on EPOC32 devicesgraph TD
plpftp --> ncpd
plpfuse --> ncpd
plpprint --> ncpd
sisinstall --> ncpd
Unfortunately, the evolving security architecture of macOS is increasingly hostile to services like FUSE (you need to disable System Integrity Protection to install the required kernel extensions), and having to manually run services like ncpd to manage your Psion connection is far from user-friendly, necessitating a different approach on macOS.