rxm – DEC RX02 Floppy Disk System Emulator

The rxm program is an emulator for the Digital Equipment Corporation RX02 Floppy Disk System, presenting a faithful representation of RX01 or RX02 dual floppy drives to a host computer. It requires a physical interface module connecting a PC parallel port to an RX disk interface card (schematics available from the author). The emulator has been shown to operate with various OS/8, RT-11 handlers, and 2.11BSD drivers.

rxm can be configured via command-line options at initiation or dynamically during emulation. An interrupt signal (typically ^C) stops emulation and presents a command prompt, allowing users to modify attached disk images for drives 0 and 1 (e.g., 0 filename), change emulation/transfer types, adjust verbosity, print status, or quit. The emulator has interruptible and uninterruptible states; caution is advised when interacting with the prompt while in an uninterruptible state due to potential disk image corruption.

Key command-line options include specifying the emulation type (-t RX01, RX02, RX03), transfer mode (-t DMA, PIO), assigning image files to drive units 0 and 1 (-0 filename, -1 filename), setting image density (-d SD, DD), and expanding image files (-X).

The emulator's real-time bit-banging of serial data stream requires significant processing power, recommending a dedicated machine (e.g., 400Mhz Pentium II) for optimal performance. Although the RX01/02 protocol is drive-paced, some host handlers and boot loaders may violate it, causing issues. A known bug involves RT11 boot hangs, where an empty buffer command after a disk read can be lost due to timing inconsistencies with the RX_DONE bit.