sanzaru / ibm-1401

IBM 1401 emulator in Swift

IBM 1401 Emulator in Swift

This project is some very early and inclomplete version of an IBM 1401 emulator written in Swift.

While studying the machine and finishing a simple hello world punch card code, it was hard for me to test my code as there are not many emulators for the machine and I was not able to make simh run at this time.

With the help of the amazing emulator of https://rolffson.de I was finally able to punch and run my code virtually on his software. Unfortunately, the project is only availble for Microsoft Windows and more a 3D simulation than a convinient emulator, so I descided to write my own...

⚠️ The whole emulator is incomplete. For now, not all opcodes are implemented and reading external files into the storage is not finished.

> Image: https://upload.wikimedia.org/wikipedia/commons/c/cb/BRL61-IBM_1401.jpg

More information about the machine itself: http://ibm-1401.info

Requirements

The code should run on any system that supports Swift 5.7 and higher.

The emulator depends on lib1401

Manual

Usage

Inside the project directory run: swift run

to start an emulator. You will be welcomed with a prompt where you can enter commands.

Emulator commands

Load program (l / load)

You can load external files with punch card code when providing an absolute path to the load command.

Example: l /some/absolute/path/to/a/file.cd

Without any file name a default hello world program will be loaded.

Start / Step (s / start)

This command emulates pressing the IBM 1401 start button in single step mode.

Run (r / run)

This command emulates pressing the IBM 1401 start button in run mode.

Dump storage (d / dump)

This command dumps the complete storage. Note that the output is in BCD mode.

Monitor (m / monitor)

This command dumps all registers and contents.

Reset (rst / reset)

Terminate execution cycle, reset core storage and registers. This command allows you to load and run another program.

Quit (q / quit)

Quit the emulator

Features

• Load arbitrary program from external file

• Parity and validity checks for registers

• Normal 1401 opcodes:

  • Set Word Mark (,)
  • Clear Storage (/)
  • Move (M)
  • Move Digit (D)
  • Move Zone (Y)
  • Halt (.)
  • Halt and branch (.)
  • No Operation (N)
  • Load (L)
  • Write a line (2) - Partially implemented
  • Clear word mark ())
  • Divide (()
  • Modify address (=)
  • Zero and add (&)
  • Add (A)
  • Branch or branch on indicator (B)
  • Compare (C)
  • Move numerical / digit (D)
  • Move characters and edit (E)
  • UNDOCUMENTED / UNCLEAR (G)
  • Zero and substract (-)
  • Move characters to record or group (P)
  • Subtract (S)
  • Branch if word mark and/or zone (V)
  • Move characters and supress zeros (Z)
  • Read a card (1)
  • Read a card and branch (1)
  • Write and read (3)
  • Punch a card (4)
  • Read and punch (5)
  • Write and punch (6)
  • Write, read and punch (7)

• Optioal opcodes:

  • Multiply ( )
  • Store B-Address register (H)
  • Store A-Address register (Q)
  • Branch if bit equal (W)
  • Move and insert zeros (X)
  • Start read feed (8)
  • Start punch feed (9)

• Tape:

  • Control unit (U)

• Printer:

  • Control carriage (F)

• Bits:

  • Move zone (Z)

  • Special:

    • Select stacker and other device controls (K)

  • 1460-Features:

    • Translate (T)