Von Neumann machine emulator

Downloading

Builds for Windows and Linux are available here.

Building

$ mkdir build && cd build
$ cmake ..
$ cmake --build . --config Release

Requires compiler fully supporting std::filesystem.

Usage

$ ./von-neumann [OPTION...]

  -h, --help         Show help
  -f, --file arg     Path to the VNM program file
  -c, --counter arg  Set initial program counter value
  -s, --save         Save output to file
  -r, --register     Print register values before every cycle
  -m, --memory       Print memory before every cycle
  -b, --binary       Print instruction arguments in binary
  -d, --signed       Print instruction arguments as 9-bit signed integers

Example:

$ ./von-neumann -rmf example/array_sum.vnm

Machine properties

• Memory of 512 16-bit words, addressed from 0 to 511.

• Four 16-bit registers

  • Accumulator (AC)
  • Operand register (OR)
  • Program counter (PC)
  • Instruction register (IR)

Available instructions

• STOP , code: 0000, stops the machine
• LOAD , code: 0001, operation: AC = OR
• STORE, code: 0010, operation: MEM[ OR ] = AC
• JUMP , code: 0011, operation: PC = OR
• JNEG , code: 0100, operation: AC < 0 => PC = OR
• JZERO, code: 0101, operation: AC == 0 => PC = OR
• ADD , code: 0110, operation: AC = AC + OR
• SUB , code: 0111, operation: AC = AC - OR
• MULT, code: 1000, operation: AC = AC * OR
• DIV , code: 1001, operation: AC = AC / OR
• AND , code: 1010, operation: AC = AC & OR
• OR , code: 1011, operation: AC = AC | OR
• NOT , code: 1100, operation: AC = ~OR
• CMP , code: 1101, operation: AC == OR => AC = -1,AC != OR => AC = 0
• SHZ , code: 1110, operation: OR < 0 => AC >> |OR|, OR > 0 => AC << |OR|
• SHC , code: 1111, circular shift left or right, depending on the sign of the operand

Available addressing modes

• Instant, code: 00, $, operation: OR = IR.arg
• Direct, code: 01, @, operation: OR = MEM[ IR.arg ]
• Indirect, code: 10, &, operation: OR = MEM[ MEM[ IR.arg ] ]
• Index, code: 11, +, operation: OR = MEM[ AC + IR.arg ]

Word interpretation

• 16 bits
  • Most significant bit - farthest to the left left, unused
  • Next four bits - instruction code (IR.code)
  • Next two bits - addressing mode code (IR.mode)
  • Remaining nine bits - instruction argument (IR.arg)

Examples

Doubling the sum of a pair of numbers

0. LOAD  @ 5 ; instructions begin
1. ADD   @ 6 ;
2. MULT  $ 2 ;
3. STORE $ 7 ;
4. STOP      ; instructions end
5. 21        ; first data
6. 34        ; second data
7. 0         ; result

Summation of the array with indirect addressing

0.  LOAD  $ 0
1.  STORE $ 19
2.  LOAD  $ 21
3.  STORE $ 18
4.  LOAD  $ 21
5.  ADD   @ 20
6.  SUB   @ 18
7.  JZERO $ 15
8.  LOAD  @ 19
9.  ADD   & 18
10. STORE $ 19
11. LOAD  @ 18
12. ADD   $ 1
13. STORE $ 18
14. JUMP  $ 4
15. STOP
16. 
17. 
18.     ; auxiliary memory
19.     ; result
20. 5   ; number of elements in sequence: n
21. 10  ; first element:  array[ 0 ]
22. 20  ; second element: array[ 1 ]
23. 30  ; ...
24. 40  ; ...
25. 50  ; last element:   array[ n - 1 ]

Reference

Machine specification was based on Przykładowa maszyna cyfrowa (PMC) as defined in the book below.

Kawa, R., & Lembas, J. (2017). "Wykłady z informatyki: Wstęp do informatyki". Warszawa: Wydawnictwo Naukowe PWN.