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rust-neander

Do you want the easiest way to learning virtual machine and assembly? You've found it!

rust-neander is a virtual machine that runs assembly Neander and Neander+!

They are very didactic hypothetical machines. It is useful if you want to learn more about how a CPU works and how to write a simple assembly code, because Neander and Neander+ were developed in order to be simple for beginners. You will learn these languages and hypothetical machines in a few minutes!

Neander hypothetic machine

  • memory size: 256
  • 8-bit to data width and addresses
  • datas are represented using complement two (if the bit 7 is turn on, the number is negative)
  • one accumalator with 8-bit (AC)
  • one program counter with 8-bit (PC)
  • one status register with 2 condition codes: negative (N) and zero (Z)

Neander+ hypothetic machine

This machine is the same of the above plus:

  • 256 registers to input data (accessible with the IN operator)

Assembly

Both assembly have few operators. Neander+ is compatible with Neander and it has a little more operators.

Neander

Hex code Instruction Description
00 ... 1F NOP No operation
10 ... 1F STA address Store the value from AC at the address
20 ... 2F LDA address Load at AC the value from the address
30 ... 3F ADD address Add the AC plus the value from the address
40 ... 4F OR address Use the OR binary operator with AC and the value from the address
50 ... 5F AND address Use the AND binary operator with AC and the value from the address
60 ... 6F NOT Use the NOT binary operator with AC
80 ... 8F JMP value Load at PC the value
90 ... 9F JN value If AC is a negative value, load at PC the value
A0 ... AF JZ value If AC is zero, load at PC the value
F0 ... FF HLT Finish the execution

If it tries to execute an nonexistent operator, such as 7A, it will raise an error.

Example to sum 2 and 3:

Address Hex code
00 20
01 05
02 30
03 06
04 FF
05 02
06 03

Neander+

Neander+ has five more operators than Neander: SUB, JNZ, IN, OUT, LDI. The remaining operators are the same as the ones Neander has.

Neander+ was inspirated in Neander-X

Hex code Instruction Description
70 ... 7F SUB address Sub the AC with the value from the address
B0 ... BF JNZ value If AC is not zero, load at PC the value
C0 ... CF IN index Load at AC the value the input at the index
D0 ... DF OUT Copy the AC at the out
E0 ... EF LDI value Store at AC the value

Example to duplicate the value at first position of the input and output the result:

Address Hex code
00 C0
01 00
02 10
03 07
04 30
05 07
06 FF
07 00

How to execute

To execute your code (for example, that you wrote at ndp/example.ndp file), you can execute it using:

> cargo run ndp/example.ndp

And, to set the inputs used in IN instruction:

> cargo run ndp/example.ndp -i="02 0A"