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"