hm-asm

A small assembler I wrote for use with the microprocessor from the Book "Grundlagen der Technische Informatik" by Dirk W. Hoffmann.

This microprocessor has a single accumulator register that calculations use.

Syntax

The processor supports the following commands:

Instruction	Coding	Description
NOP	0000	No operation
LDA #n	0001	Load value n to accumulator
LDA (n)	0010	Load value from address n to accumulator
STA (n)	0011	Store value from accumulator to address n
ADD #n	0100	Add value n to accumulator
ADD (n)	0101	Add value from address n to accumulator
SUB #n	0110	Subtract value n from accumulator
SUB (n)	0111	Subtract value from address n from accumulator
JMP n	1000	Jump to program counter n
BRZ #n	1001	Branch n instructions relative to current instruction when zero bit is set
BRC #n	1010	Branch n instructions relative to current instruction when carry bit is set
BRN #n	1010	Branch n instructions relative to current instruction when negative bit is set

Each instruction is eight bit large: four bit for the opcode and four bit for the operand. The instruction is split into program memory (opcode) and data memory (operand).

Three state bits of the previous arithmetic operation can be used in control flow: Negative, Carry and Zero.

You can find some syntax examples for the assembler in examples/

Limitations

The operand size of four bits limits the directly addressable memory to 16 instructions. This generally limits the memory size, while large program memory is supported. Furthermore since the operands of the instructions are stored in the same part of memory as where you can store values with the STA instruction it is technically possible to overwrite your program operands at runtime and do a sort of self modifying programming style, this assembler does not warn you if you do this as of now.

Project structure

The project consists of 3 main components:

• hm-asm-simulator is a Rust library that contains the parsing, compilation and simulation logic
• hm-asm-cli is a CLI frontend for hm-asm-simulator
• hm-asm-web is a WebAssemly library frontend for hm-asm-simulator

For more information regarding the specific sub components refer to their individual READMEs