asm_structure.md

Assembly Language for Emulated CPU

Assembly language for Emulated CPU project was created with idea of creating a simple, fully operational language.

This is why it only contains 4 addressing modes and 26 OP codes.

== ADDRESSING MODES ==

List of addressing modes: (number of addressing mode - name)

0 - CONST 
1 - REGISTER
2 - ADDRESS
3 - ADDRESS_IN_REGISTER

CONST - simply an integer literal, doesn't have any special syntax

REGISTER - this is how values are retrieved from registers. If register address is out of range, an exception is thrown. Syntax: [n], where n is a register address.

ADDRESS - used as a memory reference. Syntax: &n, where n is a memory address.

ADDRESS_IN_REGISTER - used for getting values from a memory address which is stored in a specific register. Syntax: &[n], where n is register address containing a memory address.

== OP CODES ==

Every command (with a few exceptions) is constructed like so: command with no parameters: COMMAND command with one parameter: COMMAND <addr_mode except CONST mode> command with two parameters: COMMAND <addr_mode except CONST mode>, <addr_mode>

Additionally, every CONST value can be replaced by LABEL which points at some place in the code. For example:

loop:
INC [1]
JMP loop

loop will be converted to 0 after compilation, because MOV is located at first address of a memory (0x0). Therefore, this code could be written as:

INC [1]
JMP 0

But this would raise a compilation error, because CONST values cannot be used as first arguments.

List of OP codes: (OP code number - mnemonic - arguments count)

0 - NOP    (0)
1 - HLT    (0)
2 - MOV    (2)
3 - JMP    (1, label)
4 - JE	   (1, label)
5 - JNE    (1, label)
6 - JL     (1, label)
7 - JLE    (1, label)
8 - JG     (1, label)
9 - JGE    (1, label)
10 - PUSH  (1)
11 - POP   (1)
12 - CALL  (1, label)
13 - INC   (1)
14 - DEC   (1)
15 - ADD   (2)
16 - SUB   (2)
17 - MUL   (2)
18 - DIV   (2)
19 - AND   (2)
20 - OR    (2)
21 - XOR   (2)
22 - NOT   (1)
23 - RSHFT (2)
24 - LSHFT (2)
25 - CMP   (2)

NOP - no operation, mostly used as a placeholder
HLT - stops processor. Sets isStopped flag
MOV - moves data from one place to another
JMP - jumps to a specified label
JE - jumps to a specified label if ZERO flag is set
JNE - jumps to a specified label if ZERO flag is cleared
JL - jumps to a specified label if NEGATIVE flag is set
JLE - jumps to a specified label if NEGATIVE or ZERO flag is set
JG - jumps to a specified label if CARRY flag is set
JGE - jumps to a specified label if CARRY or ZERO flag is set
PUSH - pushes data to the stack
POP - pops data from the stack
CALL - pushes an instruction pointer to the stack and jumps to a specified label
INC - increments data from a provided address
DEC - decrements data from a provided address
ADD - adds data from one address to data from other address and stores the result in the first address
SUB - subtracts data from one address from data from other address and stores the result in the first address
MUL - multiplies data from one address by data from other address and stores the result in the first address
DIV - divides data from one address by data from other address and stores the result in the first address
AND - performs bitwise AND on corresponding bits from two data addresses
OR - performs bitwise OR on corresponding bits from two data addresses
XOR - performs bitwise XOR on corresponding bits from two data addresses
NOT - negates all bits in data from provided address
RSHFT - shifts all bits in data from provided address n times to right
LSHFT - shifts all bits in data from provided address n times to left
CMP - compares data from one address with data from other address and sets flags in ALU
Every jump OP code modifies instruction pointer.

ALU flags:

ZERO flag
NEGATIVE flag
CARRY flag

Other:

IS_STOPPED flag
INSTRUCTION_POINTER