Processor Simulator

• Getting Started
  • Commands
    • Run a program
  • Debugging
    • Registers and/or memory data
• Architecture
• Registers
  • Status Register
• Instructions
  • Instruction Flow
  • Instruction Set
    • Instruction Formats
    • List of Instructions
      • Arithmetic
      • Data Transfer
      • Control-Flow
• Translator
  • Rules Syntax
  • Examples

Getting Started

Commands

Run a program

run <assembly-filename>
    [-s, --step-by-step](bool)        (run interactively step by step. default: false)
    [-d, --data-memory](string)       (filename where to save data memory once the program has finished)
    [-r, --registers-memory](string)  (filename where to save registers memory once the program has finished)

Sample: run samples/sample.txt --step-by-step --data-memory samples/sample.dat --registers-memory samples/sample.reg

Debugging

Registers and/or memory data

If the program is executed using the flag -s or --step-by-step you will be able to see the state of registers and/or data memory at the end of every step executed otherwise if the flag is not provided you will be able to see the final state at the end.

The following menu will be presented:

Press the desired key and then hit [ENTER]...
 - (R) to see registers memory
 - (D) to see data memory
 - (E) to exit and quit
 - (*) Any other key to continue

If selected R or D, the data will be displayed in the following format:

           0x00            0x04            0x08            0x0C
0x00    0x0000000A      0x0010000A      0x000C0000      0x00000000
0x10    0x000100E8      0x00000008      0x00000012      0x00000087
0x20    0x0000FF00      0x00000000      0x00D00068      0x002000A8
0x30    0x000000E8      0x0000C008      0x00000012      0x00000087
0x40    0x00000012      0x00000000      0x00100000      0x00000000
....

This format applies also if the flags for saving the memory into files by using --data-memory or --registers-memory

Architecture

The current pipeline architecture is based on a 3-stages pipeline:

• Fetch
• Decode
• Execute

The following diagram shows the components of the architecture along with the pipeline and the interaction with its components:

Registers

Name	Description
R0	Status Register
R1 - R31	General Purpose

Status Register

The status register corresponds to register R0

Bit	Label	Description
0	--	Not used
1	--	Not used
2	PF	Parity flag
3	--	Not used
4	--	Not used
5	--	Not used
6	ZF	Zero flag
7	SF	Sign flag
8	--	Not used
9	--	Not used
10	--	Not used
11	OF	Overflow flag
12-31	--	Not used

Instructions

Instruction Flow

   Human Readable  - it is the basic instruction in a assembly file) 
        |          - e.g ADD 14, 18, 14
        V  
     Go Object     - the assembly instruction is translated into a
        |            struct/object to be used by the processor
        V 
   Binary (32-bit) - then it is translated into a 32-bit integer accordignly to formats
        |          - this instruction will be stored in the instructions memory
        V 
     Go Object     - CPU will decode the instruction into an object again and it will
                     execute the instruction accordignly to the definitions

Instruction Set

Instruction Formats

The next tables shows the format structure of the instructions accordingly to the different types: R, I, J

Type	Format (32 bits)
R	Opcode (6)	Rd (5)	Rs (5)	Rt (5)	Shmt (5)	Func (6)

Type	Format (32 bits)
I	Opcode (6)	Rd (5)	Rs (5)	- I m m e d i a t e (1 6 b i t s) -

Type | Format (32 bits)|| -----|------------|----|| J | Opcode (6) | - - - - - - - - - - A d d r e s s (2 6 b i t s ) - - - - - - - - - - |

• All instructions are 32-bit long (1 word)
• Rs, Rt, and Rd are general purpose registers
• PC stands for the program counter address
• C denotes a constant (immediate)
• - denotes that those values do not care

List of Instructions

Aritmetic

• From Opcode 000000 to 001111

  Syntax | Description | Type | 31 ||||| 0 | Notes | ---------------|----------------|------|--------|----|----|-----|-----|-----|----------------------------| add Rd,Rs,Rt | Rd = Rs + Rt | R | 000000 | Rd | Rs | Rt | - | - | with overflow | addu Rd,Rs,Rt | Rd = Rs + Rt | R | 000001 | Rd | Rs | Rt | - | - | without overflow | sub Rd,Rs,Rt | Rd = Rs - Rt | R | 000010 | Rd | Rs | Rt | - | - | with overflow | subu Rd,Rs,Rt | Rd = Rs - Rt | R | 000011 | Rd | Rs | Rt | - | - | without overflow | addi Rd,Rs,C | Rd = Rs + C | I | 000100 | Rd | Rs | Immediate (16)||| immediate with overflow | addiu Rd,Rs,C | Rd = Rs + C | I | 000101 | Rd | Rs | Immediate (16)||| immediate without overflow | cmp Rd,Rs,Rt | Rd = Rs <=> Rt | R | 000110 | Rd | Rs | Rt | - | - | 1 s<t, 2 =, 4 s>t | mul Rd,Rs,Rt | Rd = Rs * Rt | R | 000111 | Rd | Rs | Rt | - | - | without overflow |

Data Transfer

• From Opcode 010000 to 011111

  Syntax | Description | Type | 31 ||||| 0 | Notes | ---------------|----------------|------|--------|----|----|------|-----|-----|-------------------------| lw Rd,Rs,C | Rd = M[Rs + C] | I | 010000 | Rd | Rs | Offset (16) ||| load M[Rs + C] into Rd | sw Rd,Rs,C | M[Rd + C] = Rs | I | 010001 | Rd | Rs | Offset (16) ||| store Rd into M[Rs + C] | lli Rd,C | Rd = C | I | 010010 | Rd | - | Immediate (16) ||| load lower immediate | sli Rd,C | M[Rd] = C | I | 010011 | Rd | - | Immediate (16) ||| store lower immediate | lui Rd,C | Rd = C << 16 | I | 010100 | Rd | - | Immediate (16) ||| load upper immediate | sui Rd,C | M[Rd] = C << 16| I | 010101 | Rd | - | Immediate (16) ||| store upper immediate |

Control-Flow

• From Opcode 100000 to 101111

  Syntax | Description | Type | 31 ||||| 0 | Notes | ---------------|-----------------|------|--------|----|----|------|-----|-----|----------------------| beq Rd,Rs,C | br on equal | I | 100000 | Rd | Rs | Immediate (16) ||| PC = PC + 4 + 4C | bne Rd,Rs,C | br on not equal | I | 100001 | Rd | Rs | Immediate (16) ||| PC = PC + 4 + 4C | blt Rd,Rs,C | br on less | I | 100010 | Rd | Rs | Immediate (16) ||| PC = PC + 4 + 4C | bgt Rd,Rs,C | br on greater | I | 100011 | Rd | Rs | Immediate (16) ||| PC = PC + 4 + 4C | j C | jump to C | J | 100100 | C Address (26) ||| PC = 4*C |

Translator

This application has a builtin translator that converts human readable assembly instructions into machine code, the available instructions allowed are the ones defined on the previous instructions section.

Rules Syntax

• Only one instruction allowed per line
• Comments prefix is ;
• Comments are allowed to be on a single line or after an instruction in the same line
• It does not care about the amount of empty spaces or tabs
• Branch labels must be on a single line
• No instructions allowed to be on the same line where the branch label is declared
• Blank lines are allowed

Examples

; Here are some comments on a new line

 PROCESS_LOOP:                      ; Here is a label followed by an inline comment
 ADDI    R1, R1, 1                  ; Here is a instruction along with its operands and an inline comment
                                    ; Here it is an empty line which is allowed followed by an inline comment
 ADD     R15, R15, R16              ; R15 += C[I]
 BLT     R1, R20, PROCESS_LOOP      ; Here is an instruction using a branch label followed by an inline comment