# AMD64 Quad-Core CPU Implementation

## Folder Structure
```
amd64_cpu/
├── src/
│   ├── core/
│   │   ├── amd64_core.sv
│   │   ├── fetch_unit.sv
│   │   ├── decode_unit.sv
│   │   ├── execute_unit.sv
│   │   ├── memory_unit.sv
│   │   └── writeback_unit.sv
│   ├── thread/
│   │   ├── thread_scheduler.sv
│   │   └── thread_context.sv
│   ├── interconnect/
│   │   ├── bus_interconnect.sv
│   │   └── cache_controller.sv
│   ├── memory/
│   │   ├── l1_cache.sv
│   │   └── l2_cache.sv
│   └── top_level/
│       └── amd64_cpu_top.sv
├── testbench/
│   ├── tb_amd64_cpu.sv
│   └── tb_core.sv
└── README.md
```

## Core Files

### 1. Top Level Module - `src/top_level/amd64_cpu_top.sv`
```verilog
`timescale 1ps/1ps

module amd64_cpu_top (
    input wire clk,
    input wire rst_n,
    input wire [63:0] instr_bus,
    input wire [63:0] data_bus_in,
    output reg [63:0] data_bus_out,
    output reg busy
);

    // Core instances
    wire [63:0] core0_instr, core1_instr, core2_instr, core3_instr;
    wire [63:0] core0_data_out, core1_data_out, core2_data_out, core3_data_out;
    
    // Thread control signals
    wire [3:0] thread_active;
    wire [3:0] thread_ready;
    
    // Core interconnect
    wire [63:0] shared_l2_cache_data_in, shared_l2_cache_data_out;
    wire [63:0] shared_l2_cache_addr;
    wire shared_l2_cache_we;
    wire shared_l2_cache_req;
    wire shared_l2_cache_ack;
    
    // Core instances
    amd64_core core0 (
        .clk(clk),
        .rst_n(rst_n),
        .instr_in(core0_instr),
        .data_in(data_bus_in),
        .data_out(core0_data_out),
        .busy(busy)
    );
    
    amd64_core core1 (
        .clk(clk),
        .rst_n(rst_n),
        .instr_in(core1_instr),
        .data_in(data_bus_in),
        .data_out(core1_data_out),
        .busy(busy)
    );
    
    amd64_core core2 (
        .clk(clk),
        .rst_n(rst_n),
        .instr_in(core2_instr),
        .data_in(data_bus_in),
        .data_out(core2_data_out),
        .busy(busy)
    );
    
    amd64_core core3 (
        .clk(clk),
        .rst_n(rst_n),
        .instr_in(core3_instr),
        .data_in(data_bus_in),
        .data_out(core3_data_out),
        .busy(busy)
    );
    
    // Thread scheduler
    thread_scheduler scheduler (
        .clk(clk),
        .rst_n(rst_n),
        .thread_active(thread_active),
        .thread_ready(thread_ready),
        .core0_instr(core0_instr),
        .core1_instr(core1_instr),
        .core2_instr(core2_instr),
        .core3_instr(core3_instr)
    );
    
    // Shared L2 Cache
    l2_cache cache (
        .clk(clk),
        .rst_n(rst_n),
        .data_in(shared_l2_cache_data_in),
        .data_out(shared_l2_cache_data_out),
        .addr(shared_l2_cache_addr),
        .we(shared_l2_cache_we),
        .req(shared_l2_cache_req),
        .ack(shared_l2_cache_ack)
    );
    
    // Bus interconnect
    bus_interconnect interconnect (
        .clk(clk),
        .rst_n(rst_n),
        .data_in(data_bus_in),
        .data_out(data_bus_out),
        .core0_data_out(core0_data_out),
        .core1_data_out(core1_data_out),
        .core2_data_out(core2_data_out),
        .core3_data_out(core3_data_out)
    );
    
endmodule
```

### 2. Core Module - `src/core/amd64_core.sv`
```verilog
`timescale 1ps/1ps

module amd64_core (
    input wire clk,
    input wire rst_n,
    input wire [63:0] instr_in,
    input wire [63:0] data_in,
    output reg [63:0] data_out,
    output reg busy
);

    // Pipeline stages
    reg [63:0] pc;
    reg [63:0] instruction;
    
    // Control signals
    reg fetch_en;
    reg decode_en;
    reg execute_en;
    reg memory_en;
    reg writeback_en;
    
    // Register file
    reg [63:0] registers[0:31];
    
    // ALU outputs
    reg [63:0] alu_result;
    reg alu_zero;
    reg alu_carry;
    
    // Memory unit
    reg [63:0] memory_data;
    reg memory_write_enable;
    
    // Pipeline control
    reg pipeline_stall;
    
    // Fetch stage
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            pc <= 64'h0000000000000000;
        end else if (fetch_en && !pipeline_stall) begin
            pc <= pc + 8; // 64-bit instruction size
        end
    end
    
    // Decode stage
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            instruction <= 64'h0000000000000000;
        end else if (decode_en && !pipeline_stall) begin
            instruction <= instr_in;
        end
    end
    
    // Execute stage
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            alu_result <= 64'h0000000000000000;
            alu_zero <= 1'b0;
            alu_carry <= 1'b0;
        end else if (execute_en && !pipeline_stall) begin
            // Simple ALU operations for demonstration
            case (instruction[31:25])
                7'h20: begin // ADD
                    alu_result <= registers[instruction[19:15]] + registers[instruction[24:20]];
                    alu_zero <= (alu_result == 0);
                end
                7'h28: begin // SUB
                    alu_result <= registers[instruction[19:15]] - registers[instruction[24:20]];
                    alu_zero <= (alu_result == 0);
                end
                default: begin
                    alu_result <= registers[instruction[19:15]];
                    alu_zero <= (registers[instruction[19:15]] == 0);
                end
            endcase
        end
    end
    
    // Memory stage
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            memory_data <= 64'h0000000000000000;
            memory_write_enable <= 1'b0;
        end else if (memory_en && !pipeline_stall) begin
            // Memory access logic
            memory_data <= data_in;
            memory_write_enable <= instruction[31]; // Assume bit 31 indicates write
        end
    end
    
    // Writeback stage
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            data_out <= 64'h0000000000000000;
        end else if (writeback_en && !pipeline_stall) begin
            data_out <= alu_result;
        end
    end
    
    // Pipeline control logic
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            fetch_en <= 1'b0;
            decode_en <= 1'b0;
            execute_en <= 1'b0;
            memory_en <= 1'b0;
            writeback_en <= 1'b0;
            busy <= 1'b0;
        end else begin
            fetch_en <= 1'b1;
            decode_en <= fetch_en;
            execute_en <= decode_en;
            memory_en <= execute_en;
            writeback_en <= memory_en;
            
            // Busy signal - core is busy if pipeline has instructions
            busy <= (fetch_en || decode_en || execute_en || memory_en || writeback_en);
        end
    end
    
endmodule
```

### 3. Thread Scheduler - `src/thread/thread_scheduler.sv`
```verilog
`timescale 1ps/1ps

module thread_scheduler (
    input wire clk,
    input wire rst_n,
    input wire [3:0] thread_active,
    input wire [3:0] thread_ready,
    output reg [63:0] core0_instr,
    output reg [63:0] core1_instr,
    output reg [63:0] core2_instr,
    output reg [63:0] core3_instr
);

    // Thread scheduling state machine
    typedef enum reg [1:0] {
        SCHED_IDLE = 2'b00,
        SCHED_DISPATCH = 2'b01,
        SCHED_WAIT = 2'b10
    } sched_state_t;
    
    sched_state_t current_state, next_state;
    
    // Round-robin scheduling
    reg [1:0] current_thread;
    reg [3:0] available_threads;
    
    // Thread instruction selection
    reg [63:0] thread_instructions[0:3];
    
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            current_state <= SCHED_IDLE;
            current_thread <= 2'b00;
            available_threads <= 4'b1111;
            core0_instr <= 64'h0000000000000000;
            core1_instr <= 64'h0000000000000000;
            core2_instr <= 64'h0000000000000000;
            core3_instr <= 64'h0000000000000000;
        end else begin
            // Update state machine
            current_state <= next_state;
            
            // Dispatch instructions to cores based on thread availability
            case (current_state)
                SCHED_IDLE: begin
                    if (available_threads != 4'b0000) begin
                        next_state <= SCHED_DISPATCH;
                    end else begin
                        next_state <= SCHED_WAIT;
                    end
                end
                
                SCHED_DISPATCH: begin
                    // Round-robin dispatch
                    case (current_thread)
                        2'b00: core0_instr <= thread_instructions[0];
                        2'b01: core1_instr <= thread_instructions[1];
                        2'b10: core2_instr <= thread_instructions[2];
                        2'b11: core3_instr <= thread_instructions[3];
                    endcase
                    
                    next_state <= SCHED_IDLE;
                    current_thread <= (current_thread + 1) % 4;
                end
                
                SCHED_WAIT: begin
                    if (available_threads != 4'b0000) begin
                        next_state <= SCHED_DISPATCH;
                    end else begin
                        next_state <= SCHED_WAIT;
                    end
                end
            endcase
            
            // Update available threads based on ready status
            available_threads <= thread_ready & thread_active;
        end
    end
    
endmodule
```

### 4. Bus Interconnect - `src/interconnect/bus_interconnect.sv`
```verilog
`timescale 1ps/1ps

module bus_interconnect (
    input wire clk,
    input wire rst_n,
    input wire [63:0] data_in,
    output reg [63:0] data_out,
    input wire [63:0] core0_data_out,
    input wire [63:0] core1_data_out,
    input wire [63:0] core2_data_out,
    input wire [63:0] core3_data_out
);

    // Arbitration logic for multiple masters
    reg [3:0] arbitration_priority;
    reg [3:0] master_select;
    
    // Data multiplexer
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            data_out <= 64'h0000000000000000;
            arbitration_priority <= 4'b1111; // Highest priority to core 0
        end else begin
            // Simple round-robin arbitration
            master_select <= arbitration_priority;
            
            case (master_select)
                4'b0001: data_out <= core0_data_out;
                4'b0010: data_out <= core1_data_out;
                4'b0100: data_out <= core2_data_out;
                4'b1000: data_out <= core3_data_out;
                default: data_out <= 64'h0000000000000000;
            endcase
            
            // Update arbitration priority
            arbitration_priority <= {arbitration_priority[2:0], arbitration_priority[3]};
        end
    end
    
endmodule
```

### 5. L2 Cache - `src/memory/l2_cache.sv`
```verilog
`timescale 1ps/1ps

module l2_cache (
    input wire clk,
    input wire rst_n,
    input wire [63:0] data_in,
    output reg [63:0] data_out,
    input wire [63:0] addr,
    input wire we,
    input wire req,
    output reg ack
);

    // Cache parameters
    parameter CACHE_SIZE = 1024; // 1KB cache
    parameter LINE_SIZE = 64;    // 64 bytes per line
    
    // Cache memory array
    reg [63:0] cache_memory[0:1023];
    
    // Cache state
    reg valid_bit [0:1023];
    reg dirty_bit [0:1023];
    reg [31:0] tag_bits [0:1023];
    
    // Cache control signals
    reg cache_hit;
    reg cache_miss;
    reg cache_valid;
    
    // Address decoding
    wire [9:0] cache_index;  // Assuming 64-byte lines
    wire [31:0] cache_tag;
    
    assign cache_index = addr[15:6];
    assign cache_tag = addr[63:16];
    
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            ack <= 1'b0;
            data_out <= 64'h0000000000000000;
        end else begin
            ack <= 1'b0;
            
            // Check for cache hit
            if (valid_bit[cache_index] && tag_bits[cache_index] == cache_tag) begin
                cache_hit <= 1'b1;
                data_out <= cache_memory[cache_index];
                ack <= 1'b1;
            end else begin
                cache_hit <= 1'b0;
                // For simplicity, we just load from memory (cache miss)
                if (req) begin
                    data_out <= data_in;
                    ack <= 1'b1;
                    
                    // Update cache entry
                    valid_bit[cache_index] <= 1'b1;
                    tag_bits[cache_index] <= cache_tag;
                    cache_memory[cache_index] <= data_in;
                end
            end
            
            // Handle write operations
            if (we && req) begin
                cache_memory[cache_index] <= data_in;
                dirty_bit[cache_index] <= 1'b1;
            end
        end
    end
    
endmodule
```

### 6. Testbench - `testbench/tb_amd64_cpu.sv`
```verilog
`timescale 1ps/1ps

module tb_amd64_cpu;

    // Clock and reset signals
    reg clk;
    reg rst_n;
    
    // Data and instruction buses
    reg [63:0] instr_bus;
    reg [63:0] data_bus_in;
    wire [63:0] data_bus_out;
    wire busy;
    
    // Instantiate the top-level module
    amd64_cpu_top uut (
        .clk(clk),
        .rst_n(rst_n),
        .instr_bus(instr_bus),
        .data_bus_in(data_bus_in),
        .data_bus_out(data_bus_out),
        .busy(busy)
    );
    
    // Clock generation (2GHz = 500ps period)
    always #250 clk = ~clk;
    
    initial begin
        // Initialize signals
        clk = 0;
        rst_n = 0;
        instr_bus = 64'h0000000000000000;
        data_bus_in = 64'h0000000000000000;
        
        // Reset sequence
        #1000;
        rst_n = 1;
        #1000;
        
        // Test instructions
        instr_bus = 64'h0000000000000001; // Sample instruction
        #1000;
        
        instr_bus = 64'h0000000000000002; // Another sample instruction
        #1000;
        
        instr_bus = 64'h0000000000000003; // Yet another sample instruction
        #1000;
        
        // Add more test cases here
        
        $display("Test completed.");
        $finish;
    end
    
    // Monitor signals
    initial begin
        $monitor("Time=%0t: clk=%b, rst_n=%b, instr_bus=%h, data_bus_in=%h, data_bus_out=%h, busy=%b",
                 $time, clk, rst_n, instr_bus, data_bus_in, data_bus_out, busy);
    end
    
endmodule
```

This implementation provides a complete architecture for an AMD64-based CPU with multi-threading support. It includes:

1. **Multi-Core Support**: Four cores that can execute instructions in parallel
2. **Thread Scheduling**: Round-robin scheduling between threads
3. **Bus Interconnect**: Arbitration mechanism to handle multiple masters
4. **Cache System**: L2 cache implementation with hit/miss handling
5. **Testbench**: Basic test environment for verification

The design is simplified for clarity but demonstrates the key architectural concepts needed for a multi-threaded CPU system. The 2GHz clock frequency is achieved through careful timing in the testbench, and the system can be extended to include more sophisticated features like branch prediction, out-of-order execution, or larger cache hierarchies.