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gabrielosh |
////////////////////////////////////////////////////////////////////////////
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//// ////
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//// T6507LP IP Core ////
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//// ////
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//// This file is part of the T6507LP project ////
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//// http://www.opencores.org/cores/t6507lp/ ////
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//// ////
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//// Description ////
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//// 6507 FSM ////
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//// ////
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//// TODO: ////
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//// - Fix relative mode, bit 7 means negative ////
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//// - Check reset behavior ////
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//// - Comment the code ////
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//// ////
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//// Author(s): ////
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//// - Gabriel Oshiro Zardo, gabrieloshiro@gmail.com ////
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//// - Samuel Nascimento Pagliarini (creep), snpagliarini@gmail.com ////
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//// ////
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////////////////////////////////////////////////////////////////////////////
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//// ////
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//// Copyright (C) 2001 Authors and OPENCORES.ORG ////
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//// ////
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//// This source file may be used and distributed without ////
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//// restriction provided that this copyright statement is not ////
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//// removed from the file and that any derivative work contains ////
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//// the original copyright notice and the associated disclaimer. ////
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//// ////
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//// This source file is free software; you can redistribute it ////
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//// and/or modify it under the terms of the GNU Lesser General ////
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//// Public License as published by the Free Software Foundation; ////
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//// either version 2.1 of the License, or (at your option) any ////
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//// later version. ////
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//// ////
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//// This source is distributed in the hope that it will be ////
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//// useful, but WITHOUT ANY WARRANTY; without even the implied ////
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//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR ////
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//// PURPOSE. See the GNU Lesser General Public License for more ////
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//// details. ////
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//// ////
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//// You should have received a copy of the GNU Lesser General ////
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//// Public License along with this source; if not, download it ////
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//// from http://www.opencores.org/lgpl.shtml ////
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//// ////
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////////////////////////////////////////////////////////////////////////////
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`include "timescale.v"
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module t6507lp_fsm(clk, reset_n, alu_result, alu_status, data_in, alu_x, alu_y, address, mem_rw, data_out, alu_opcode, alu_a, alu_enable);
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parameter [3:0] DATA_SIZE = 4'd8;
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parameter [3:0] ADDR_SIZE = 4'd13;
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localparam [3:0] DATA_SIZE_ = DATA_SIZE - 4'b0001;
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localparam [3:0] ADDR_SIZE_ = ADDR_SIZE - 4'b0001;
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input clk; // master clock
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input reset_n; // active low reset
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input [DATA_SIZE_:0] alu_result; // result from alu operation
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input [DATA_SIZE_:0] alu_status; // alu status register
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input [DATA_SIZE_:0] data_in; // data that comes from the bus controller
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input [DATA_SIZE_:0] alu_x; // alu x index register
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input [DATA_SIZE_:0] alu_y; // alu y index register
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output reg [ADDR_SIZE_:0] address; // system bus address
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output reg mem_rw; // read = 0, write = 1
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output reg [DATA_SIZE_:0] data_out; // data that will be written somewhere else
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output reg [DATA_SIZE_:0] alu_opcode; // current opcode
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output reg [DATA_SIZE_:0] alu_a; // extra operand sent to the alu
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output reg alu_enable; // a flag that when high tells the alu when to perform the operations
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// FSM states. If aiming for less power consumption try gray coding.
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//localparam FETCH_OP_CALC = 5'b00001; this was never used
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localparam FETCH_OP = 5'b00000;
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localparam FETCH_LOW = 5'b00010;
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localparam FETCH_HIGH = 5'b00011;
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localparam READ_MEM = 5'b00100;
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localparam DUMMY_WRT_CALC = 5'b00101;
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localparam WRITE_MEM = 5'b00110;
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localparam FETCH_OP_CALC_PARAM = 5'b00111;
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localparam READ_MEM_CALC_INDEX = 5'b01000;
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localparam FETCH_HIGH_CALC_INDEX = 5'b01001;
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localparam READ_MEM_FIX_ADDR = 5'b01010;
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localparam FETCH_OP_EVAL_BRANCH = 5'b01011;
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localparam FETCH_OP_FIX_PC = 5'b01100;
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localparam READ_FROM_POINTER = 5'b01101;
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localparam READ_FROM_POINTER_X = 5'b01110;
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localparam READ_FROM_POINTER_X1 = 5'b01111;
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localparam PUSH_PCH = 5'b10000;
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localparam PUSH_PCL = 5'b10001;
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localparam PUSH_STATUS = 5'b10010;
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localparam FETCH_PCL = 5'b10011;
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localparam FETCH_PCH = 5'b10100;
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localparam INCREMENT_SP = 5'b10101;
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localparam PULL_STATUS = 5'b10110;
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localparam PULL_PCL = 5'b10111;
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localparam PULL_PCH = 5'b11000;
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localparam INCREMENT_PC = 5'b11001;
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localparam PUSH_REGISTER = 5'b11010;
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localparam PULL_REGISTER = 5'b11011;
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localparam DUMMY = 5'b11100;
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localparam RESET = 5'b11111;
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// OPCODES TODO: verify how this get synthesised
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146 |
creep |
`include "t6507lp_package.v"
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128 |
gabrielosh |
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// mem_rw signals
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localparam MEM_READ = 1'b0;
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localparam MEM_WRITE = 1'b1;
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reg [ADDR_SIZE_:0] pc; // program counter
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reg [DATA_SIZE:0] sp; // stack pointer. 9 bits wide.
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reg [DATA_SIZE_:0] ir; // instruction register
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reg [ADDR_SIZE_:0] temp_addr; // temporary address
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reg [DATA_SIZE_:0] temp_data; // temporary data
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reg [4:0] state, next_state; // current and next state registers
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// wiring that simplifies the FSM logic by simplifying the addressing modes
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reg absolute;
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reg absolute_indexed;
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reg accumulator;
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reg immediate;
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reg implied;
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reg indirectx;
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reg indirecty;
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reg relative;
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reg zero_page;
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reg zero_page_indexed;
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reg [DATA_SIZE_:0] index; // will be assigned with either X or Y
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// regs that store the type of operation. again, this simplifies the FSM a lot.
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reg read;
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reg read_modify_write;
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reg write;
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reg jump;
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reg jump_indirect;
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// regs for the special instructions
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reg brk;
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reg rti;
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reg rts;
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reg pha;
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reg php;
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reg pla;
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reg plp;
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194 |
creep |
reg jsr;
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reg tsx;
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205 |
creep |
reg txs;
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reg nop;
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128 |
gabrielosh |
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wire [ADDR_SIZE_:0] next_pc; // a simple logic to add one to the PC
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assign next_pc = pc + 13'b0000000000001;
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200 |
creep |
wire [DATA_SIZE:0] sp_plus_one; // simple adder and subtracter for the stack pointer
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assign sp_plus_one = {1'b1, sp[7:0] + 8'b000000001};
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128 |
gabrielosh |
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200 |
creep |
wire [DATA_SIZE:0] sp_minus_one;
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assign sp_minus_one = {1'b1, sp[7:0] - 8'b000000001};
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128 |
gabrielosh |
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reg [ADDR_SIZE_:0] address_plus_index; // this two registers are used when the instruction uses indexing.
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reg page_crossed; // address_plus_index always adds index to address and page_crossed asserts when the sum creates a carry.
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reg branch; // a simple reg that is asserted everytime a branch will be executed.
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// this is the combinational logic related to indexed instructions
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always @(*) begin
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200 |
creep |
address_plus_index = 13'h000;
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128 |
gabrielosh |
page_crossed = 1'b0;
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200 |
creep |
if ( (state == READ_MEM_CALC_INDEX) || (state == READ_MEM_FIX_ADDR) || (state == FETCH_HIGH_CALC_INDEX) ) begin
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128 |
gabrielosh |
{page_crossed, address_plus_index[7:0]} = temp_addr[7:0] + index;
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address_plus_index[12:8] = temp_addr[12:8] + page_crossed;
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end
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else if (branch) begin
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if (state == FETCH_OP_FIX_PC || state == FETCH_OP_EVAL_BRANCH) begin
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{page_crossed, address_plus_index[7:0]} = pc[7:0] + index;
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address_plus_index[12:8] = pc[12:8] + page_crossed; // warning: pc might feed these lines twice and cause branch failure
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end // solution: add a temp reg i guess
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end
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else if (state == READ_FROM_POINTER) begin
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if (indirectx) begin
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{page_crossed, address_plus_index[7:0]} = temp_data + index;
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address_plus_index[12:8] = 5'b00000;
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end
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else if (jump_indirect) begin
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200 |
creep |
address_plus_index[7:0] = temp_addr[7:0] + 8'h01;
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128 |
gabrielosh |
address_plus_index[12:8] = 5'b00000;
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end
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else begin // indirecty falls here
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address_plus_index[7:0] = temp_data + 8'h01;
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address_plus_index[12:8] = 5'b00000;
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end
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end
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else if (state == READ_FROM_POINTER_X) begin
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{page_crossed, address_plus_index[7:0]} = temp_data + index + 8'h01;
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address_plus_index[12:8] = 5'b00000;
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end
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else if (state == READ_FROM_POINTER_X1) begin
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{page_crossed, address_plus_index[7:0]} = temp_addr[7:0] + index;
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address_plus_index[12:8] = temp_addr[12:8] + page_crossed;
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end
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end
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146 |
creep |
reg [2:0] rst_counter; // a counter to preserve the cpu idle for six cycles
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128 |
gabrielosh |
always @ (posedge clk or negedge reset_n) begin // sequencial always block
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if (reset_n == 1'b0) begin
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// all registers must assume default values
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200 |
creep |
pc <= 13'h0; // TODO: this is written somewhere. something about a reset vector. must be checked.
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194 |
creep |
sp <= 9'b111111111; // the default is 'h1FF
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128 |
gabrielosh |
ir <= 8'h00;
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temp_addr <= 13'h0000;
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temp_data <= 8'h00;
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state <= RESET;
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// registered outputs also receive default values
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address <= 13'h0000;
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mem_rw <= MEM_READ;
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data_out <= 8'h00;
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200 |
creep |
rst_counter <= 3'h0;
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128 |
gabrielosh |
end
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else begin
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state <= next_state;
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146 |
creep |
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128 |
gabrielosh |
case (state)
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RESET: begin // The processor was reset
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| 226 |
200 |
creep |
rst_counter <= rst_counter + 3'b001;
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| 227 |
194 |
creep |
//sp <= 9'b111111111; // this prevents flipflops with different drivers
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| 228 |
128 |
gabrielosh |
//$write("under reset");
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| 229 |
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end
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/*
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FETCH_OP: executed when the processor was reset or the last instruction could not fetch.
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FETCH_OP_CALC_PARAM: enables the alu with an argument (alu_a) and fetchs the next instruction opcode. (pipelining)
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*/
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FETCH_OP, FETCH_OP_CALC_PARAM: begin // this is the pipeline happening!
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pc <= next_pc;
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address <= next_pc;
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mem_rw <= MEM_READ;
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ir <= data_in;
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end
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/*
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| 241 |
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in this state the opcode is already known so truly execution begins.
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| 242 |
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all instructions execute this cycle.
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| 243 |
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*/
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| 244 |
196 |
creep |
FETCH_LOW: begin
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| 245 |
195 |
creep |
if (accumulator || implied || txs || tsx) begin
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| 246 |
128 |
gabrielosh |
pc <= pc; // is this better?
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| 247 |
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address <= pc;
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| 248 |
194 |
creep |
mem_rw <= MEM_READ;
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| 249 |
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if (txs) begin
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| 251 |
196 |
creep |
sp[7:0] <= alu_x;
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| 252 |
194 |
creep |
end
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| 253 |
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//alu_a
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| 254 |
128 |
gabrielosh |
end
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| 255 |
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else if (immediate || relative) begin
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| 256 |
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pc <= next_pc;
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| 257 |
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address <= next_pc;
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| 258 |
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mem_rw <= MEM_READ;
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| 259 |
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temp_data <= data_in; // the follow-up byte is saved in temp_data
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| 260 |
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end
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| 261 |
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else if (absolute || absolute_indexed || jump_indirect) begin
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| 262 |
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pc <= next_pc;
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| 263 |
196 |
creep |
address <= next_pc;
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| 264 |
128 |
gabrielosh |
mem_rw <= MEM_READ;
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| 265 |
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temp_addr <= {{5{1'b0}},data_in};
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| 266 |
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temp_data <= 8'h00;
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| 267 |
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end
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| 268 |
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else if (zero_page) begin
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| 269 |
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pc <= next_pc;
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| 270 |
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address <= {{5{1'b0}},data_in};
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| 271 |
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temp_addr <= {{5{1'b0}},data_in};
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| 272 |
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| 273 |
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if (write) begin
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| 274 |
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mem_rw <= MEM_WRITE;
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| 275 |
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data_out <= alu_result;
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| 276 |
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end
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| 277 |
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else begin
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| 278 |
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mem_rw <= MEM_READ;
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| 279 |
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data_out <= 8'h00;
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| 280 |
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end
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| 281 |
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end
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| 282 |
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else if (zero_page_indexed) begin
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| 283 |
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pc <= next_pc;
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| 284 |
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address <= {{5{1'b0}}, data_in};
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| 285 |
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temp_addr <= {{5{1'b0}}, data_in};
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| 286 |
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mem_rw <= MEM_READ;
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| 287 |
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end
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| 288 |
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else if (indirectx || indirecty) begin
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| 289 |
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pc <= next_pc;
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| 290 |
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address <= data_in;
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| 291 |
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temp_data <= data_in;
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| 292 |
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mem_rw <= MEM_READ;
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| 293 |
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end
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| 294 |
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else begin // the special instructions will fall here: BRK, RTI, RTS...
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| 295 |
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if (brk) begin
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| 296 |
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pc <= next_pc;
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| 297 |
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address <= sp;
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| 298 |
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data_out <= {{3{1'b0}}, pc[12:8]};
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| 299 |
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mem_rw <= MEM_WRITE;
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| 300 |
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end
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| 301 |
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else if (rti || rts) begin
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| 302 |
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address <= sp;
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| 303 |
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mem_rw <= MEM_READ;
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| 304 |
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end
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| 305 |
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else if (pha || php) begin
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| 306 |
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pc <= pc;
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| 307 |
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address <= sp;
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| 308 |
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data_out <= (pha) ? alu_result : alu_status;
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| 309 |
|
|
mem_rw <= MEM_WRITE;
|
| 310 |
|
|
end
|
| 311 |
|
|
else if (pla || plp) begin
|
| 312 |
|
|
pc <= pc;
|
| 313 |
|
|
address <= sp;
|
| 314 |
|
|
mem_rw <= MEM_READ;
|
| 315 |
|
|
end
|
| 316 |
|
|
else begin // jsr
|
| 317 |
|
|
address <= sp;
|
| 318 |
|
|
mem_rw <= MEM_READ;
|
| 319 |
|
|
temp_addr <= {{5{1'b0}}, data_in};
|
| 320 |
|
|
pc <= next_pc;
|
| 321 |
|
|
end
|
| 322 |
|
|
end
|
| 323 |
|
|
end
|
| 324 |
|
|
FETCH_HIGH_CALC_INDEX: begin
|
| 325 |
|
|
pc <= next_pc;
|
| 326 |
|
|
temp_addr[12:8] <= data_in[4:0];
|
| 327 |
|
|
address <= {data_in[4:0], address_plus_index[7:0]};
|
| 328 |
|
|
mem_rw <= MEM_READ;
|
| 329 |
|
|
data_out <= 8'h00;
|
| 330 |
|
|
end
|
| 331 |
|
|
// this cycle fetchs the next operand while still evaluating if a branch occurred.
|
| 332 |
|
|
FETCH_OP_EVAL_BRANCH: begin
|
| 333 |
|
|
if (branch) begin
|
| 334 |
|
|
pc <= {{5{1'b0}}, address_plus_index[7:0]};
|
| 335 |
|
|
address <= {{5{1'b0}}, address_plus_index[7:0]};
|
| 336 |
|
|
mem_rw <= MEM_READ;
|
| 337 |
|
|
data_out <= 8'h00;
|
| 338 |
|
|
end
|
| 339 |
|
|
else begin
|
| 340 |
|
|
pc <= next_pc;
|
| 341 |
|
|
address <= next_pc;
|
| 342 |
|
|
mem_rw <= MEM_READ;
|
| 343 |
|
|
data_out <= 8'h00;
|
| 344 |
|
|
ir <= data_in;
|
| 345 |
|
|
end
|
| 346 |
|
|
end
|
| 347 |
|
|
// sometimes when reading memory page crosses may occur. the pc register must be fixed, i.e., add 16'h0100
|
| 348 |
|
|
FETCH_OP_FIX_PC: begin
|
| 349 |
|
|
if (page_crossed) begin
|
| 350 |
|
|
pc[12:8] <= address_plus_index[12:8];
|
| 351 |
|
|
address[12:8] <= address_plus_index[12:8];
|
| 352 |
|
|
end
|
| 353 |
|
|
else begin
|
| 354 |
|
|
pc <= next_pc;
|
| 355 |
|
|
address <= next_pc;
|
| 356 |
|
|
mem_rw <= MEM_READ;
|
| 357 |
|
|
ir <= data_in;
|
| 358 |
|
|
end
|
| 359 |
|
|
end
|
| 360 |
|
|
// several instructions ocupy 3 bytes in memory. this cycle reads the third byte.
|
| 361 |
|
|
FETCH_HIGH: begin
|
| 362 |
|
|
if (jump) begin
|
| 363 |
|
|
pc <= {data_in[4:0], temp_addr[7:0]}; // PCL <= first byte, PCH <= second byte
|
| 364 |
|
|
address <= {data_in[4:0], temp_addr[7:0]};
|
| 365 |
|
|
mem_rw <= MEM_READ;
|
| 366 |
|
|
data_out <= 8'h00;
|
| 367 |
|
|
end
|
| 368 |
|
|
else begin
|
| 369 |
|
|
if (write) begin
|
| 370 |
|
|
pc <= next_pc;
|
| 371 |
|
|
temp_addr[12:8] <= data_in[4:0];
|
| 372 |
|
|
address <= {data_in[4:0],temp_addr[7:0]};
|
| 373 |
|
|
mem_rw <= MEM_WRITE;
|
| 374 |
|
|
data_out <= alu_result;
|
| 375 |
|
|
end
|
| 376 |
|
|
else begin // read_modify_write or just read
|
| 377 |
|
|
pc <= next_pc;
|
| 378 |
|
|
temp_addr[12:8] <= data_in[4:0];
|
| 379 |
|
|
address <= {data_in[4:0],temp_addr[7:0]};
|
| 380 |
|
|
mem_rw <= MEM_READ;
|
| 381 |
|
|
data_out <= 8'h00;
|
| 382 |
|
|
end
|
| 383 |
|
|
end
|
| 384 |
|
|
end
|
| 385 |
|
|
// read memory at address
|
| 386 |
|
|
READ_MEM: begin
|
| 387 |
|
|
if (read_modify_write) begin
|
| 388 |
|
|
pc <= pc;
|
| 389 |
|
|
address <= temp_addr;
|
| 390 |
|
|
mem_rw <= MEM_WRITE;
|
| 391 |
|
|
temp_data <= data_in;
|
| 392 |
|
|
data_out <= data_in; // writeback the same value
|
| 393 |
|
|
end
|
| 394 |
|
|
else begin
|
| 395 |
|
|
pc <= pc;
|
| 396 |
|
|
address <= pc;
|
| 397 |
|
|
temp_data <= data_in;
|
| 398 |
|
|
mem_rw <= MEM_READ;
|
| 399 |
|
|
data_out <= 8'h00;
|
| 400 |
|
|
end
|
| 401 |
|
|
end
|
| 402 |
|
|
READ_MEM_CALC_INDEX: begin
|
| 403 |
|
|
address <= address_plus_index;
|
| 404 |
|
|
temp_addr <= address_plus_index;
|
| 405 |
|
|
|
| 406 |
|
|
if (write) begin
|
| 407 |
|
|
mem_rw <= MEM_WRITE;
|
| 408 |
|
|
data_out <= alu_result;
|
| 409 |
|
|
end
|
| 410 |
|
|
else begin
|
| 411 |
|
|
mem_rw <= MEM_READ;
|
| 412 |
|
|
data_out <= 8'h00;
|
| 413 |
|
|
end
|
| 414 |
|
|
|
| 415 |
|
|
end
|
| 416 |
|
|
READ_MEM_FIX_ADDR: begin
|
| 417 |
|
|
if (read) begin
|
| 418 |
|
|
mem_rw <= MEM_READ;
|
| 419 |
|
|
data_out <= 8'h00;
|
| 420 |
|
|
|
| 421 |
|
|
if (page_crossed) begin // fix address
|
| 422 |
|
|
address <= address_plus_index;
|
| 423 |
|
|
temp_addr <= address_plus_index;
|
| 424 |
|
|
end
|
| 425 |
|
|
else begin
|
| 426 |
|
|
address <= pc;
|
| 427 |
|
|
temp_data <= data_in;
|
| 428 |
|
|
end
|
| 429 |
|
|
end
|
| 430 |
|
|
else if (write) begin
|
| 431 |
|
|
mem_rw <= MEM_WRITE;
|
| 432 |
|
|
data_out <= alu_result;
|
| 433 |
|
|
address <= address_plus_index;
|
| 434 |
|
|
temp_addr <= address_plus_index;
|
| 435 |
|
|
|
| 436 |
|
|
end
|
| 437 |
|
|
else begin // read modify write
|
| 438 |
|
|
mem_rw <= MEM_READ;
|
| 439 |
|
|
data_out <= 8'h00;
|
| 440 |
|
|
address <= address_plus_index;
|
| 441 |
|
|
temp_addr <= address_plus_index;
|
| 442 |
|
|
end
|
| 443 |
|
|
end
|
| 444 |
|
|
// some instructions have a dummy write cycle. this is it.
|
| 445 |
|
|
DUMMY_WRT_CALC: begin
|
| 446 |
|
|
pc <= pc;
|
| 447 |
|
|
address <= temp_addr;
|
| 448 |
|
|
mem_rw <= MEM_WRITE;
|
| 449 |
|
|
data_out <= alu_result;
|
| 450 |
|
|
end
|
| 451 |
|
|
WRITE_MEM: begin
|
| 452 |
|
|
pc <= pc;
|
| 453 |
|
|
address <= pc;
|
| 454 |
|
|
mem_rw <= MEM_READ;
|
| 455 |
|
|
data_out <= 8'h00;
|
| 456 |
|
|
end
|
| 457 |
|
|
READ_FROM_POINTER: begin
|
| 458 |
|
|
if (jump_indirect) begin
|
| 459 |
|
|
pc[7:0] <= data_in;
|
| 460 |
|
|
mem_rw <= MEM_READ;
|
| 461 |
|
|
address <= address_plus_index;
|
| 462 |
|
|
end
|
| 463 |
|
|
else begin
|
| 464 |
|
|
pc <= pc;
|
| 465 |
|
|
mem_rw <= MEM_READ;
|
| 466 |
|
|
|
| 467 |
|
|
if (indirectx) begin
|
| 468 |
|
|
address <= address_plus_index;
|
| 469 |
|
|
end
|
| 470 |
|
|
else begin // indirecty falls here
|
| 471 |
|
|
address <= address_plus_index;
|
| 472 |
|
|
temp_addr <= {{5{1'b0}}, data_in};
|
| 473 |
|
|
end
|
| 474 |
|
|
end
|
| 475 |
|
|
end
|
| 476 |
|
|
READ_FROM_POINTER_X: begin
|
| 477 |
|
|
pc <= pc;
|
| 478 |
|
|
address <= address_plus_index;
|
| 479 |
|
|
temp_addr[7:0] <= data_in;
|
| 480 |
|
|
mem_rw <= MEM_READ;
|
| 481 |
|
|
end
|
| 482 |
|
|
READ_FROM_POINTER_X1: begin
|
| 483 |
|
|
if (jump_indirect) begin
|
| 484 |
|
|
pc[12:8] <= data_in[4:0];
|
| 485 |
|
|
mem_rw <= MEM_READ;
|
| 486 |
|
|
address <= {data_in[4:0], pc[7:0]};
|
| 487 |
|
|
end
|
| 488 |
|
|
else if (indirectx) begin
|
| 489 |
|
|
address <= {data_in[4:0], temp_addr[7:0]};
|
| 490 |
|
|
if (write) begin
|
| 491 |
|
|
mem_rw <= MEM_WRITE;
|
| 492 |
|
|
data_out <= alu_result;
|
| 493 |
|
|
end
|
| 494 |
|
|
else begin
|
| 495 |
|
|
mem_rw <= MEM_READ;
|
| 496 |
|
|
end
|
| 497 |
|
|
end
|
| 498 |
|
|
else begin // indirecty falls here
|
| 499 |
|
|
address <= address_plus_index;
|
| 500 |
|
|
temp_addr[12:8] <= data_in;
|
| 501 |
|
|
mem_rw <= MEM_READ;
|
| 502 |
|
|
end
|
| 503 |
|
|
end
|
| 504 |
|
|
PUSH_PCH: begin
|
| 505 |
|
|
pc <= pc;
|
| 506 |
|
|
address <= sp_minus_one;
|
| 507 |
|
|
data_out <= pc[7:0];
|
| 508 |
|
|
mem_rw <= MEM_WRITE;
|
| 509 |
|
|
sp <= sp_minus_one;
|
| 510 |
|
|
end
|
| 511 |
|
|
PUSH_PCL: begin
|
| 512 |
|
|
if (jsr) begin
|
| 513 |
|
|
pc <= pc;
|
| 514 |
|
|
address <= pc;
|
| 515 |
|
|
mem_rw <= MEM_READ;
|
| 516 |
|
|
sp <= sp_minus_one;
|
| 517 |
|
|
end
|
| 518 |
|
|
else begin
|
| 519 |
|
|
pc <= pc;
|
| 520 |
|
|
address <= sp_minus_one;
|
| 521 |
|
|
data_out <= alu_status;
|
| 522 |
|
|
mem_rw <= MEM_WRITE;
|
| 523 |
|
|
sp <= sp_minus_one;
|
| 524 |
|
|
end
|
| 525 |
|
|
end
|
| 526 |
|
|
PUSH_STATUS: begin
|
| 527 |
199 |
creep |
address <= 13'h1FFE;
|
| 528 |
128 |
gabrielosh |
mem_rw <= MEM_READ;
|
| 529 |
196 |
creep |
sp <= sp_minus_one;
|
| 530 |
128 |
gabrielosh |
end
|
| 531 |
|
|
FETCH_PCL: begin
|
| 532 |
|
|
pc[7:0] <= data_in;
|
| 533 |
199 |
creep |
address <= 13'h1FFF;
|
| 534 |
128 |
gabrielosh |
mem_rw <= MEM_READ;
|
| 535 |
|
|
end
|
| 536 |
|
|
FETCH_PCH: begin
|
| 537 |
|
|
pc[12:8] <= data_in[4:0];
|
| 538 |
|
|
address <= {data_in[4:0], pc[7:0]};
|
| 539 |
|
|
mem_rw <= MEM_READ;
|
| 540 |
|
|
end
|
| 541 |
|
|
INCREMENT_SP: begin
|
| 542 |
|
|
sp <= sp_plus_one;
|
| 543 |
|
|
address <= sp_plus_one;
|
| 544 |
|
|
end
|
| 545 |
|
|
PULL_STATUS: begin
|
| 546 |
|
|
sp <= sp_plus_one;
|
| 547 |
|
|
address <= sp_plus_one;
|
| 548 |
|
|
temp_data <= data_in;
|
| 549 |
|
|
end
|
| 550 |
|
|
PULL_PCL: begin
|
| 551 |
|
|
sp <= sp_plus_one;
|
| 552 |
|
|
address <= sp_plus_one;
|
| 553 |
|
|
pc[7:0] <= data_in;
|
| 554 |
|
|
end
|
| 555 |
|
|
PULL_PCH: begin
|
| 556 |
|
|
pc[12:8] <= data_in[4:0];
|
| 557 |
|
|
address <= {data_in[4:0], pc[7:0]};
|
| 558 |
|
|
end
|
| 559 |
|
|
INCREMENT_PC: begin
|
| 560 |
|
|
pc <= next_pc;
|
| 561 |
|
|
address <= next_pc;
|
| 562 |
|
|
end
|
| 563 |
|
|
PUSH_REGISTER: begin
|
| 564 |
|
|
pc <= pc;
|
| 565 |
|
|
address <= pc;
|
| 566 |
|
|
sp <= sp_minus_one;
|
| 567 |
|
|
mem_rw <= MEM_READ;
|
| 568 |
|
|
temp_data <= data_in;
|
| 569 |
|
|
end
|
| 570 |
|
|
PULL_REGISTER: begin
|
| 571 |
|
|
pc <= pc;
|
| 572 |
|
|
address <= pc;
|
| 573 |
|
|
temp_data <= data_in;
|
| 574 |
|
|
end
|
| 575 |
|
|
DUMMY: begin
|
| 576 |
|
|
address <= sp;
|
| 577 |
|
|
mem_rw <= MEM_WRITE;
|
| 578 |
|
|
end
|
| 579 |
|
|
default: begin
|
| 580 |
|
|
//$write("unknown state"); // TODO: check if synth really ignores this 2 lines. Otherwise wrap it with a `ifdef
|
| 581 |
|
|
//$finish(0);
|
| 582 |
|
|
end
|
| 583 |
|
|
|
| 584 |
|
|
endcase
|
| 585 |
|
|
end
|
| 586 |
|
|
end
|
| 587 |
|
|
|
| 588 |
|
|
always @ (*) begin // this is the next_state logic and the combinational output logic always block
|
| 589 |
|
|
alu_opcode = 8'h00;
|
| 590 |
|
|
alu_a = 8'h00;
|
| 591 |
|
|
alu_enable = 1'b0;
|
| 592 |
|
|
next_state = RESET; // these lines prevents latches
|
| 593 |
|
|
|
| 594 |
|
|
case (state)
|
| 595 |
|
|
RESET: begin
|
| 596 |
200 |
creep |
if (rst_counter == 3'd6) begin
|
| 597 |
146 |
creep |
next_state = FETCH_OP;
|
| 598 |
|
|
end
|
| 599 |
128 |
gabrielosh |
end
|
| 600 |
|
|
FETCH_OP: begin
|
| 601 |
|
|
next_state = FETCH_LOW;
|
| 602 |
|
|
end
|
| 603 |
|
|
FETCH_OP_CALC_PARAM: begin
|
| 604 |
|
|
next_state = FETCH_LOW;
|
| 605 |
|
|
alu_opcode = ir;
|
| 606 |
|
|
alu_enable = 1'b1;
|
| 607 |
|
|
alu_a = temp_data;
|
| 608 |
|
|
end
|
| 609 |
|
|
FETCH_LOW: begin
|
| 610 |
195 |
creep |
if (accumulator || implied || txs) begin
|
| 611 |
205 |
creep |
if (!nop) begin
|
| 612 |
|
|
alu_opcode = ir;
|
| 613 |
|
|
alu_enable = 1'b1;
|
| 614 |
|
|
end
|
| 615 |
194 |
creep |
next_state = FETCH_OP;
|
| 616 |
128 |
gabrielosh |
end
|
| 617 |
195 |
creep |
else if (tsx) begin
|
| 618 |
|
|
alu_opcode = ir;
|
| 619 |
|
|
alu_enable = 1'b1;
|
| 620 |
|
|
next_state = FETCH_OP;
|
| 621 |
|
|
alu_a = sp[7:0];
|
| 622 |
|
|
end
|
| 623 |
128 |
gabrielosh |
else if (immediate) begin
|
| 624 |
|
|
next_state = FETCH_OP_CALC_PARAM;
|
| 625 |
|
|
end
|
| 626 |
|
|
else if (zero_page) begin
|
| 627 |
|
|
if (read || read_modify_write) begin
|
| 628 |
|
|
next_state = READ_MEM;
|
| 629 |
|
|
end
|
| 630 |
|
|
else if (write) begin
|
| 631 |
|
|
next_state = WRITE_MEM;
|
| 632 |
|
|
alu_opcode = ir;
|
| 633 |
|
|
alu_enable = 1'b1;
|
| 634 |
|
|
alu_a = 8'h00;
|
| 635 |
|
|
end
|
| 636 |
|
|
else begin
|
| 637 |
|
|
//$write("unknown behavior");
|
| 638 |
|
|
//$finish(0);
|
| 639 |
|
|
end
|
| 640 |
|
|
end
|
| 641 |
|
|
else if (zero_page_indexed) begin
|
| 642 |
|
|
next_state = READ_MEM_CALC_INDEX;
|
| 643 |
|
|
end
|
| 644 |
|
|
else if (absolute || jump_indirect) begin
|
| 645 |
|
|
next_state = FETCH_HIGH;
|
| 646 |
|
|
if (write) begin // this is being done one cycle early but i have checked and the ALU will still work properly
|
| 647 |
|
|
alu_opcode = ir;
|
| 648 |
|
|
alu_enable = 1'b1;
|
| 649 |
|
|
alu_a = 8'h00;
|
| 650 |
|
|
end
|
| 651 |
|
|
end
|
| 652 |
|
|
else if (absolute_indexed) begin
|
| 653 |
|
|
next_state = FETCH_HIGH_CALC_INDEX;
|
| 654 |
|
|
end
|
| 655 |
|
|
else if (relative) begin
|
| 656 |
|
|
next_state = FETCH_OP_EVAL_BRANCH;
|
| 657 |
|
|
end
|
| 658 |
|
|
else if (indirectx || indirecty) begin
|
| 659 |
|
|
next_state = READ_FROM_POINTER;
|
| 660 |
|
|
end
|
| 661 |
|
|
else begin // all the special instructions will fall here
|
| 662 |
|
|
if (brk) begin
|
| 663 |
|
|
next_state = PUSH_PCH;
|
| 664 |
|
|
end
|
| 665 |
|
|
else if (rti || rts) begin
|
| 666 |
|
|
next_state = INCREMENT_SP;
|
| 667 |
|
|
end
|
| 668 |
|
|
else if (pha) begin
|
| 669 |
|
|
alu_opcode = ir;
|
| 670 |
|
|
alu_enable = 1'b1;
|
| 671 |
|
|
//alu_a = 8'h00;
|
| 672 |
|
|
next_state = PUSH_REGISTER;
|
| 673 |
|
|
end
|
| 674 |
|
|
else if (php) begin
|
| 675 |
|
|
next_state = PUSH_REGISTER;
|
| 676 |
|
|
end
|
| 677 |
|
|
else if (pla || plp) begin
|
| 678 |
|
|
next_state = INCREMENT_SP;
|
| 679 |
|
|
end
|
| 680 |
|
|
else begin // jsr
|
| 681 |
|
|
next_state = DUMMY;
|
| 682 |
|
|
end
|
| 683 |
|
|
end
|
| 684 |
|
|
end
|
| 685 |
|
|
READ_FROM_POINTER: begin
|
| 686 |
|
|
if (indirectx) begin
|
| 687 |
|
|
next_state = READ_FROM_POINTER_X;
|
| 688 |
|
|
end
|
| 689 |
|
|
else begin // indirecty and jump indirect falls here
|
| 690 |
|
|
next_state = READ_FROM_POINTER_X1;
|
| 691 |
|
|
end
|
| 692 |
|
|
end
|
| 693 |
|
|
READ_FROM_POINTER_X: begin
|
| 694 |
|
|
next_state = READ_FROM_POINTER_X1;
|
| 695 |
|
|
end
|
| 696 |
|
|
READ_FROM_POINTER_X1: begin
|
| 697 |
|
|
if (jump_indirect) begin
|
| 698 |
|
|
next_state = FETCH_OP;
|
| 699 |
|
|
end
|
| 700 |
|
|
else if (indirecty) begin
|
| 701 |
|
|
next_state = READ_MEM_FIX_ADDR;
|
| 702 |
|
|
end
|
| 703 |
|
|
else begin
|
| 704 |
|
|
if (read) begin // no instruction using pointers is from type read_modify_write
|
| 705 |
|
|
next_state = READ_MEM;
|
| 706 |
|
|
end
|
| 707 |
|
|
else if (write) begin
|
| 708 |
|
|
alu_opcode = ir;
|
| 709 |
|
|
alu_enable = 1'b1;
|
| 710 |
|
|
next_state = WRITE_MEM;
|
| 711 |
|
|
end
|
| 712 |
|
|
end
|
| 713 |
|
|
end
|
| 714 |
|
|
FETCH_OP_EVAL_BRANCH: begin
|
| 715 |
|
|
if (branch) begin
|
| 716 |
|
|
next_state = FETCH_OP_FIX_PC;
|
| 717 |
|
|
end
|
| 718 |
|
|
else begin
|
| 719 |
|
|
next_state = FETCH_LOW;
|
| 720 |
|
|
end
|
| 721 |
|
|
end
|
| 722 |
|
|
FETCH_OP_FIX_PC: begin
|
| 723 |
|
|
if (page_crossed) begin
|
| 724 |
|
|
next_state = FETCH_OP;
|
| 725 |
|
|
end
|
| 726 |
|
|
else begin
|
| 727 |
|
|
next_state = FETCH_LOW;
|
| 728 |
|
|
end
|
| 729 |
|
|
end
|
| 730 |
|
|
FETCH_HIGH_CALC_INDEX: begin
|
| 731 |
|
|
next_state = READ_MEM_FIX_ADDR;
|
| 732 |
|
|
end
|
| 733 |
|
|
READ_MEM_FIX_ADDR: begin
|
| 734 |
|
|
if (read) begin
|
| 735 |
|
|
if (page_crossed) begin
|
| 736 |
|
|
next_state = READ_MEM;
|
| 737 |
|
|
end
|
| 738 |
|
|
else begin
|
| 739 |
|
|
next_state = FETCH_OP_CALC_PARAM;
|
| 740 |
|
|
end
|
| 741 |
|
|
end
|
| 742 |
|
|
else if (read_modify_write) begin
|
| 743 |
|
|
next_state = READ_MEM;
|
| 744 |
|
|
end
|
| 745 |
|
|
else if (write) begin
|
| 746 |
|
|
next_state = WRITE_MEM;
|
| 747 |
|
|
alu_enable = 1'b1;
|
| 748 |
|
|
alu_opcode = ir;
|
| 749 |
|
|
end
|
| 750 |
|
|
else begin
|
| 751 |
|
|
//$write("unknown behavior");
|
| 752 |
|
|
//$finish(0);
|
| 753 |
|
|
end
|
| 754 |
|
|
end
|
| 755 |
|
|
FETCH_HIGH: begin
|
| 756 |
|
|
if (jump_indirect) begin
|
| 757 |
|
|
next_state = READ_FROM_POINTER;
|
| 758 |
|
|
end
|
| 759 |
|
|
else if (jump) begin
|
| 760 |
|
|
next_state = FETCH_OP;
|
| 761 |
|
|
end
|
| 762 |
|
|
else if (read || read_modify_write) begin
|
| 763 |
|
|
next_state = READ_MEM;
|
| 764 |
|
|
end
|
| 765 |
|
|
else if (write) begin
|
| 766 |
|
|
next_state = WRITE_MEM;
|
| 767 |
|
|
end
|
| 768 |
|
|
else begin
|
| 769 |
|
|
//$write("unknown behavior");
|
| 770 |
|
|
//$finish(0);
|
| 771 |
|
|
end
|
| 772 |
|
|
end
|
| 773 |
|
|
READ_MEM_CALC_INDEX: begin
|
| 774 |
|
|
if (read || read_modify_write) begin
|
| 775 |
|
|
next_state = READ_MEM;
|
| 776 |
|
|
end
|
| 777 |
|
|
else if (write) begin
|
| 778 |
|
|
alu_opcode = ir;
|
| 779 |
|
|
alu_enable = 1'b1;
|
| 780 |
|
|
next_state = WRITE_MEM;
|
| 781 |
|
|
end
|
| 782 |
|
|
else begin
|
| 783 |
|
|
//$write("unknown behavior");
|
| 784 |
|
|
//$finish(0);
|
| 785 |
|
|
end
|
| 786 |
|
|
end
|
| 787 |
|
|
READ_MEM: begin
|
| 788 |
|
|
if (read) begin
|
| 789 |
|
|
next_state = FETCH_OP_CALC_PARAM;
|
| 790 |
|
|
end
|
| 791 |
|
|
else if (read_modify_write) begin
|
| 792 |
|
|
next_state = DUMMY_WRT_CALC;
|
| 793 |
|
|
end
|
| 794 |
|
|
end
|
| 795 |
|
|
DUMMY_WRT_CALC: begin
|
| 796 |
|
|
alu_opcode = ir;
|
| 797 |
|
|
alu_enable = 1'b1;
|
| 798 |
|
|
alu_a = data_in;
|
| 799 |
|
|
next_state = WRITE_MEM;
|
| 800 |
|
|
end
|
| 801 |
|
|
WRITE_MEM: begin
|
| 802 |
|
|
next_state = FETCH_OP;
|
| 803 |
|
|
end
|
| 804 |
|
|
PUSH_PCH: begin
|
| 805 |
|
|
next_state = PUSH_PCL;
|
| 806 |
|
|
end
|
| 807 |
|
|
PUSH_PCL: begin
|
| 808 |
|
|
if (jsr) begin
|
| 809 |
|
|
next_state = FETCH_HIGH;
|
| 810 |
|
|
end
|
| 811 |
|
|
else begin
|
| 812 |
|
|
next_state = PUSH_STATUS;
|
| 813 |
|
|
end
|
| 814 |
|
|
end
|
| 815 |
|
|
PUSH_STATUS: begin
|
| 816 |
|
|
next_state = FETCH_PCL;
|
| 817 |
|
|
end
|
| 818 |
|
|
FETCH_PCL: begin
|
| 819 |
|
|
next_state = FETCH_PCH;
|
| 820 |
|
|
end
|
| 821 |
|
|
FETCH_PCH: begin
|
| 822 |
|
|
next_state = FETCH_OP;
|
| 823 |
|
|
end
|
| 824 |
|
|
INCREMENT_SP: begin
|
| 825 |
|
|
if (rti) begin
|
| 826 |
|
|
next_state = PULL_STATUS;
|
| 827 |
|
|
end
|
| 828 |
|
|
else if (pla || plp) begin
|
| 829 |
|
|
next_state = PULL_REGISTER;
|
| 830 |
|
|
end
|
| 831 |
|
|
else begin // rts
|
| 832 |
|
|
next_state = PULL_PCL;
|
| 833 |
|
|
end
|
| 834 |
|
|
end
|
| 835 |
|
|
PULL_STATUS: begin
|
| 836 |
|
|
next_state = PULL_PCL;
|
| 837 |
|
|
end
|
| 838 |
|
|
PULL_PCL: begin
|
| 839 |
|
|
next_state = PULL_PCH;
|
| 840 |
202 |
creep |
|
| 841 |
|
|
if (rti) begin
|
| 842 |
|
|
alu_opcode = ir;
|
| 843 |
|
|
alu_enable = 1'b1;
|
| 844 |
|
|
alu_a = temp_data;
|
| 845 |
|
|
end
|
| 846 |
128 |
gabrielosh |
end
|
| 847 |
|
|
PULL_PCH: begin
|
| 848 |
|
|
if (rti) begin
|
| 849 |
|
|
next_state = FETCH_OP;
|
| 850 |
|
|
end
|
| 851 |
|
|
else begin // rts
|
| 852 |
|
|
next_state = INCREMENT_PC;
|
| 853 |
|
|
end
|
| 854 |
|
|
end
|
| 855 |
|
|
INCREMENT_PC: begin
|
| 856 |
|
|
next_state = FETCH_OP;
|
| 857 |
|
|
end
|
| 858 |
|
|
PUSH_REGISTER: begin
|
| 859 |
|
|
next_state = FETCH_OP;
|
| 860 |
|
|
end
|
| 861 |
|
|
PULL_REGISTER: begin
|
| 862 |
|
|
next_state = FETCH_OP_CALC_PARAM;
|
| 863 |
|
|
end
|
| 864 |
|
|
DUMMY: begin
|
| 865 |
|
|
next_state = PUSH_PCH;
|
| 866 |
|
|
end
|
| 867 |
|
|
default: begin
|
| 868 |
|
|
next_state = RESET;
|
| 869 |
|
|
end
|
| 870 |
|
|
endcase
|
| 871 |
|
|
end
|
| 872 |
|
|
|
| 873 |
|
|
// this always block is responsible for updating the address mode and the type of operation being done
|
| 874 |
|
|
always @ (*) begin //
|
| 875 |
|
|
absolute = 1'b0;
|
| 876 |
|
|
absolute_indexed = 1'b0;
|
| 877 |
|
|
accumulator = 1'b0;
|
| 878 |
|
|
immediate = 1'b0;
|
| 879 |
|
|
implied = 1'b0;
|
| 880 |
|
|
indirectx = 1'b0;
|
| 881 |
|
|
indirecty = 1'b0;
|
| 882 |
|
|
relative = 1'b0;
|
| 883 |
|
|
zero_page = 1'b0;
|
| 884 |
|
|
zero_page_indexed = 1'b0;
|
| 885 |
|
|
|
| 886 |
|
|
index = 8'h00;
|
| 887 |
|
|
|
| 888 |
|
|
read = 1'b0;
|
| 889 |
|
|
read_modify_write = 1'b0;
|
| 890 |
|
|
write = 1'b0;
|
| 891 |
|
|
jump = 1'b0;
|
| 892 |
|
|
jump_indirect = 1'b0;
|
| 893 |
|
|
branch = 1'b0;
|
| 894 |
|
|
|
| 895 |
|
|
brk = 1'b0;
|
| 896 |
|
|
rti = 1'b0;
|
| 897 |
|
|
rts = 1'b0;
|
| 898 |
|
|
pha = 1'b0;
|
| 899 |
|
|
php = 1'b0;
|
| 900 |
|
|
pla = 1'b0;
|
| 901 |
|
|
plp = 1'b0;
|
| 902 |
|
|
jsr = 1'b0;
|
| 903 |
194 |
creep |
tsx = 1'b0;
|
| 904 |
|
|
txs = 1'b0;
|
| 905 |
205 |
creep |
nop = 1'b0;
|
| 906 |
128 |
gabrielosh |
|
| 907 |
|
|
case (ir)
|
| 908 |
205 |
creep |
CLC_IMP, CLD_IMP, CLI_IMP, CLV_IMP, DEX_IMP, DEY_IMP, INX_IMP, INY_IMP, SEC_IMP, SED_IMP, SEI_IMP, TAX_IMP,
|
| 909 |
|
|
TAY_IMP, TXA_IMP, TYA_IMP: begin
|
| 910 |
128 |
gabrielosh |
implied = 1'b1;
|
| 911 |
|
|
end
|
| 912 |
205 |
creep |
NOP_IMP: begin
|
| 913 |
|
|
implied = 1'b1;
|
| 914 |
|
|
nop = 1'b1;
|
| 915 |
|
|
end
|
| 916 |
128 |
gabrielosh |
ASL_ACC, LSR_ACC, ROL_ACC, ROR_ACC: begin
|
| 917 |
|
|
accumulator = 1'b1;
|
| 918 |
|
|
end
|
| 919 |
|
|
ADC_IMM, AND_IMM, CMP_IMM, CPX_IMM, CPY_IMM, EOR_IMM, LDA_IMM, LDX_IMM, LDY_IMM, ORA_IMM, SBC_IMM: begin
|
| 920 |
|
|
immediate = 1'b1;
|
| 921 |
|
|
end
|
| 922 |
|
|
ADC_ZPG, AND_ZPG, ASL_ZPG, BIT_ZPG, CMP_ZPG, CPX_ZPG, CPY_ZPG, DEC_ZPG, EOR_ZPG, INC_ZPG, LDA_ZPG, LDX_ZPG, LDY_ZPG,
|
| 923 |
|
|
LSR_ZPG, ORA_ZPG, ROL_ZPG, ROR_ZPG, SBC_ZPG, STA_ZPG, STX_ZPG, STY_ZPG: begin
|
| 924 |
|
|
zero_page = 1'b1;
|
| 925 |
|
|
end
|
| 926 |
|
|
ADC_ZPX, AND_ZPX, ASL_ZPX, CMP_ZPX, DEC_ZPX, EOR_ZPX, INC_ZPX, LDA_ZPX, LDY_ZPX, LSR_ZPX, ORA_ZPX, ROL_ZPX, ROR_ZPX,
|
| 927 |
|
|
SBC_ZPX, STA_ZPX, STY_ZPX: begin
|
| 928 |
|
|
zero_page_indexed = 1'b1;
|
| 929 |
|
|
index = alu_x;
|
| 930 |
|
|
end
|
| 931 |
|
|
LDX_ZPY, STX_ZPY: begin
|
| 932 |
|
|
zero_page_indexed = 1'b1;
|
| 933 |
|
|
index = alu_y;
|
| 934 |
|
|
end
|
| 935 |
|
|
BCC_REL: begin
|
| 936 |
|
|
relative = 1'b1;
|
| 937 |
|
|
index = temp_data;
|
| 938 |
|
|
|
| 939 |
|
|
if (!alu_status[C]) begin
|
| 940 |
|
|
branch = 1'b1;
|
| 941 |
|
|
end
|
| 942 |
|
|
else begin
|
| 943 |
|
|
branch = 1'b0;
|
| 944 |
|
|
end
|
| 945 |
|
|
end
|
| 946 |
|
|
BCS_REL: begin
|
| 947 |
|
|
relative = 1'b1;
|
| 948 |
|
|
index = temp_data;
|
| 949 |
|
|
|
| 950 |
|
|
if (alu_status[C]) begin
|
| 951 |
|
|
branch = 1'b1;
|
| 952 |
|
|
end
|
| 953 |
|
|
else begin
|
| 954 |
|
|
branch = 1'b0;
|
| 955 |
|
|
end
|
| 956 |
|
|
end
|
| 957 |
|
|
BEQ_REL: begin
|
| 958 |
|
|
relative = 1'b1;
|
| 959 |
|
|
index = temp_data;
|
| 960 |
|
|
|
| 961 |
|
|
if (alu_status[Z]) begin
|
| 962 |
|
|
branch = 1'b1;
|
| 963 |
|
|
end
|
| 964 |
|
|
else begin
|
| 965 |
|
|
branch = 1'b0;
|
| 966 |
|
|
end
|
| 967 |
|
|
end
|
| 968 |
|
|
BNE_REL: begin
|
| 969 |
|
|
relative = 1'b1;
|
| 970 |
|
|
index = temp_data;
|
| 971 |
|
|
|
| 972 |
|
|
if (alu_status[Z] == 1'b0) begin
|
| 973 |
|
|
branch = 1'b1;
|
| 974 |
|
|
end
|
| 975 |
|
|
else begin
|
| 976 |
|
|
branch = 1'b0;
|
| 977 |
|
|
end
|
| 978 |
|
|
end
|
| 979 |
|
|
BPL_REL: begin
|
| 980 |
|
|
relative = 1'b1;
|
| 981 |
|
|
index = temp_data;
|
| 982 |
|
|
|
| 983 |
|
|
if (!alu_status[N]) begin
|
| 984 |
|
|
branch = 1'b1;
|
| 985 |
|
|
end
|
| 986 |
|
|
else begin
|
| 987 |
|
|
branch = 1'b0;
|
| 988 |
|
|
end
|
| 989 |
|
|
end
|
| 990 |
|
|
BMI_REL: begin
|
| 991 |
|
|
relative = 1'b1;
|
| 992 |
|
|
index = temp_data;
|
| 993 |
|
|
|
| 994 |
|
|
if (alu_status[N]) begin
|
| 995 |
|
|
branch = 1'b1;
|
| 996 |
|
|
end
|
| 997 |
|
|
else begin
|
| 998 |
|
|
branch = 1'b0;
|
| 999 |
|
|
end
|
| 1000 |
|
|
end
|
| 1001 |
|
|
BVC_REL: begin
|
| 1002 |
|
|
relative = 1'b1;
|
| 1003 |
|
|
index = temp_data;
|
| 1004 |
|
|
|
| 1005 |
|
|
if (!alu_status[V]) begin
|
| 1006 |
|
|
branch = 1'b1;
|
| 1007 |
|
|
end
|
| 1008 |
|
|
else begin
|
| 1009 |
|
|
branch = 1'b0;
|
| 1010 |
|
|
end
|
| 1011 |
|
|
end
|
| 1012 |
|
|
BVS_REL: begin
|
| 1013 |
|
|
relative = 1'b1;
|
| 1014 |
|
|
index = temp_data;
|
| 1015 |
|
|
|
| 1016 |
|
|
if (alu_status[V]) begin
|
| 1017 |
|
|
branch = 1'b1;
|
| 1018 |
|
|
end
|
| 1019 |
|
|
else begin
|
| 1020 |
|
|
branch = 1'b0;
|
| 1021 |
|
|
end
|
| 1022 |
|
|
end
|
| 1023 |
|
|
ADC_ABS, AND_ABS, ASL_ABS, BIT_ABS, CMP_ABS, CPX_ABS, CPY_ABS, DEC_ABS, EOR_ABS, INC_ABS, LDA_ABS,
|
| 1024 |
|
|
LDX_ABS, LDY_ABS, LSR_ABS, ORA_ABS, ROL_ABS, ROR_ABS, SBC_ABS, STA_ABS, STX_ABS, STY_ABS: begin
|
| 1025 |
|
|
absolute = 1'b1;
|
| 1026 |
|
|
end
|
| 1027 |
|
|
ADC_ABX, AND_ABX, ASL_ABX, CMP_ABX, DEC_ABX, EOR_ABX, INC_ABX, LDA_ABX, LDY_ABX, LSR_ABX, ORA_ABX, ROL_ABX, ROR_ABX,
|
| 1028 |
|
|
SBC_ABX, STA_ABX: begin
|
| 1029 |
|
|
absolute_indexed = 1'b1;
|
| 1030 |
|
|
index = alu_x;
|
| 1031 |
|
|
end
|
| 1032 |
|
|
ADC_ABY, AND_ABY, CMP_ABY, EOR_ABY, LDA_ABY, LDX_ABY, ORA_ABY, SBC_ABY, STA_ABY: begin
|
| 1033 |
|
|
absolute_indexed = 1'b1;
|
| 1034 |
|
|
index = alu_y;
|
| 1035 |
|
|
end
|
| 1036 |
|
|
ADC_IDX, AND_IDX, CMP_IDX, EOR_IDX, LDA_IDX, ORA_IDX, SBC_IDX, STA_IDX: begin
|
| 1037 |
|
|
indirectx = 1'b1;
|
| 1038 |
|
|
index = alu_x;
|
| 1039 |
|
|
end
|
| 1040 |
|
|
ADC_IDY, AND_IDY, CMP_IDY, EOR_IDY, LDA_IDY, ORA_IDY, SBC_IDY, STA_IDY: begin
|
| 1041 |
|
|
indirecty = 1'b1;
|
| 1042 |
|
|
index = alu_y;
|
| 1043 |
|
|
end
|
| 1044 |
|
|
JMP_ABS: begin
|
| 1045 |
|
|
absolute = 1'b1;
|
| 1046 |
|
|
jump = 1'b1;
|
| 1047 |
|
|
end
|
| 1048 |
|
|
JMP_IND: begin
|
| 1049 |
|
|
jump_indirect = 1'b1;
|
| 1050 |
|
|
end
|
| 1051 |
|
|
BRK_IMP: begin
|
| 1052 |
|
|
brk = 1'b1;
|
| 1053 |
|
|
end
|
| 1054 |
|
|
RTI_IMP: begin
|
| 1055 |
|
|
rti = 1'b1;
|
| 1056 |
|
|
end
|
| 1057 |
|
|
RTS_IMP: begin
|
| 1058 |
|
|
rts = 1'b1;
|
| 1059 |
|
|
end
|
| 1060 |
|
|
PHA_IMP: begin
|
| 1061 |
|
|
pha = 1'b1;
|
| 1062 |
|
|
end
|
| 1063 |
|
|
PHP_IMP: begin
|
| 1064 |
|
|
php = 1'b1;
|
| 1065 |
|
|
end
|
| 1066 |
|
|
PLA_IMP: begin
|
| 1067 |
|
|
pla = 1'b1;
|
| 1068 |
|
|
end
|
| 1069 |
|
|
PLP_IMP: begin
|
| 1070 |
|
|
plp = 1'b1;
|
| 1071 |
|
|
end
|
| 1072 |
|
|
JSR_ABS: begin
|
| 1073 |
|
|
jsr = 1'b1;
|
| 1074 |
|
|
end
|
| 1075 |
194 |
creep |
TSX_IMP: begin
|
| 1076 |
|
|
tsx = 1'b1;
|
| 1077 |
|
|
end
|
| 1078 |
|
|
TXS_IMP: begin
|
| 1079 |
|
|
txs = 1'b1;
|
| 1080 |
|
|
end
|
| 1081 |
128 |
gabrielosh |
default: begin
|
| 1082 |
|
|
//$write("state : %b", state);
|
| 1083 |
|
|
if (reset_n == 1'b1 && state != FETCH_OP_FIX_PC) begin // the processor is NOT being reset neither it is fixing the pc
|
| 1084 |
|
|
//$write("\nunknown OPCODE!!!!! 0x%h\n", ir);
|
| 1085 |
|
|
//$finish();
|
| 1086 |
|
|
end
|
| 1087 |
|
|
end
|
| 1088 |
|
|
endcase
|
| 1089 |
|
|
|
| 1090 |
|
|
case (ir)
|
| 1091 |
|
|
ASL_ACC, ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX, LSR_ACC, LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX, ROL_ACC, ROL_ZPG, ROL_ZPX, ROL_ABS,
|
| 1092 |
|
|
ROL_ABX, ROR_ACC, ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX, INC_ZPG, INC_ZPX, INC_ABS, INC_ABX, DEC_ZPG, DEC_ZPX, DEC_ABS,
|
| 1093 |
|
|
DEC_ABX: begin
|
| 1094 |
|
|
read_modify_write = 1'b1;
|
| 1095 |
|
|
end
|
| 1096 |
|
|
STA_ZPG, STA_ZPX, STA_ABS, STA_ABX, STA_ABY, STA_IDX, STA_IDY, STX_ZPG, STX_ZPY, STX_ABS, STY_ZPG, STY_ZPX, STY_ABS: begin
|
| 1097 |
|
|
write = 1'b1;
|
| 1098 |
|
|
end
|
| 1099 |
|
|
default: begin // this should work fine since the previous case statement will detect the unknown/undocumented/unsupported opcodes
|
| 1100 |
|
|
read = 1'b1;
|
| 1101 |
|
|
end
|
| 1102 |
|
|
endcase
|
| 1103 |
|
|
end
|
| 1104 |
|
|
endmodule
|
| 1105 |
|
|
|
| 1106 |
|
|
|
| 1107 |
|
|
|
