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Add decoder

master
Denis Tereshkin 2 years ago
parent
8ccea9566e
commit
064b1c0727
3 changed files with 278 additions and 22 deletions
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  1. 17
      src/alu.verilog
  2. 171
      src/decoder.verilog
  3. 90
      src/parameters.vh

17
src/alu.verilog
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@ -13,17 +13,6 @@ module alu @@ -13,17 +13,6 @@ module alu
output reg r_c
);
localparam OP_OR = 0;
localparam OP_AND = 1;
localparam OP_EOR = 2;
localparam OP_ADC = 3;
localparam OP_SUB = 4;
localparam OP_ROT = 5;
localparam OP_SHF = 6;
localparam SHIFT_LEFT = 0;
localparam SHIFT_RIGHT = 1;
wire rst = !nrst;
reg [8:0] buffer;
wire [8:0] sum;
@ -35,6 +24,12 @@ module alu @@ -35,6 +24,12 @@ module alu
assign sum = A + B + C;
assign diff = A - B - (1 - C);
initial begin
buffer <= 0;
r_v <= 0;
r_c <= 0;
end
always @(posedge clk)
begin
case (sel)

171
src/decoder.verilog
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@ -0,0 +1,171 @@ @@ -0,0 +1,171 @@
module decoder
(
input clk,
input rst,
input [7:0] instr,
output reg [3:0] address_code,
output reg [7:0] decoded
);
`include "parameters.vh"
wire [2:0] row = instr[7:5];
wire [2:0] column = instr[4:2];
wire [1:0] sector = instr[1:0];
wire sec_2_stp = (sector == 2) && ((column == 0 && row <= 3) || (column == 4));
wire sec_2_nop = (sector == 2) && ((column == 0 && (row == 4 || row == 6 || row == 7))
|| (column == 6 && (row != 4 && row != 5)));
always @* begin
if (rst) begin
address_code <= 0;
end
else begin
if (sector == 1) begin
case (row)
0: decoded <= I_ORA;
1: decoded <= I_AND;
2: decoded <= I_EOR;
3: decoded <= I_ADC;
4: decoded <= (column == 2 ? I_STA : I_NOP);
5: decoded <= I_LDA;
6: decoded <= I_CMP;
7: decoded <= I_SBC;
endcase
address_code <= column;
end
else if (sector == 2) begin
case (row)
0: decoded <= (sec_2_stp ? I_STP : (sec_2_nop ? I_NOP : I_ASL));
1: decoded <= (sec_2_stp ? I_STP : (sec_2_nop ? I_NOP : I_ROL));
2: decoded <= (sec_2_stp ? I_STP : (sec_2_nop ? I_NOP : I_LSR));
3: decoded <= (sec_2_stp ? I_STP : (sec_2_nop ? I_NOP : I_ROR));
4: decoded <= (sec_2_stp ? I_STP : (sec_2_nop ? I_NOP : (column[0] ? I_STX : I_TXA)));
5: decoded <= (sec_2_stp ? I_STP : (column == 2 ? I_TAX : (column == 6 ? I_TSX : I_LDX)));
6: decoded <= (sec_2_stp ? I_STP : (sec_2_nop ? I_NOP : (column == 2 ? I_DEX : I_DEC)));
7: decoded <= (sec_2_stp ? I_STP : ((sec_2_nop || column == 2) ? I_NOP : I_INC));
endcase
if (column > 0) begin
address_code <= column
end
else begin
address_code <= ADDR_MODE_IMMEDIATE;
end
end
else if (sector == 0) begin
if (column == 0) begin
case (row)
0: decoded <= I_BRK;
1: decoded <= I_JSR;
2: decoded <= I_RTI;
3: decoded <= I_RTS;
4: decoded <= I_NOP;
5: decoded <= I_LDY;
6: decoded <= I_CPY;
7: decoded <= I_CPX;
endcase
end
else if (column == 1) begin
case (row)
0: decoded <= I_NOP;
1: decoded <= I_BIT;
2: decoded <= I_NOP;
3: decoded <= I_NOP;
4: decoded <= I_STY;
5: decoded <= I_LDY;
6: decoded <= I_CPY;
7: decoded <= I_CPX;
endcase
end
else if (column == 2) begin
case (row)
0: decoded <= I_PHP;
1: decoded <= I_PLP;
2: decoded <= I_PHA;
3: decoded <= I_PLA;
4: decoded <= I_DEY;
5: decoded <= I_TAY;
6: decoded <= I_INY;
7: decoded <= I_INX;
endcase
end
else if (column == 3) begin
case (row)
0: decoded <= I_NOP;
1: decoded <= I_BIT;
2: decoded <= I_JMP;
3: decoded <= I_JMP;
4: decoded <= I_STY;
5: decoded <= I_LDY;
6: decoded <= I_CPY;
7: decoded <= I_CPX;
endcase
end
else if (column == 4) begin
case (row)
0: decoded <= I_BPL;
1: decoded <= I_BMI;
2: decoded <= I_BVC;
3: decoded <= I_BVS;
4: decoded <= I_BCC;
5: decoded <= I_BCS;
6: decoded <= I_BNE;
7: decoded <= I_BEQ;
endcase
end
else if (column == 5) begin
case (row)
0: decoded <= I_NOP;
1: decoded <= I_NOP;
2: decoded <= I_NOP;
3: decoded <= I_NOP;
4: decoded <= I_STY;
5: decoded <= I_LDY;
6: decoded <= I_NOP;
7: decoded <= I_NOP;
endcase
end
else if (column == 6) begin
case (row)
0: decoded <= I_CLC;
1: decoded <= I_SEC;
2: decoded <= I_CLI;
3: decoded <= I_SEI;
4: decoded <= I_TYA;
5: decoded <= I_CLV;
6: decoded <= I_CLD;
7: decoded <= I_SED;
endcase
end
else if (column == 7) begin
case (row)
0: decoded <= I_NOP;
1: decoded <= I_NOP;
2: decoded <= I_NOP;
3: decoded <= I_NOP;
4: decoded <= I_SHY;
5: decoded <= I_LDY;
6: decoded <= I_NOP;
7: decoded <= I_NOP;
endcase
end
if (column > 0) begin
address_code <= column;
end
else begin
if (row >= 4) begin
address_code <= ADDR_MODE_IMMEDIATE;
end
else begin
address_code <= ADDR_MODE_ABSOLUTE;
end
end
end
end
end
endmodule

90
src/parameters.vh
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@ -0,0 +1,90 @@ @@ -0,0 +1,90 @@
parameter ADDR_MODE_INDEXED_INDIRECT = 0;
parameter ADDR_MODE_ZP = 1;
parameter ADDR_MODE_IMMEDIATE = 2;
parameter ADDR_MODE_ABSOLUTE = 3;
parameter ADDR_MODE_INDIRECT_INDEXED = 4;
parameter ADDR_MODE_ZP_X = 5;
parameter ADDR_MODE_ABS_Y = 6;
parameter ADDR_MODE_ABS_X = 7;
parameter OP_OR = 0;
parameter OP_AND = 1;
parameter OP_EOR = 2;
parameter OP_ADC = 3;
parameter OP_SUB = 4;
parameter OP_ROT = 5;
parameter OP_SHF = 6;
parameter SHIFT_LEFT = 0;
parameter SHIFT_RIGHT = 1;
parameter I_LDA = 0;
parameter I_LDX = 1;
parameter I_LDY = 2;
parameter I_STA = 3;
parameter I_STX = 4;
parameter I_STY = 5;
parameter I_TAX = 6;
parameter I_TAY = 7;
parameter I_TXA = 8;
parameter I_TYA = 9;
parameter I_TSX = 10;
parameter I_TXS = 11;
parameter I_PHA = 12;
parameter I_PHP = 13;
parameter I_PLA = 14;
parameter I_PLP = 15;
parameter I_AND = 16;
parameter I_EOR = 17;
parameter I_ORA = 18;
parameter I_BIT = 19;
parameter I_ADC = 20;
parameter I_SBC = 21;
parameter I_CMP = 22;
parameter I_CPX = 23;
parameter I_CPY = 24;
parameter I_INC = 25;
parameter I_INX = 26;
parameter I_INY = 27;
parameter I_DEC = 28;
parameter I_DEX = 29;
parameter I_DEY = 30;
parameter I_ASL = 31;
parameter I_LSR = 32;
parameter I_ROL = 33;
parameter I_ROR = 34;
parameter I_JMP = 35;
parameter I_JSR = 36;
parameter I_RTS = 37;
parameter I_BCC = 38;
parameter I_BCS = 39;
parameter I_BEQ = 40;
parameter I_BMI = 41;
parameter I_BNE = 42;
parameter I_BPL = 43;
parameter I_BVC = 44;
parameter I_BVS = 45;
parameter I_CLC = 46;
parameter I_CLD = 47;
parameter I_CLI = 48;
parameter I_CLV = 49;
parameter I_SEC = 50;
parameter I_SED = 51;
parameter I_SEI = 52;
parameter I_BRK = 53;
parameter I_NOP = 54;
parameter I_RTI = 55;
// Unofficial opcodes
parameter I_STP = 56;
parameter I_SHY = 57;
parameter P_N = 8'h80;
parameter P_V = 8'h40;
parameter P_B = 8'h10;
parameter P_D = 8'h08;
parameter P_I = 8'h04;
parameter P_Z = 8'h02;
parameter P_C = 8'h01;
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