383 lines
14 KiB
Systemverilog
383 lines
14 KiB
Systemverilog
module yayacemu (
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input wire clk_in
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);
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import "DPI-C" function void init_screen();
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wire [31:0] vram [0:2047];
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bit [7:0] memory [0:4095];
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wire [7:0] registers [0:15];
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logic [3:0] stack_pointer;
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wire [15:0] stack [0:15];
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logic [7:0] delay_timer;
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logic [7:0] sound_timer;
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bit keyboard [15:0];
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int cycle_counter;
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bit halt;
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int watch_key;
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logic [15:0] index_reg;
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bit [7:0] rand_num;
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logic rom_ready;
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logic [15:0] program_counter;
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randomizer randy(clk_in, program_counter, keyboard, cycle_counter, rand_num);
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keyboard kb(clk_in, keyboard);
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rom_loader rl (memory, rom_ready);
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chip8_cpu cpu (memory, clk_in, keyboard, rand_num, vram, stack, index_reg, stack_pointer, registers, delay_timer, sound_timer, cycle_counter, program_counter, halt, watch_key);
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chip8_gpu gpu (vram, sound_timer);
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int i;
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initial begin
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watch_key = 255;
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halt = 0;
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for(i = 0; i < 15; i++) begin
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keyboard[i] = 0;
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end
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sound_timer = 0;
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delay_timer = 0;
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cycle_counter = 0;
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program_counter = 'h200;
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stack_pointer = 4'b0000;
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init_screen();
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end
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endmodule
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module keyboard (
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input wire clk_in,
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output bit keyboard [15:0]
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);
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int i;
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import "DPI-C" function bit [7:0] get_key();
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bit[7:0] keyval;
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always_ff @(posedge clk_in) begin
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keyval = get_key();
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if (keyval != 8'b11111111) begin
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keyboard[keyval[3:0]] = keyval[7];
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end
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end
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endmodule
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module chip8_cpu(
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output bit [7:0] memory [0:4095],
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input wire clk_in,
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input wire keyboard [15:0],
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input wire [7:0] random_number,
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output wire [31:0] vram [0:2047],
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output wire [15:0] stack [0:15],
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output wire [15:0] index_reg,
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output wire [3:0] stack_pointer,
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output wire [7:0] registers [0:15],
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output logic [7:0] delay_timer,
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output logic [7:0] sound_timer,
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output int cycle_counter,
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output wire [15:0] program_counter,
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output bit halt,
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output int watch_key
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);
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logic [15:0] opcode;
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logic [15:0] scratch;
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logic [15:0] scratch2;
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logic [7:0] scratch_8;
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logic [7:0] scratch_82;
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logic [31:0] x_cord;
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logic [31:0] y_cord;
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logic [7:0] size;
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logic [31:0] screen_pixel;
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logic [7:0] sprite_pixel;
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int i;
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logic [7:0] i8;
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int r;
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int c;
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always_ff @(posedge clk_in) begin
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opcode = {memory[program_counter+0], memory[program_counter+1]};
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$display("HW : opcode is 0x%h (%b)", opcode, opcode);
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$display("HW : PC %0d 0x%h", program_counter, program_counter);
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// 480Hz / 8 = 60 Hz
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if (cycle_counter % 20 == 0) begin
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if (delay_timer > 0)
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delay_timer--;
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if (sound_timer > 0)
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sound_timer--;
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end
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casez(opcode)
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'h00E0: begin
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$display("HW : INSTR CLS");
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for(i = 0; i < 2048; i++) begin
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vram[i] = 0;
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end
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end
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'h00EE: begin
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$display("HW : INSTR RET");
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stack_pointer--;
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program_counter = stack[stack_pointer];
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end
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'h0???: $display("HW : INSTR SYS addr (Treating as NOP)");
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'h1???: begin
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$display("HW : INSTR JP addr");
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program_counter = (opcode & 'h0FFF) - 2;
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end
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'h2???: begin
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$display("HW : INSTR CALL addr");
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stack[stack_pointer] = program_counter;
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stack_pointer++;
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program_counter = (opcode & 'h0FFF) - 2;
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end
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'h3???: begin
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$display("HW : INSTR SE Vx, byte");
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scratch = (opcode & 'h00FF);
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if (scratch[7:0] == registers[(opcode & 'h0F00) >> 8]) begin
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program_counter += 2;
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end
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end
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'h4???: begin
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$display("HW : INSTR SNE Vx, byte");
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scratch = (opcode & 'h00FF);
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if (scratch[7:0] != registers[(opcode & 'h0F00) >> 8]) begin
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program_counter += 2;
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end
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end
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'h5??0: begin
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$display("HW : INSTR SE Vx, Vy");
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if (registers[(opcode & 'h00F0) >> 4] == registers[(opcode & 'h0F00) >> 8]) begin
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program_counter += 2;
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end
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end
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'h6???: begin
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$display("HW : INSTR LD Vx, byte");
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scratch = (opcode & 'h00FF);
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registers[(opcode & 'h0F00) >> 8] = scratch[7:0];
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end
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'h7???: begin
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$display("HW : INSTR ADD Vx, byte");
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scratch = (opcode & 'h00FF);
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registers[(opcode & 'h0F00) >> 8] += scratch[7:0];
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end
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'h8??0: begin
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$display("HW : INSTR LD Vx, Vy");
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registers[(opcode & 'h0F00) >> 8] = registers[(opcode & 'h00F0) >> 4];
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end
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'h8??1: begin
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$display("HW : INSTR OR Vx, Vy");
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registers[(opcode & 'h0F00) >> 8] |= registers[(opcode & 'h00F0) >> 4];
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registers[15] = 0;
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end
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'h8??2: begin
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$display("HW : INSTR AND Vx, Vy");
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registers[(opcode & 'h0F00) >> 8] &= registers[(opcode & 'h00F0) >> 4];
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registers[15] = 0;
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end
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'h8??3: begin
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$display("HW : INSTR XOR Vx, Vy");
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registers[(opcode & 'h0F00) >> 8] ^= registers[(opcode & 'h00F0) >> 4];
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registers[15] = 0;
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end
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'h8??4: begin
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$display("HW : INSTR ADD Vx, Vy");
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scratch_8 = registers[(opcode & 'h0F00) >> 8];
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registers[(opcode & 'h0F00) >> 8] += registers[(opcode & 'h00F0) >> 4];
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registers[15] = {7'b0000000, scratch_8 > registers[(opcode & 'h0F00) >> 8]};
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end
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'h8??5: begin
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$display("HW : INSTR SUB Vx, Vy");
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scratch_8 = registers[(opcode & 'h0F00) >> 8];
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registers[(opcode & 'h0F00) >> 8] -= registers[(opcode & 'h00F0) >> 4];
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registers[15] = {7'b0000000, scratch_8 >= registers[(opcode & 'h0F00) >> 8]};
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end
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'h8??6: begin
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$display("HW : INSTR SHR Vx {, Vy}");
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scratch_8 = registers[(opcode & 'h0F00) >> 8];
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registers[(opcode & 'h0F00) >> 8] = registers[(opcode & 'h00F0) >> 4]>> 1;
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registers[15] = {7'b0000000, ((scratch_8 & 8'h01) == 8'h01)};
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end
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'h8??7: begin
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$display("HW : INSTR SUBN Vx, Vy");
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scratch_8 = registers[(opcode & 'h00F0) >> 4];
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scratch_82 = registers[(opcode & 'h0F00) >> 8];
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registers[(opcode & 'h0F00) >> 8] = registers[(opcode & 'h00F0) >> 4] - registers[(opcode & 'h0F00) >> 8];
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registers[15] = {7'b0000000, (scratch_8 >= scratch_82)};
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end
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'h8??E: begin
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$display("HW : INSTR SHL Vx {, Vy}");
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scratch_8 = registers[(opcode & 'h0F00) >> 8];
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registers[(opcode & 'h0F00) >> 8] = registers[(opcode & 'h00F0) >> 4]<< 1;
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registers[15] = {7'b0000000, (scratch_8[7]) };
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end
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'h9??0: begin
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$display("HW : INSTR SNE Vx, Vy");
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if (registers[(opcode & 'h00F0) >> 4] != registers[(opcode & 'h0F00) >> 8]) begin
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program_counter += 2;
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end
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end
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'hA???: begin
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$display("HW : INSTR LD I, addr");
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index_reg = (opcode & 'h0FFF);
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end
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'hb???: begin
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$display("HW : INSTR JP V0, addr");
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program_counter = {8'h00, registers[0]} + (opcode & 'h0FFF) - 2;
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end
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'hc???: begin
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$display("HW : RND Vx, addr");
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// TODO: use a real RNG module, this is not synthesizeable
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scratch = {8'h00, random_number} % 16'h0100;
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scratch2 = (opcode & 'h00FF);
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registers[(opcode & 'h0F00) >> 8] = scratch[7:0] & scratch2[7:0];
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end
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'hD???: begin
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if (cycle_counter % 20 != 0) begin
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halt = 1;
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end else begin
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halt = 0;
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$display("HW : INSTR DRW Vx, Vy, nibble");
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x_cord = {24'h000000, registers[(opcode & 'h0F00) >> 8]};
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y_cord = {24'h000000, registers[(opcode & 'h00F0) >> 4]};
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x_cord %= 64;
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y_cord %= 32;
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scratch = (opcode & 'h000F);
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size = scratch[7:0];
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registers[15] = 0;
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for (r = 0; r < size; r++) begin
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for ( c = 0; c < 8; c++) begin
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if (r + y_cord >= 32 || x_cord + c >= 64)
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continue;
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screen_pixel = vram[((r + y_cord) * 64) + (x_cord + c)];
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sprite_pixel = memory[{16'h0000, index_reg} + r] & ('h80 >> c);
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if (|sprite_pixel) begin
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if (screen_pixel == 32'hFFFFFFFF) begin
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registers[15] = 1;
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end
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vram[((r + y_cord) * 64) + (x_cord + c)] ^= 32'hFFFFFFFF;
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end
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end
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end
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end
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end
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'hE?9E: begin
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$display("HW : INSTR SKP Vx");
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if (keyboard[{registers[(opcode & 'h0F00) >> 8]}[3:0]] == 1) begin
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program_counter += 2;
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end
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end
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'hE?A1: begin
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$display("HW : INSTR SNE Vx");
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if (keyboard[{registers[(opcode & 'h0F00) >> 8]}[3:0]] != 1) begin
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program_counter += 2;
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end
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end
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'hF?07: begin
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$display("HW : INSTR LD Vx, DT");
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registers[(opcode & 'h0F00) >> 8] = delay_timer;
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end
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'hF?0A: begin
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$display("HW : INSTR LD Vx, K");
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halt = 1;
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for(i = 0; i < 16; i++) begin
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if (watch_key == 255) begin
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if (keyboard[i]) begin
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watch_key = i;
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end
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end else begin
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if (!keyboard[watch_key]) begin
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halt = 0;
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watch_key = 255;
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end
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end
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end
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end
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'hF?15: begin
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$display("HW : INSTR LD DT, Vx");
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delay_timer = registers[(opcode & 'h0F00) >> 8];
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end
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'hF?18: begin
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$display("HW : INSTR LD ST, Vx");
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sound_timer = registers[(opcode & 'h0F00) >> 8];
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end
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'hF?1E: begin
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$display("HW : INSTR ADD I, Vx");
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index_reg = index_reg + {8'h00, registers[(opcode & 'h0F00) >> 8]};
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end
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'hF?33: begin
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$display("HW : INSTR LD B, Vx");
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scratch = {8'h00, registers[(opcode & 'h0F00) >> 8]};
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scratch2 = scratch % 10;
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memory[index_reg + 2] = scratch2[7:0];
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scratch /= 10;
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scratch2 = scratch % 10;
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memory[index_reg + 1] = scratch2[7:0];
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scratch /= 10;
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scratch2 = scratch % 10;
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memory[index_reg + 0] = scratch2[7:0];
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end
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'hF?55: begin
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$display("HW : INSTR LD [I], Vx");
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scratch = (opcode & 'h0F00) >> 8;
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for (i8 = 0; i8 <= scratch[7:0]; i8++) begin
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scratch2 = index_reg + {8'h00, i8};
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memory[scratch2[11:0]] = registers[i8[3:0]];
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end
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index_reg++;
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end
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'hF?65: begin
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$display("HW : INSTR LD Vx, [I]");
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scratch = (opcode & 'h0F00) >> 8;
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for (i8 = 0; i8 <= scratch[7:0]; i8++) begin
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scratch2 = index_reg + {8'h00, i8};
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registers[i8[3:0]] = memory[scratch2[11:0]];
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end
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index_reg++;
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end
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default: $display("HW : ILLEGAL INSTRUCTION");
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endcase
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if (!halt)
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program_counter += 2;
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cycle_counter++;
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end
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endmodule
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// pseudo random number generator
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module randomizer (
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input wire clk_in,
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input wire [15:0] pc,
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input bit keyboard [15:0],
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input int cycle_counter,
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output bit [7:0] rand_bit
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);
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bit [7:0] last;
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int i;
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always_ff @(posedge clk_in) begin
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for (i = 0; i < 8; i++) begin
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rand_bit[i] ^= ~keyboard[i] ? cycle_counter[i] : cycle_counter[7-i];
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rand_bit[i] ^= (cycle_counter % 7) == 0 ? pc[i] : ~pc[i];
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rand_bit[i] ^= keyboard[i+7] ? ~last[i] : last[i];
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end
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last = rand_bit;
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$display("Randomizer is: %b", rand_bit);
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end
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endmodule
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module chip8_gpu (
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input wire [31:0] vram [0:2047],
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input wire [7:0] sound_timer
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);
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import "DPI-C" function void draw_screen(logic [31:0] vram [0:2047], bit beep);
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always_comb begin
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draw_screen(vram, sound_timer > 0);
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end
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endmodule
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