Add CALL (untested) and ROM and internal RAM

[fpgaboy.git] / GBZ80Core.v

diff --git a/GBZ80Core.v b/GBZ80Core.v
index 338c2d7f3ea283261b7895adb96c2767b6f86770..cb231c2cfbc09eb684c6ae713416b6f3c63d230e 100644 (file)
--- a/GBZ80Core.v
+++ b/GBZ80Core.v
@@ -36,6 +36,7 @@
 `define INSN_NOP                               8'b00000000
 `define INSN_RST                               8'b11xxx111
 `define INSN_RET                               8'b110x1001     // 1 = RETI, 0 = RET
+`define INSN_CALL                              8'b11001101
 
 `define INSN_reg_A             3'b111
 `define INSN_reg_B             3'b000
@@ -80,7 +81,7 @@ module GBZ80Core(
        reg [7:0] rdata, wdata;         /* Read data from this bus cycle, or write data for the next. */
        reg rd = 1, wr = 0, newcycle = 1;
        
-       reg [7:0] tmp;                                  /* Generic temporary reg. */
+       reg [7:0] tmp, tmp2;                    /* Generic temporary regs. */
        
        reg [7:0] buswdata;
        assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
@@ -381,6 +382,34 @@ module GBZ80Core(
                                        end
                                endcase
                        end
+                       `INSN_CALL: begin
+                               case (cycle)
+                               0:      begin
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       end
+                               1:      begin
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       end
+                               2:      begin
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+                                               wdata <= registers[`REG_PCH];
+                                               wr <= 1;
+                                       end
+                               3:      begin
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+                                               wdata <= registers[`REG_PCL];
+                                               wr <= 1;
+                                       end
+                               4:      begin /* nothing happens on the bus next cycle! */ end
+                               5:      begin
+                                               `EXEC_NEWCYCLE; /* do NOT increment the PC */
+                                       end
+                               endcase
+                       end
                        default:
                                $stop;
                        endcase
@@ -638,6 +667,34 @@ module GBZ80Core(
                                        end
                                endcase
                        end
+                       `INSN_CALL: begin
+                               case (cycle)
+                               0:      cycle <= 1;
+                               1:      begin
+                                               cycle <= 2;
+                                               tmp <= rdata;   // tmp contains newpcl
+                                       end
+                               2:      begin
+                                               cycle <= 3;
+                                               tmp2 <= rdata;  // tmp2 contains newpch
+                                       end
+                               3: begin
+                                               cycle <= 4;
+                                               registers[`REG_PCH] <= tmp2;
+                                       end
+                               4: begin
+                                               cycle <= 5;
+                                               registers[`REG_PCL] <= tmp;
+                                       end
+                               5: begin
+                                               {registers[`REG_SPH],registers[`REG_SPL]} <=
+                                                       {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+                                               cycle <= 0;
+                                       end
+                               endcase
+                       end
+                       default:
+                               $stop;
                        endcase
                        state <= `STATE_FETCH;
                end
@@ -645,14 +702,53 @@ module GBZ80Core(
 endmodule
 
 `timescale 1ns / 1ps
+module ROM(
+       input [15:0] address,
+       inout [7:0] data,
+       input wr, rd);
+
+       reg [7:0] rom [2047:0];
+       initial $readmemh("rom.hex", rom);
+
+       wire decode = address[15:13] == 0;
+       reg [7:0] odata;
+       wire idata = data;
+       assign data = (rd && decode) ? odata : 8'bzzzzzzzz;
+       
+       always @(wr or rd)
+       begin
+               if (decode && rd)
+                       odata <= rom[address];
+       end
+endmodule
+
+module InternalRAM(
+       input [15:0] address,
+       inout [7:0] data,
+       input wr, rd);
+       
+       reg [7:0] ram [8191:0];
+       
+       wire decode = (address >= 16'hC000) && (address < 16'hFE00);
+       reg [7:0] odata;
+       wire idata = data;
+       assign data = (rd && decode) ? odata : 8'bzzzzzzzz;
+       
+       always @(rd or wr)
+       begin
+               if (decode && rd)
+                       odata <= ram[address];
+               else if (decode && wr)
+                       ram[address] <= idata;
+       end
+endmodule
+
 module TestBench();
        reg clk = 0;
        wire [15:0] addr;
        wire [7:0] data;
        wire wr, rd;
-       reg [7:0] rom [2047:0];
        
-       initial $readmemh("rom.hex", rom);
        always #10 clk <= ~clk;
        GBZ80Core core(
                .clk(clk),
@@ -660,5 +756,16 @@ module TestBench();
                .busdata(data),
                .buswr(wr),
                .busrd(rd));
-       assign data = rd ? rom[addr] : 8'bzzzzzzzz;
+       
+       ROM rom(
+               .address(addr),
+               .data(data),
+               .wr(wr),
+               .rd(rd));
+       
+       InternalRAM ram(
+               .address(addr),
+               .data(data),
+               .wr(wr),
+               .rd(rd));
 endmodule