Cut 1 at interrupt support for CPU

[fpgaboy.git] / GBZ80Core.v

diff --git a/GBZ80Core.v b/GBZ80Core.v
index 095d9e85e555d592bcdcca33ae6f23bee3ca663d..57c22d20e27188d7f633bb66a1f74189ca8ebfbd 100644 (file)
--- a/GBZ80Core.v
+++ b/GBZ80Core.v
@@ -46,6 +46,9 @@
 `define INSN_JR_imm                    8'b00011000
 `define INSN_JRCC_imm          8'b001xx000
 `define INSN_INCDEC16          8'b00xxx011
+`define INSN_VOP_INTR          8'b11111100     // 0xFC is grabbed by the fetch if there is an interrupt pending.
+`define INSN_DI                                8'b11110011
+`define INSN_EI                                8'b11111011
 
 `define INSN_cc_NZ                     2'b00
 `define INSN_cc_Z                              2'b01
@@ -89,7 +92,8 @@ module GBZ80Core(
        input clk,
        output reg [15:0] busaddress = 0,       /* BUS_* is latched on STATE_FETCH. */
        inout [7:0] busdata,
-       output reg buswr = 0, output reg busrd = 0);
+       output reg buswr = 0, output reg busrd = 0,
+       input irq, input [7:0] jaddr);
        
        reg [1:0] state = 0;                                    /* State within this bus cycle (see STATE_*). */
        reg [2:0] cycle = 0;                                    /* Cycle for instructions. */
@@ -108,7 +112,7 @@ module GBZ80Core(
        reg [7:0] buswdata;
        assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
        
-       reg ie = 0;
+       reg ie = 0, iedelay = 0;
        
        initial begin
                registers[ 0] <= 0;
@@ -129,6 +133,10 @@ module GBZ80Core(
                newcycle <= 1;
                state <= 0;
                cycle <= 0;
+               busrd <= 0;
+               buswr <= 0;
+               busaddress <= 0;
+               iedelay <= 0;
        end
 
        always @(posedge clk)
@@ -149,7 +157,10 @@ module GBZ80Core(
                end
                `STATE_DECODE: begin
                        if (newcycle) begin
-                               opcode <= busdata;
+                               if (ie && irq)
+                                       opcode <= `INSN_VOP_INTR;
+                               else
+                                       opcode <= busdata;
                                rdata <= busdata;
                                newcycle <= 0;
                                cycle <= 0;
@@ -157,6 +168,10 @@ module GBZ80Core(
                                if (rd) rdata <= busdata;
                                cycle <= cycle + 1;
                        end
+                       if (iedelay) begin
+                               ie <= 1;
+                               iedelay <= 0;
+                       end
                        buswr <= 0;
                        busrd <= 0;
                        wr <= 0;
@@ -552,6 +567,31 @@ module GBZ80Core(
                                        end
                                endcase
                        end
+                       `INSN_VOP_INTR: begin
+                               case (cycle)
+                               0:      begin
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+                                               wdata <= registers[`REG_PCH];
+                                               wr <= 1;
+                                       end
+                               1:      begin
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+                                               wdata <= registers[`REG_PCL];
+                                               wr <= 1;
+                                       end
+                               2:      begin
+                                               `EXEC_NEWCYCLE;
+                                       end
+                               endcase
+                       end
+                       `INSN_DI: begin
+                               `EXEC_NEWCYCLE;
+                               `EXEC_INC_PC;
+                       end
+                       `INSN_EI: begin
+                               `EXEC_NEWCYCLE;
+                               `EXEC_INC_PC;
+                       end
                        default:
                                $stop;
                        endcase
@@ -896,6 +936,20 @@ module GBZ80Core(
                                        end
                                endcase
                        end
+                       `INSN_VOP_INTR: begin
+                               case (cycle)
+                               0:      begin end
+                               1:      {registers[`REG_SPH],registers[`REG_SPL]}
+                                               <= {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+                               2:      begin
+                                               ie <= 0;
+                                               {registers[`REG_PCH],registers[`REG_PCL]} <=
+                                                       {8'b0,jaddr};
+                                       end
+                               endcase
+                       end
+                       `INSN_DI: ie <= 0;
+                       `INSN_EI: iedelay <= 1;
                        default:
                                $stop;
                        endcase