Implement JR CC, $nn

rtl/cpu/control.sv

@@ -8,6 +8,8 @@ module control (
 
     input  logic [ 7:0] rdata_i,
 
+    input  logic [ 7:0] f_i,
+
     output state_t state_o,
 
     output logic [15:0] pc_o,
@@ -74,8 +76,12 @@ module control (
     logic        is_undef;
     logic        pc_incr;
     logic        instr_valid;
+    logic        branch_taken;
+    logic        branch_cc_true;
 
     sp_src_t     sp_src;
+    pc_src_t     pc_src;
+    cc_t         cc;
 
     always_ff @(posedge clk_i) begin
         nreset_r <= nreset_i;
@@ -89,8 +95,9 @@ module control (
     `DEF_FF(operand0_r, operand0_next, operand0_we, '0);
     `DEF_FF(operand1_r, operand1_next, operand1_we, '0);
 
-    assign pc_we   = nreset_r & pc_incr & ~is_undef;
+    assign pc_we   = (nreset_r & pc_incr & ~is_undef) | branch_taken;
-    assign pc_next = (pc_r + 16'b1);
+    assign pc_next = (branch_taken & pc_src == PC_SRC_OPERAND8) ? (pc_r + {{8{operand0_r[7]}}, operand0_r}) :
+                                                                  (pc_r + 16'b1);
 
     assign sp_next = (sp_src == SP_SRC_OPERAND16) ? {operand1_r, operand0_r} : '0;
 
@@ -145,7 +152,9 @@ module control (
         .reg16_dest_o  (reg16_dest_o),
 
         .memory_we_o   (decoder_memory_we),
-        .adr_src_o     (decoder_adr_src)
+        .adr_src_o     (decoder_adr_src),
+        .cc_o          (cc),
+        .pc_src_o      (pc_src)
     );
 
     assign decoder_instr0_selected = (state_r == ST1_DEC)  ? rdata_i : instr_r;
@@ -157,6 +166,12 @@ module control (
 
     assign pc_incr = (state_r == ST0_ADDR) | (state_r == ST1_DEC & decoder_need_instr1) | (state_r == ST2_DEC & decoder_need_instr2);
 
+    assign branch_taken = instr_valid & (pc_src != PC_SRC_SEQ) & branch_cc_true;
+    assign branch_cc_true = ((cc == CC_NZ) & ~f_i[7]) |
+                            ((cc == CC_Z)  &  f_i[7]) |
+                            ((cc == CC_NC) & ~f_i[4]) |
+                            ((cc == CC_C)  &  f_i[4]);
+
     assign state_o = state_r;
     assign pc_o    = pc_r;
     assign sp_o    = sp_r;

rtl/cpu/cpu.sv

@@ -55,6 +55,7 @@ module cpu (
         .nreset_i      (nreset_i),
         .rdata_i       (rdata_i),
         .state_o       (state),
+        .f_i           (regf),
         .pc_o          (pc),
         .sp_o          (sp),
         .alu_op_valid_o(alu_op_valid),

rtl/cpu/cpu_pkg.svh

@@ -32,6 +32,13 @@ package cpu_pkg;
         REG16_SP_AF = 2'h03
     } reg16_t;
 
+    typedef enum logic [1:0] {
+        CC_NZ = 2'h00,
+        CC_Z  = 2'h01,
+        CC_NC = 2'h02,
+        CC_C  = 2'h03
+    } cc_t;
+
     typedef enum logic [3:0] {
         ALU_OP_ADD = 4'h00,
         ALU_OP_ADC = 4'h01,
@@ -72,6 +79,11 @@ package cpu_pkg;
         ADR_SRC_HL
     } adr_src_t;
 
+    typedef enum {
+        PC_SRC_SEQ,
+        PC_SRC_OPERAND8
+    } pc_src_t;
+
 endpackage
 
 `define DEF_FF(register, next, we, rst_value) \

rtl/cpu/decode.sv

@@ -26,6 +26,9 @@ module decode (
     output reg16_t     reg16_dest_o,
     output reg16_t     reg16_src_o,
 
+    output cc_t        cc_o,
+
+    output pc_src_t    pc_src_o,
     output adr_src_t   adr_src_o,
     output logic       memory_we_o
 );
@@ -42,6 +45,7 @@ module decode (
     logic is_ldd_hl_a;
     logic is_alu_a_r;
     logic is_bit_n_r;
+    logic is_jr_cc_n;
 
     reg8_t reg8_src;
 
@@ -60,15 +64,16 @@ module decode (
     assign is_alu_a_r = (dec_x == 3'h2);
     assign is_bit_n_r = (is_cb & instr1_i[7:6] == 2'h1);
 
+    assign is_jr_cc_n = (dec_x == 2'h0) & (dec_z == 2'h0) & dec_y[2];
 
     assign reg8_src = is_cb ? reg8_t'(instr1_i[2:0]) :
                               reg8_t'(dec_z);
 
 
-    assign need_instr1_o = is_ld_sp_nnnn | is_ld_rr_nnnn | is_cb;
+    assign need_instr1_o = is_ld_sp_nnnn | is_ld_rr_nnnn | is_cb | is_jr_cc_n;
     assign need_instr2_o = is_ld_sp_nnnn | is_ld_rr_nnnn;
 
-    assign undef_o = ~(is_ld_sp_nnnn | is_ld_rr_nnnn | is_alu_a_r | is_ldd_hl_a | is_bit_n_r);
+    assign undef_o = ~(is_ld_sp_nnnn | is_ld_rr_nnnn | is_alu_a_r | is_ldd_hl_a | is_bit_n_r | is_jr_cc_n);
 
     assign sp_we_o  = is_ld_sp_nnnn & (state_i == ST4_EXEC);
 
@@ -91,9 +96,14 @@ module decode (
     assign reg16_src_o  = is_ldd_hl_a ? REG16_HL : reg16_t'(dec_p);
     assign reg16_dest_o = is_ldd_hl_a ? REG16_HL : reg16_t'(dec_p);
 
+    assign pc_src_o = is_jr_cc_n ? PC_SRC_OPERAND8 :
+                                   PC_SRC_SEQ;
+
     assign adr_src_o = is_ldd_hl_a ? ADR_SRC_HL :
                                      ADR_SRC_PC;
 
+    assign cc_o = cc_t'(dec_y[1:0]);
+
     assign memory_we_o = is_ldd_hl_a;
 
 endmodule : decode