X-Git-Url: http://git.joshuawise.com/fpgaboy.git/blobdiff_plain/3ad960bdb71efcbb1dfd436163085da0d70eb699..df770340caf8ecd26a55179484edb507082bd5c6:/insn_ret-retcc.v

diff --git a/insn_ret-retcc.v b/insn_ret-retcc.v
new file mode 100644
index 0000000..ef89003
--- /dev/null
+++ b/insn_ret-retcc.v
@@ -0,0 +1,48 @@
+`ifdef EXECUTE
+	`INSN_RET,`INSN_RETCC: begin
+		case (cycle)
+		0:	begin
+				rd <= 1;
+				address <= {registers[`REG_SPH],registers[`REG_SPL]};
+			end
+		1:	begin	// SPECIAL CASE: cycle does NOT increase linearly with ret!
+				`EXEC_INC_PC;	// cycle 1 is skipped if we are not retcc
+				case (opcode[4:3])
+				`INSN_cc_NZ:	if (registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+				`INSN_cc_Z:		if (~registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+				`INSN_cc_NC:	if (registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+				`INSN_cc_C:		if (~registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+				endcase
+				rd <= 1;
+				address <= {registers[`REG_SPH],registers[`REG_SPL]};
+			end
+		2:	begin
+				rd <= 1;
+				address <= {registers[`REG_SPH],registers[`REG_SPL]} + 1;
+			end
+		3:	begin /* twiddle thumbs */ end
+		4:	begin
+				`EXEC_NEWCYCLE;
+				// do NOT increment PC!
+			end
+		endcase
+	end
+`endif
+
+`ifdef WRITEBACK
+	`INSN_RET,`INSN_RETCC: begin
+		case (cycle)
+		0:	if (opcode[0])	// i.e., not RETCC
+				cycle <= 1;	// Skip cycle 1; it gets incremented on the next round.
+		1:	begin /* Nothing need happen here. */ end
+		2:	registers[`REG_PCL] <= rdata;
+		3:	registers[`REG_PCH] <= rdata;
+		4:	begin
+				{registers[`REG_SPH],registers[`REG_SPL]} <=
+					{registers[`REG_SPH],registers[`REG_SPL]} + 2;
+				if (opcode[4] && opcode[0])	/* RETI */
+					ie <= 1;
+			end
+		endcase
+	end
+`endif