X-Git-Url: http://git.joshuawise.com/fpgaboy.git/blobdiff_plain/77ab69d7bb0902e6ebf0994159ed2205f8413e34..b057a5d6e6db6db06ae33703ca72cd235eec91d6:/core/insn_ret-retcc.v

diff --git a/core/insn_ret-retcc.v b/core/insn_ret-retcc.v
new file mode 100644
index 0000000..dab27c3
--- /dev/null
+++ b/core/insn_ret-retcc.v
@@ -0,0 +1,37 @@
+`ifdef EXECUTE
+	`INSN_RET,`INSN_RETCC: begin
+		case (cycle)
+		0:	`EXEC_READ(`_SP)
+		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 (`_F[7])  `EXEC_NEWCYCLE
+				`INSN_cc_Z:	if (~`_F[7]) `EXEC_NEWCYCLE
+				`INSN_cc_NC:	if (`_F[4])  `EXEC_NEWCYCLE
+				`INSN_cc_C:	if (~`_F[4]) `EXEC_NEWCYCLE
+				endcase
+				`EXEC_READ(`_SP)	// retry the read
+			end
+		2:	`EXEC_READ(`_SP + 1)
+		3:	begin /* twiddle thumbs */ end
+		4:	`EXEC_NEWCYCLE
+		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:	`_PCL <= rdata;
+		3:	`_PCH <= rdata;
+		4:	begin
+				`_SP <= `_SP + 2;
+				if (opcode[4] && opcode[0])	/* RETI */
+					ie <= 1;
+			end
+		endcase
+	end
+`endif