///////////////////////////////////////////////////////////////////////////
//
// Filename:	cpuops.v
//
// Project:	Zip CPU -- a small, lightweight, RISC CPU soft core
//
// Purpose:	
//
// Creator:	Dan Gisselquist, Ph.D.
//		Gisselquist Tecnology, LLC
//
///////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2015, Gisselquist Technology, LLC
//
// This program is free software (firmware): you can redistribute it and/or
// modify it under the terms of  the GNU General Public License as published
// by the Free Software Foundation, either version 3 of the License, or (at
// your option) any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// for more details.
//
// License:	GPL, v3, as defined and found on www.gnu.org,
//		http://www.gnu.org/licenses/gpl.html
//
//
///////////////////////////////////////////////////////////////////////////
//
module	cpuops(i_clk, i_rst, i_ce, i_valid, i_op, i_a, i_b, o_c, o_f, o_valid);
	input		i_clk, i_rst, i_ce;
	input		[3:0]	i_op;
	input		[31:0]	i_a, i_b;
	input			i_valid;
	output	reg	[31:0]	o_c;
	output	wire	[3:0]	o_f;
	output	reg		o_valid;

	wire	[63:0]	w_rol_tmp;
	assign	w_rol_tmp = { i_a, i_a } << i_b[4:0];
	wire	[31:0]	w_rol_result;
	assign	w_rol_result = w_rol_tmp[63:32]; // Won't set flags

	wire	z, n, v;
	reg	c, pre_sign, set_ovfl;
	always @(posedge i_clk)
		if (i_ce)
			set_ovfl =((((i_op==4'h0)||(i_op==4'h8)) // SUB&CMP
						&&(i_a[31] != i_b[31]))
				||((i_op==4'ha)&&(i_a[31] == i_b[31])) // ADD
				||(i_op == 4'hd) // LSL
				||(i_op == 4'hf)); // LSR
	always @(posedge i_clk)
		if (i_ce)
		begin
			pre_sign <= (i_a[31]);
			c <= 1'b0;
			casez(i_op)
			4'b?000:{c,o_c } <= {(i_b>i_a),i_a - i_b};// CMP/SUB
			4'b?001:   o_c   <= i_a & i_b;		// BTST/And
			// 4'h4:   o_c   <= i_a[15:0] * i_b[15:0];
			4'h5:      o_c   <= w_rol_result;	// ROL
			4'h6:      o_c   <= { i_a[31:16], i_b[15:0] }; // LODILO
			4'h7:      o_c   <= { i_b[15:0], i_a[15:0] }; // LODIHI
			4'ha: { c, o_c } <= i_a + i_b;		// Add
			4'hb:      o_c   <= i_a | i_b;		// Or
			4'hc:      o_c   <= i_a ^ i_b;		// Xor
			4'hd: { c, o_c } <= (|i_b[31:5])? 33'h00 : {1'b0, i_a } << i_b[4:0];	// LSL
			4'he: { c, o_c } <= (|i_b[31:5])? {(33){i_a[31]}}:{ i_a[31],i_a}>> (i_b[4:0]);// ASR
			4'hf: { c, o_c } <= (|i_b[31:5])? 33'h00 : { 1'b0, i_a } >> (i_b[4:0]);// LSR
			default:   o_c   <=       i_b;		// MOV, LDI
			endcase
		end

	assign	z = (o_c == 32'h0000);
	assign	n = (o_c[31]);
	assign	v = (set_ovfl)&&(pre_sign != o_c[31]);

	assign	o_f = { v, n, c, z };

	initial	o_valid = 1'b0;
	always @(posedge i_clk)
		if (i_rst)
			o_valid <= 1'b0;
		else if (i_ce)
			o_valid <= i_valid;
		else if (~i_ce)
			o_valid <= 1'b0;
endmodule
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