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////////////////////////////////////////////////////////////////////////////////

//

// Filename:    zipbones.v

//

// Project:     Zip CPU -- a small, lightweight, RISC CPU soft core

//

// Purpose:     In the spirit of keeping the Zip CPU small, this implements a

//              Zip System with no peripherals: Any peripherals you wish will

//              need to be implemented off-module.

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

////////////////////////////////////////////////////////////////////////////////

//

// Copyright (C) 2015, 2017, 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.

//

// You should have received a copy of the GNU General Public License along

// with this program.  (It's in the $(ROOT)/doc directory, run make with no

// target there if the PDF file isn't present.)  If not, see

// <http://www.gnu.org/licenses/> for a copy.

//

// License:     GPL, v3, as defined and found on www.gnu.org,

//              http://www.gnu.org/licenses/gpl.html

//

//

////////////////////////////////////////////////////////////////////////////////

//

//

`include "cpudefs.v"

//

module  zipbones(i_clk, i_rst,

                // Wishbone master interface from the CPU

                o_wb_cyc, o_wb_stb, o_wb_we, o_wb_addr, o_wb_data, o_wb_sel,

                        i_wb_ack, i_wb_stall, i_wb_data, i_wb_err,

                // Incoming interrupts

                i_ext_int,

                // Our one outgoing interrupt

                o_ext_int,

                // Wishbone slave interface for debugging purposes

                i_dbg_cyc, i_dbg_stb, i_dbg_we, i_dbg_addr, i_dbg_data,

                        o_dbg_ack, o_dbg_stall, o_dbg_data

`ifdef  DEBUG_SCOPE

                , o_zip_debug

`endif

                );

        parameter       RESET_ADDRESS=32'h0100000, ADDRESS_WIDTH=30,

                        LGICACHE=8, START_HALTED=0;

        localparam      AW=ADDRESS_WIDTH;

        input   i_clk, i_rst;

        // Wishbone master

        output  wire            o_wb_cyc, o_wb_stb, o_wb_we;

        output  wire    [(AW-1):0]       o_wb_addr;

        output  wire    [31:0]   o_wb_data;

        output  wire    [3:0]    o_wb_sel;

        input                   i_wb_ack, i_wb_stall;

        input           [31:0]   i_wb_data;

        input                   i_wb_err;

        // Incoming interrupts

        input                   i_ext_int;

        // Outgoing interrupt

        output  wire            o_ext_int;

        // Wishbone slave

        input                   i_dbg_cyc, i_dbg_stb, i_dbg_we, i_dbg_addr;

        input           [31:0]   i_dbg_data;

        output  reg             o_dbg_ack;

        output  wire            o_dbg_stall;

        output  wire    [31:0]   o_dbg_data;

        //

`ifdef  DEBUG_SCOPE

        output  wire    [31:0]   o_zip_debug;

`endif

        // 

        //

        //

        wire    sys_cyc, sys_stb, sys_we;

        wire    [4:0]    sys_addr;

        wire    [(AW-1):0]       cpu_addr;

        wire    [31:0]   sys_data;

        wire            sys_ack, sys_stall;

        //

        // The external debug interface

        //

        // We offer only a limited interface here, requiring a pre-register

        // write to set the local address.  This interface allows access to

        // the Zip System on a debug basis only, and not to the rest of the

        // wishbone bus.  Further, to access these registers, the control

        // register must first be accessed to both stop the CPU and to 

        // set the following address in question.  Hence all accesses require

        // two accesses: write the address to the control register (and halt

        // the CPU if not halted), then read/write the data from the data

        // register.

        //

        wire            cpu_break, dbg_cmd_write;

        reg             cmd_reset, cmd_halt, cmd_step, cmd_clear_pf_cache;

        reg     [4:0]    cmd_addr;

        wire    [3:0]    cpu_dbg_cc;

        assign  dbg_cmd_write = (i_dbg_cyc)&&(i_dbg_stb)&&(i_dbg_we)&&(~i_dbg_addr);

        //

        // Always start us off with an initial reset

        //

        initial cmd_reset = 1'b1;

        always @(posedge i_clk)

                cmd_reset <= ((dbg_cmd_write)&&(i_dbg_data[6]));

        //

        initial cmd_halt  = START_HALTED;

        always @(posedge i_clk)

                if (i_rst)

                        cmd_halt <= (START_HALTED == 1)? 1'b1 : 1'b0;

                else if (dbg_cmd_write)

                        cmd_halt <= ((i_dbg_data[10])||(i_dbg_data[8]));

                else if ((cmd_step)||(cpu_break))

                        cmd_halt  <= 1'b1;

        initial cmd_clear_pf_cache = 1'b0;

        always @(posedge i_clk)

                if (i_rst)

                        cmd_clear_pf_cache <= 1'b0;

                else if (dbg_cmd_write)

                        cmd_clear_pf_cache <= i_dbg_data[11];

                else

                        cmd_clear_pf_cache <= 1'b0;

        //

        initial cmd_step  = 1'b0;

        always @(posedge i_clk)

                cmd_step <= (dbg_cmd_write)&&(i_dbg_data[8]);

        //

        initial cmd_addr = 5'h0;

        always @(posedge i_clk)

                if (dbg_cmd_write)

                        cmd_addr <= i_dbg_data[4:0];

        wire    cpu_reset;

        assign  cpu_reset = (cmd_reset)||(i_rst);

        wire    cpu_halt, cpu_dbg_stall;

        assign  cpu_halt = (i_rst)||((cmd_halt)&&(~cmd_step));

        wire    [31:0]   cmd_data;

        // Values:

        //      0x0003f -> cmd_addr mask

        //      0x00040 -> reset

        //      0x00080 -> PIC interrrupts enabled

        //      0x00100 -> cmd_step

        //      0x00200 -> cmd_stall

        //      0x00400 -> cmd_halt

        //      0x00800 -> cmd_clear_pf_cache

        //      0x01000 -> cc.sleep

        //      0x02000 -> cc.gie

        //      0x10000 -> External interrupt line is high

        assign  cmd_data = { 7'h00, 8'h00, i_ext_int,

                        cpu_dbg_cc,

                        1'b0, cmd_halt, (~cpu_dbg_stall), 1'b0,

                        1'b0, cpu_reset, 1'b0, cmd_addr };

        //

        // The CPU itself

        //

        wire            cpu_gbl_stb, cpu_lcl_cyc, cpu_lcl_stb,

                        cpu_we, cpu_dbg_we,

                        cpu_op_stall, cpu_pf_stall, cpu_i_count;

        wire    [31:0]   cpu_data;

        wire    [31:0]   cpu_dbg_data;

        assign cpu_dbg_we = ((i_dbg_cyc)&&(i_dbg_stb)

                                        &&(i_dbg_we)&&(i_dbg_addr));

        zipcpu  #(.RESET_ADDRESS(RESET_ADDRESS),

                        .ADDRESS_WIDTH(ADDRESS_WIDTH),

                        .LGICACHE(LGICACHE),

                        .WITH_LOCAL_BUS(0))

                thecpu(i_clk, cpu_reset, i_ext_int,

                        cpu_halt, cmd_clear_pf_cache, cmd_addr[4:0], cpu_dbg_we,

                                i_dbg_data, cpu_dbg_stall, cpu_dbg_data,

                                cpu_dbg_cc, cpu_break,

                        o_wb_cyc, o_wb_stb,

                                cpu_lcl_cyc, cpu_lcl_stb,

                                o_wb_we, o_wb_addr, o_wb_data, o_wb_sel,

                                i_wb_ack, i_wb_stall, i_wb_data,

                                (i_wb_err)||(cpu_lcl_cyc),

                        cpu_op_stall, cpu_pf_stall, cpu_i_count

`ifdef  DEBUG_SCOPE

                        , o_zip_debug

`endif

                        );

        // Return debug response values

        assign  o_dbg_data = (~i_dbg_addr)?cmd_data :cpu_dbg_data;

        initial o_dbg_ack = 1'b0;

        always @(posedge i_clk)

                o_dbg_ack <= (i_dbg_cyc)&&((~i_dbg_addr)||(~o_dbg_stall));

        assign  o_dbg_stall=(i_dbg_cyc)&&(cpu_dbg_stall)&&(i_dbg_addr);

        assign  o_ext_int = (cmd_halt) && (~i_wb_stall);

endmodule