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`timescale 10ns / 100ps

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

//

// Filename:    alttop.v

//

// Project:     CMod S6 System on a Chip, ZipCPU demonstration project

//

// Purpose:     This is an alternate toplevel configuration for the CMod S6

//              project.  Basically, the CMod S6 has so little logic within

//      it, that there's no logic available for in situ reprogramming.  This

//      toplevel file serves that purpose: It provides full configuration

//      access, via the UART port, for the flash (read and write), and full

//      test level access for all of the devices on the board.  What it

//      doesn't have, however, is the ZipCPU.  (I had to give up something to

//      get the logic back for this purpose!)

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

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

//

// Copyright (C) 2015-2016, 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

//

//

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

//

//

module alttop(i_clk_8mhz,

                o_qspi_cs_n, o_qspi_sck, io_qspi_dat,

                i_btn, o_led, o_pwm, o_pwm_shutdown_n, o_pwm_gain,

                        i_uart, o_uart, o_uart_rts_n, i_uart_cts_n,

                i_kp_row, o_kp_col,

                i_gpio, o_gpio,

                io_scl, io_sda,

                i_depp_astb_n, i_depp_dstb_n, i_depp_write_n, io_depp_data,

                        o_depp_wait

                );

        input           i_clk_8mhz;

        //

        // Quad SPI Flash

        output  wire            o_qspi_cs_n;

        output  wire            o_qspi_sck;

        inout   wire    [3:0]    io_qspi_dat;

        //

        // General purpose I/O

        input           [1:0]    i_btn;

        output  wire    [3:0]    o_led;

        output  wire            o_pwm, o_pwm_shutdown_n, o_pwm_gain;

        //

        // and our serial port

        input           i_uart;

        output  wire    o_uart;

        //      and it's associated control wires

        output  wire    o_uart_rts_n;

        input           i_uart_cts_n;

        // Our keypad

        input           [3:0]    i_kp_row;

        output  wire    [3:0]    o_kp_col;

        // and our GPIO

        input           [15:2]  i_gpio;

        output  wire    [15:2]  o_gpio;

        // and our I2C port

        inout                   io_scl, io_sda;

        // Finally, the DEPP interface ... if so enabled

        input                   i_depp_astb_n, i_depp_dstb_n, i_depp_write_n;

        inout           [7:0]    io_depp_data;

        output  wire    o_depp_wait;

        //

        // Clock management

        //

        //      Generate a usable clock for the rest of the board to run at.

        //

        wire    ck_zero_0, clk_s;

        // Clock frequency = (20 / 2) * 8Mhz = 80 MHz

        // Clock period = 12.5 ns

        DCM_SP #(

                .CLKDV_DIVIDE(2.0),

                .CLKFX_DIVIDE(2),               // Here's the divide by two

                .CLKFX_MULTIPLY(20),            // and here's the multiply by 20

                .CLKIN_DIVIDE_BY_2("FALSE"),

                .CLKIN_PERIOD(125.0),

                .CLKOUT_PHASE_SHIFT("NONE"),

                .CLK_FEEDBACK("1X"),

                .DESKEW_ADJUST("SYSTEM_SYNCHRONOUS"),

                .DLL_FREQUENCY_MODE("LOW"),

                .DUTY_CYCLE_CORRECTION("TRUE"),

                .PHASE_SHIFT(0),

                .STARTUP_WAIT("TRUE")

        ) u0(   .CLKIN(i_clk_8mhz),

                .CLK0(ck_zero_0),

                .CLKFB(ck_zero_0),

                .CLKFX(clk_s),

                .PSEN(1'b0),

                .RST(1'b0));

        //

        // The UART serial interface

        //

        //      Perhaps this should be part of our simulation model as well.

        //      For historical reasons, internal to Gisselquist Technology,

        //      this has remained separate from the simulation, allowing the

        //      simulation to bypass whether or not these two functions work.

        //

        wire            rx_stb, tx_stb;

        wire    [7:0]    rx_data, tx_data;

        wire            tx_busy;

        wire    [29:0]   uart_setup;

        // Baud rate is set by clock rate / baud rate desired.  Thus, 

        // 80 MHz / 9600 Baud = 8333, or about 0x208d.  We choose a slow

        // speed such as 9600 Baud to help the CPU keep up with the serial

        // port rate.

        localparam [30:0]        UART_SETUP = 31'h4000208d;

        assign  uart_setup = UART_SETUP;

        wire            reset_s;

        assign  reset_s = 1'b0;

        wire    rx_break, rx_parity_err, rx_frame_err, rx_ck_uart, tx_break;

        assign  tx_break = 1'b0;

        rxuart  #(UART_SETUP)

                rcvuart(clk_s, 1'b0, uart_setup,

                        i_uart, rx_stb, rx_data,

                        rx_break, rx_parity_err, rx_frame_err, rx_ck_uart);

        txuart  #(UART_SETUP)

                tcvuart(clk_s, reset_s, uart_setup, tx_break, tx_stb, tx_data,

                        i_uart_cts_n, o_uart, tx_busy);

        //

        // ALT-BUSMASTER

        //

        //      Busmaster is so named because it contains the wishbone

        //      interconnect that all of the internal devices are hung off of.

        //      To reconfigure this device for another purpose, usually

        //      the busmaster module (i.e. the interconnect) is all that needs

        //      to be changed: either to add more devices, or to remove them.

        //

        //      This is an alternate version of the busmaster interface,

        //      offering no ZipCPU and access to reprogramming via the flash.

        //

        wire    [3:0]    qspi_dat;

        wire    [1:0]    qspi_bmod;

        wire    [15:0]   w_gpio;

        wire    [7:0]    w_depp_data;

        wire    w_uart_rts_n;

`ifndef BYPASS_LOGIC

        altbusmaster    slavedbus(clk_s, 1'b0,

                // External ... bus control (if enabled)

                // DEPP I/O Control

                i_depp_astb_n, i_depp_dstb_n, i_depp_write_n,

                        io_depp_data, w_depp_data, o_depp_wait,

                // External UART interface

                rx_stb, rx_data, tx_stb, tx_data, tx_busy, w_uart_rts_n,

                // SPI/SD-card flash

                o_qspi_cs_n, o_qspi_sck, qspi_dat, io_qspi_dat, qspi_bmod,

                // Board lights and switches

                i_btn, o_led, o_pwm, { o_pwm_shutdown_n, o_pwm_gain },

                // Keypad connections

                i_kp_row, o_kp_col,

                // UART control

                uart_setup,

                // GPIO lines

                { i_gpio, io_scl, io_sda }, w_gpio

                );

        assign  o_uart_rts_n = (w_uart_rts_n);

        //

        // Quad SPI support

        //

        //      Supporting a Quad SPI port requires knowing which direction the

        //      wires are going at each instant, whether the device is in full

        //      Quad mode in, full quad mode out, or simply the normal SPI

        //      port with one wire in and one wire out.  This utilizes our

        //      control wires (qspi_bmod) to set the output lines appropriately.

        //

        assign io_qspi_dat = (~qspi_bmod[1])?({2'b11,1'bz,qspi_dat[0]})

                                :((qspi_bmod[0])?(4'bzzzz):(qspi_dat[3:0]));

`else

        reg     [26:0]   r_counter;

        always @(posedge clk_s)

                r_counter <= r_counter+1;

        assign  o_led[0] = r_counter[26];

        assign  o_led[1] = r_counter[25];

        assign  o_led[2] = r_counter[24];

        assign  o_led[3] = r_counter[23];

        // assign       o_led[0] = 1'b1;

        // assign       o_led[1] = 1'b0;

        // assign       o_led[2] = 1'b1;

        // assign       o_led[3] = 1'b0;

        assign  w_gpio = 16'h3;

        assign  o_pwm = 1'b0;

        assign  o_pwm_shutdown_n = 1'b0;

        assign  o_pwm_gain = 1'b0;

        assign  o_depp_wait = (~i_depp_astb_n);

        assign  w_depp_data = 8'h00;

        assign  io_qspi_dat = 4'bzzzz;

        assign  o_qspi_cs_n = 1'b1;

        assign  o_qspi_sck = 1'b1;

        assign  uart_setup = 30'h080002b6;

        assign  o_uart_rts_n = 1'b0;

`endif

        //

        // I2C support

        //

        //      Supporting I2C requires a couple quick adjustments to our

        //      GPIO lines.  Specifically, we'll allow that when the output

        //      (i.e. w_gpio) pins are high, then the I2C lines float.  They

        //      will be (need to be) pulled up by a resistor in order to 

        //      match the I2C protocol, but this change makes them look/act

        //      more like GPIO pins.

        //

        assign  io_sda = (w_gpio[0]) ? 1'bz : 1'b0;

        assign  io_scl = (w_gpio[1]) ? 1'bz : 1'b0;

        assign  o_gpio[15:2] = w_gpio[15:2];

        //

        // DEPP return data support

        //

        assign io_depp_data = (~i_depp_write_n)? 8'bzzzz_zzzz : w_depp_data;

endmodule