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

//

// Filename:    fastmaster.v

//

// Project:     OpenArty, an entirely open SoC based upon the Arty platform

//

// Purpose:     On other projects, this file would be called the "bus

//              interconnect".  This module connects all the devices on the

//      Wishbone bus within this project together.  It is created by hand, not

//      automatically.

//

// 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

//

//

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

//

//

`define NO_ZIP_WBU_DELAY

// `define      ZIPCPU

`ifdef  ZIPCPU

//`define       ZIP_SYSTEM

`ifndef ZIP_SYSTEM

`define ZIP_BONES

`endif  // ZIP_SYSTEM

`endif  // ZipCPU

//

//

`define SDCARD_ACCESS

`define ETHERNET_ACCESS

`ifndef VERILATOR

`define ICAPE_ACCESS

`endif

`define FLASH_ACCESS

//`define       SDRAM_ACCESS

`define GPS_CLOCK

//      UART_ACCESS and GPS_UART have both been placed within fastio

//              `define UART_ACCESS

//              `define GPS_UART

`define RTC_ACCESS

`define OLEDRGB_ACCESS

//

// `define      CPU_SCOPE

// `define      GPS_SCOPE

`define FLASH_SCOPE

// `define      SDRAM_SCOPE

// `define      ENET_SCOPE

//

//

module  fastmaster(i_clk, i_rst,

                // CNC

                i_rx_stb, i_rx_data, o_tx_stb, o_tx_data, i_tx_busy,

                // Boad I/O

                i_sw, i_btn, o_led,

                o_clr_led0, o_clr_led1, o_clr_led2, o_clr_led3,

                // PMod I/O

                i_aux_rx, o_aux_tx, o_aux_cts, i_gps_rx, o_gps_tx,

                // The Quad SPI Flash

                o_qspi_cs_n, o_qspi_sck, o_qspi_dat, i_qspi_dat, o_qspi_mod,

                // The DDR3 SDRAM

                o_ddr_reset_n, o_ddr_cke,

                o_ddr_cs_n, o_ddr_ras_n, o_ddr_cas_n, o_ddr_we_n,

                o_ddr_dqs, o_ddr_addr, o_ddr_ba, o_ddr_data, i_ddr_data,

                // The SD Card

                o_sd_sck, o_sd_cmd, o_sd_data, i_sd_cmd, i_sd_data, i_sd_detect,

                // Ethernet control (MDIO) lines

                o_mdclk, o_mdio, o_mdwe, i_mdio,

                // OLED Control interface (roughly SPI)

                o_oled_sck, o_oled_cs_n, o_oled_mosi, o_oled_dcn,

                o_oled_reset_n, o_oled_vccen, o_oled_pmoden,

                // The GPS PMod

                i_gps_pps, i_gps_3df

                );

        parameter       ZA=24, ZIPINTS=13;

        input   i_clk, i_rst;

        // The bus commander, via an external uart port

        input                   i_rx_stb;

        input           [7:0]    i_rx_data;

        output  wire            o_tx_stb;

        output  wire    [7:0]    o_tx_data;

        input                   i_tx_busy;

        // I/O to/from board level devices

        input           [3:0]    i_sw;   // 16 switch bus

        input           [3:0]    i_btn;  // 5 Buttons

        output  wire    [3:0]    o_led;  // 16 wide LED's

        output  wire    [2:0]    o_clr_led0, o_clr_led1, o_clr_led2, o_clr_led3;

        // PMod UARTs

        input                   i_aux_rx;

        output  wire            o_aux_tx, o_aux_cts;

        input                   i_gps_rx;

        output  wire            o_gps_tx;

        // Quad-SPI flash control

        output  wire            o_qspi_cs_n, o_qspi_sck;

        output  wire    [3:0]    o_qspi_dat;

        input           [3:0]    i_qspi_dat;

        output  wire    [1:0]    o_qspi_mod;

        // DDR3 RAM controller

        output  wire            o_ddr_reset_n, o_ddr_cke,

                                o_ddr_cs_n, o_ddr_ras_n, o_ddr_cas_n,o_ddr_we_n;

        output  wire    [2:0]    o_ddr_dqs;

        output  wire    [13:0]   o_ddr_addr;

        output  wire    [2:0]    o_ddr_ba;

        output  wire    [31:0]   o_ddr_data;

        input           [31:0]   i_ddr_data;

        // The SD Card

        output  wire            o_sd_sck;

        output  wire            o_sd_cmd;

        output  wire    [3:0]    o_sd_data;

        input                   i_sd_cmd;

        input           [3:0]    i_sd_data;

        input                   i_sd_detect;

        // Ethernet control (MDIO)

        output  wire            o_mdclk, o_mdio, o_mdwe;

        input                   i_mdio;

        // OLEDRGB interface

        output  wire            o_oled_sck, o_oled_cs_n, o_oled_mosi,

                                o_oled_dcn, o_oled_reset_n, o_oled_vccen,

                                o_oled_pmoden;

        // GPS PMod (GPS UART above)

        input                   i_gps_pps;

        input                   i_gps_3df;

        //

        //

        // Master wishbone wires

        //

        //

        wire            wb_cyc, wb_stb, wb_we, wb_stall, wb_err;

        wire    [31:0]   wb_data, wb_addr;

        reg             wb_ack;

        reg     [31:0]   wb_idata;

        // Interrupts

        wire            gpio_int, oled_int, flash_int, scop_int;

        wire            enet_tx_int, enet_rx_int, sdcard_int, rtc_int, rtc_pps,

                        auxrx_int, auxtx_int, gpsrx_int, sw_int, btn_int;

        //

        //

        // First BUS master source: The UART

        //

        //

        wire    [31:0]   dwb_idata;

        // Wires going to devices

        wire            wbu_cyc, wbu_stb, wbu_we;

        wire    [31:0]   wbu_addr, wbu_data;

        // and then coming from devices

        wire            wbu_ack, wbu_stall, wbu_err;

        wire    [31:0]   wbu_idata;

        // And then headed back home

        wire    w_interrupt;

        // Oh, and the debug control for the ZIP CPU

        wire            wbu_zip_sel, zip_dbg_ack, zip_dbg_stall;

        wire    [31:0]   zip_dbg_data;

        wbubus  genbus(i_clk, i_rx_stb, i_rx_data,

                        wbu_cyc, wbu_stb, wbu_we, wbu_addr, wbu_data,

                        (wbu_zip_sel)?zip_dbg_ack:wbu_ack,

                        (wbu_zip_sel)?zip_dbg_stall:wbu_stall,

                                wbu_err,

                                (wbu_zip_sel)?zip_dbg_data:wbu_idata,

                        w_interrupt,

                        o_tx_stb, o_tx_data, i_tx_busy);

        // assign       o_dbg = (wbu_ack)&&(wbu_cyc);

        wire    zip_cpu_int; // True if the CPU suddenly halts

`ifdef  ZIPCPU

        // Are we trying to access the ZipCPU?  Such accesses must be special,

        // because they must succeed regardless of whether or not the ZipCPU

        // is on the bus.  Hence, we trap them here.

        assign  wbu_zip_sel = (wbu_addr[27]);

        //

        //

        // Second BUS master source: The ZipCPU

        //

        //

        wire            zip_cyc, zip_stb, zip_we;

        wire    [(ZA-1):0]       w_zip_addr;

        wire    [31:0]   zip_data, zip_scope_data;

        // and then coming from devices

        wire            zip_ack, zip_stall, zip_err;

`ifdef  ZIP_SYSTEM

        wire    [(ZIPINTS-1):0]  zip_interrupt_vec = {

                // Lazy(ier) interrupts

                oled_int, gpio_int, rtc_int, scop_int, flash_int, sw_int, btn_int,

                // Fast interrupts

                sdcard_int, auxtx_int, auxrx_int, enet_tx_int, enet_rx_int,

                        gpsrx_int, rtc_pps

                };

        zipsystem #(    .RESET_ADDRESS(24'h08000),

                        .ADDRESS_WIDTH(ZA),

                        .LGICACHE(10),

                        .START_HALTED(1),

                        .EXTERNAL_INTERRUPTS(ZIPINTS),

                        .HIGHSPEED_CPU(1))

                zippy(i_clk, i_rst,

                        // Zippys wishbone interface

                        zip_cyc, zip_stb, zip_we, w_zip_addr, zip_data,

                                zip_ack, zip_stall, dwb_idata, zip_err,

                        zip_interrupt_vec, zip_cpu_int,

                        // Debug wishbone interface

                        ((wbu_cyc)&&(wbu_zip_sel)),

                                ((wbu_stb)&&(wbu_zip_sel)),wbu_we, wbu_addr[0],

                                wbu_data,

                                zip_dbg_ack, zip_dbg_stall, zip_dbg_data

`ifdef  CPU_DEBUG

                        , zip_scope_data

`endif

                        );

`else // ZIP_SYSTEM

        wire    w_zip_cpu_int_ignored;

        zipbones #(     .RESET_ADDRESS(24'h08000),

                        .ADDRESS_WIDTH(ZA),

                        .LGICACHE(10),

                        .START_HALTED(1),

                        .HIGHSPEED_CPU(1))

                zippy(i_clk, i_rst,

                        // Zippys wishbone interface

                        zip_cyc, zip_stb, zip_we, w_zip_addr, zip_data,

                                zip_ack, zip_stall, dwb_idata, zip_err,

                        w_interrupt, w_zip_cpu_int_ignored,

                        // Debug wishbone interface

                        ((wbu_cyc)&&(wbu_zip_sel)),

                                ((wbu_stb)&&(wbu_zip_sel)),wbu_we, wbu_addr[0],

                                wbu_data,

                                zip_dbg_ack, zip_dbg_stall, zip_dbg_data

`ifdef  CPU_DEBUG

                        , zip_scope_data

`endif

                        );

        assign  zip_cpu_int = 1'b0;

`endif  // ZIP_SYSTEM v ZIP_BONES

        wire [31:0]      zip_addr;

        generate

        if (ZA < 32)

                assign  zip_addr = { {(32-ZA){1'b0}}, w_zip_addr};

        else

                assign  zip_addr = w_zip_addr;

        endgenerate

        //

        //

        // And an arbiter to decide who gets to access the bus

        //

        //

        wire    dwb_we, dwb_stb, dwb_cyc, dwb_ack, dwb_stall, dwb_err;

        wire    [31:0]   dwb_addr, dwb_odata;

        wbpriarbiter #(32,32) wbu_zip_arbiter(i_clk,

                // The ZIP CPU Master -- Gets the priority slot

                zip_cyc, zip_stb, zip_we, zip_addr, zip_data,

                        zip_ack, zip_stall, zip_err,

                // The UART interface Master

                (wbu_cyc)&&(~wbu_zip_sel), (wbu_stb)&&(~wbu_zip_sel), wbu_we,

                        wbu_addr, wbu_data,

                        wbu_ack, wbu_stall, wbu_err,

                // Common bus returns

                dwb_cyc, dwb_stb, dwb_we, dwb_addr, dwb_odata,

                        dwb_ack, dwb_stall, dwb_err);

        // 

        // 

        // And because the ZIP CPU and the Arbiter create an unacceptable

        // delay, we fail timing.  So we add in a delay cycle ...

        // 

        // 

        assign  wbu_idata = dwb_idata;

        busdelay        wbu_zip_delay(i_clk,

                        dwb_cyc, dwb_stb, dwb_we, dwb_addr, dwb_odata,

                                dwb_ack, dwb_stall, dwb_idata, dwb_err,

                        wb_cyc, wb_stb, wb_we, wb_addr, wb_data,

                                wb_ack, wb_stall, wb_idata, wb_err);

`else   // ZIPCPU

        assign  zip_cpu_int = 1'b0; // No CPU here to halt

        assign  wbu_zip_sel = 1'b0;

        // If there's no ZipCPU, there's no need for a Zip/WB-Uart bus delay.

        // We can go directly from the WB-Uart master bus to the master bus

        // itself.

        assign  wb_cyc    = wbu_cyc;

        assign  wb_stb    = wbu_stb;

        assign  wb_we     = wbu_we;

        assign  wb_addr   = wbu_addr;

        assign  wb_data   = wbu_data;

        assign  wbu_idata = wb_idata;

        assign  wbu_ack   = wb_ack;

        assign  wbu_stall = wb_stall;

        assign  wbu_err   = wb_err;

        // The CPU never halts if it doesn't exist, so set this interrupt to

        // zero.

        assign  zip_cpu_int= 1'b0;

`endif  // ZIPCPU

        //

        // Peripheral select lines.

        //

        // These lines will be true during any wishbone cycle whose address

        // line selects the given I/O peripheral.  The none_sel and many_sel

        // lines are used to detect problems, such as when no device is

        // selected or many devices are selected.  Such problems will lead to

        // bus errors (below).

        //

        wire    io_sel, scop_sel, netb_sel,

                        flctl_sel, rtc_sel, sdcard_sel, netp_sel,

                        oled_sel, gps_sel, mio_sel, cfg_sel,

                        mem_sel, flash_sel, ram_sel,

                        none_sel, many_sel;

        wire    [4:0]    skipaddr;

        assign  skipaddr = { wb_addr[26], wb_addr[22], wb_addr[15], wb_addr[11],

                                ~wb_addr[8] };

        assign  ram_sel   = (skipaddr[4]);

        assign  flash_sel = (skipaddr[4:3]==2'b01);

        assign  mem_sel   = (skipaddr[4:2]==3'b001);

        assign  netb_sel  = (skipaddr[4:1]==4'b0001);

        assign  io_sel    = (~|skipaddr)&&(wb_addr[7:5]==3'b000);

        assign  scop_sel  = (~|skipaddr)&&(wb_addr[7:3]==5'b00100);

        assign  rtc_sel   = (~|skipaddr)&&(wb_addr[7:2]==6'b001010);

        assign  sdcard_sel= (~|skipaddr)&&(wb_addr[7:2]==6'b001011);

        assign  netp_sel  = (~|skipaddr)&&(wb_addr[7:2]==6'b001101);

        assign  oled_sel  = (~|skipaddr)&&(wb_addr[7:2]==6'b001110);

        assign  gps_sel   = (~|skipaddr)&&(     (wb_addr[7:2]==6'b001100)

                                            ||  (wb_addr[7:3]==5'b01000));

        assign  mio_sel   = (~|skipaddr)&&(wb_addr[7:5]==3'b101);

        assign  flctl_sel = (~|skipaddr)&&(wb_addr[7:5]==3'b110);

        assign  cfg_sel   = (~|skipaddr)&&(wb_addr[7:5]==3'b111);

        wire    skiperr;

        assign  skiperr = (|wb_addr[31:27])

                                ||(~skipaddr[4])&&(|wb_addr[25:23])

                                ||(skipaddr[4:3]==2'b00)&&(|wb_addr[21:16])

                                ||(skipaddr[4:2]==3'b000)&&(|wb_addr[14:12])

                                ||(skipaddr[4:1]==4'b0000)&&(|wb_addr[10:9]);

        //

        // Peripheral acknowledgement lines

        //

        // These are only a touch more confusing, since the flash device will

        // ACK for both flctl_sel (the control line select), as well as the

        // flash_sel (the memory line select).  Hence we have one fewer ack

        // line.

        wire    io_ack, oled_ack,

                        rtc_ack, sdcard_ack,

                        netp_ack, gps_ack, mio_ack, cfg_ack, netb_ack,

                        mem_ack, flash_ack, ram_ack;

        reg     many_ack, slow_many_ack;

        reg     slow_ack, scop_ack;

        wire    [4:0]    ack_list;

        assign  ack_list = { ram_ack, flash_ack, mem_ack, netb_ack, cfg_ack };

        initial many_ack = 1'b0;

        always @(posedge i_clk)

                many_ack <= ((ack_list != 5'h10)

                        &&(ack_list != 5'h8)

                        &&(ack_list != 5'h4)

                        &&(ack_list != 5'h2)

                        &&(ack_list != 5'h1)

                        &&(ack_list != 5'h0));

        /*

        assign  many_ack = (    { 2'h0, ram_ack}

                                +{2'h0, flash_ack }

                                +{2'h0, mem_ack }

                                +{2'h0, netb_ack }

                                +{2'h0, slow_ack } > 3'h1 );

        */

        wire    [7:0] slow_ack_list;

        assign slow_ack_list = { mio_ack, gps_ack, netp_ack,

                        sdcard_ack, rtc_ack, scop_ack, oled_ack, io_ack };

        initial slow_many_ack = 1'b0;

        always @(posedge i_clk)

                slow_many_ack <= ((slow_ack_list != 8'h80)

                        &&(slow_ack_list != 8'h40)

                        &&(slow_ack_list != 8'h20)

                        &&(slow_ack_list != 8'h10)

                        &&(slow_ack_list != 8'h08)

                        &&(slow_ack_list != 8'h04)

                        &&(slow_ack_list != 8'h02)

                        &&(slow_ack_list != 8'h01)

                        &&(slow_ack_list != 8'h00));

        always @(posedge i_clk)

                wb_ack <= (wb_cyc)&&(|{ ram_ack, flash_ack, mem_ack,

                                netb_ack, cfg_ack, slow_ack });

        always @(posedge i_clk)

                slow_ack <= (wb_cyc)&&(|{oled_ack, mio_ack, gps_ack,

                                netp_ack, sdcard_ack, rtc_ack, scop_ack,

                                oled_ack, io_ack});

        //

        // Peripheral data lines

        //

        wire    [31:0]   io_data, oled_data,

                        rtc_data, sdcard_data,

                        netp_data, gps_data, mio_data, cfg_data, netb_data,

                        mem_data, flash_data, ram_data;

        reg     [31:0]   slow_data, scop_data;

        // 4 control lines, 5x32 data lines ... 

        always @(posedge i_clk)

                if ((ram_ack)||(flash_ack))

                        wb_idata <= (ram_ack)?ram_data:flash_data;

                else if ((mem_ack)||(netb_ack))

                        wb_idata <= (mem_ack)?mem_data:netb_data;

                else

                        wb_idata <= slow_data;

        // 7 control lines, 8x32 data lines

        always @(posedge i_clk)

                if ((cfg_ack)||(mio_ack))

                        slow_data <= (cfg_ack) ? cfg_data : mio_data;

                else if ((gps_ack)||(netp_ack))

                        slow_data <= (gps_ack) ? gps_data : netp_data;

                else if ((sdcard_ack)||(rtc_ack))

                        slow_data <= (sdcard_ack)?sdcard_data : rtc_data;

                else if ((scop_ack)|(oled_ack))

                        slow_data <= (scop_ack)?scop_data:oled_data;

                else

                        slow_data <= io_data;

        //

        // Peripheral stall lines

        //

        // As per the wishbone spec, these cannot be clocked or delayed.  They

        // *must* be done via combinatorial logic.

        //

        wire    io_stall, scop_stall, oled_stall,

                        rtc_stall, sdcard_stall,

                        netp_stall, gps_stall, mio_stall, cfg_stall, netb_stall,

                        mem_stall, flash_stall, ram_stall,

                        many_stall;

        assign  wb_stall = (wb_cyc)&&(

                        ((io_sel)&&(io_stall))          // Never stalls

                        ||((scop_sel)&&(scop_stall))    // Never stalls

                        ||((rtc_sel)&&(rtc_stall))      // Never stalls

                        ||((sdcard_sel)&&(sdcard_stall))// Never stalls

                        ||((netp_sel)&&(netp_stall))

                        ||((gps_sel)&&(gps_stall))      //(maybe? never stalls?)

                        ||((oled_sel)&&(oled_stall))

                        ||((mio_sel)&&(mio_stall))

                        ||((cfg_sel)&&(cfg_stall))

                        ||((netb_sel)&&(netb_stall))    // Never stalls

                        ||((mem_sel)&&(mem_stall))      // Never stalls

                        ||((flash_sel|flctl_sel)&&(flash_stall))

                        ||((ram_sel)&&(ram_stall)));

        //

        // Bus Error calculation(s)

        //

        // Selecting nothing is only an error if the strobe line is high as well

        // as the cycle line.  However, this is captured within the wb_err

        // logic itself, so we can ignore it for a line or two.

        assign  none_sel = ( //(skiperr)||

                                (~|{ io_sel, scop_sel, flctl_sel, rtc_sel,

                                        sdcard_sel, netp_sel, gps_sel,

                                        oled_sel,

                                        mio_sel, cfg_sel, netb_sel, mem_sel,

                                        flash_sel,ram_sel }));

        //

        // Selecting multiple devices at once is a design flaw that should

        // never happen.  Hence, if this logic won't build, we won't include

        // it.  Still, having this logic in place has saved my tush more than

        // once.

        //

        reg     [31:0]   sel_addr;

        always @(posedge i_clk)

                sel_addr <= wb_addr;

        reg     many_sel_a, many_sel_b, single_sel_a, single_sel_b, last_stb;

        always @(posedge i_clk)

        begin

                last_stb <= wb_stb;

                single_sel_a <= (wb_stb)&&((ram_sel)|(flash_sel)

                                        |(mem_sel)|(netb_sel)|(cfg_sel));

                many_sel_a <= 1'b0;

                if ((ram_sel)&&((flash_sel)||(mem_sel)||(netb_sel)||cfg_sel))

                        many_sel_a <= 1'b1;

                else if ((flash_sel)&&((mem_sel)||(netb_sel)||cfg_sel))

                        many_sel_a <= 1'b1;

                else if ((mem_sel)&&((netb_sel)||cfg_sel))

                        many_sel_a <= 1'b1;

                else if ((netb_sel)&&(cfg_sel))

                        many_sel_a <= 1'b1;

                single_sel_b <= (wb_stb)&&((mio_sel)||(gps_sel)||(netp_sel)

                                        ||(sdcard_sel)||(rtc_sel)||(flctl_sel)

                                        ||(oled_sel)||(scop_sel)||(io_sel));

                many_sel_b <= 1'b0;

                if ((mio_sel)&&((gps_sel)||(netp_sel)||(sdcard_sel)||(rtc_sel)

                                ||(flctl_sel)||(scop_sel)||(oled_sel)||(io_sel)))

                        many_sel_b <= 1'b1;

                else if ((gps_sel)&&((netp_sel)||(sdcard_sel)||(rtc_sel)

                                ||(flctl_sel)||(scop_sel)||(oled_sel)||(io_sel)))

                        many_sel_b <= 1'b1;

                else if ((netp_sel)&&((sdcard_sel)||(rtc_sel)

                                ||(flctl_sel)||(scop_sel)||(oled_sel)||(io_sel)))

                        many_sel_b <= 1'b1;

                else if ((sdcard_sel)&&((rtc_sel)

                                ||(flctl_sel)||(scop_sel)||(oled_sel)||(io_sel)))

                        many_sel_b <= 1'b1;

                else if ((rtc_sel)&&((flctl_sel)||(scop_sel)||(oled_sel)||(io_sel)))

                        many_sel_b <= 1'b1;

                else if ((flctl_sel)&&((scop_sel)||(oled_sel)||(io_sel)))

                        many_sel_b <= 1'b1;

                else if ((scop_sel)&&((oled_sel)||(io_sel)))

                        many_sel_b <= 1'b1;

                else if ((oled_sel)&&(io_sel))

                        many_sel_b <= 1'b1;

        end

        wire    sel_err; // 5 inputs

        assign  sel_err = ( (last_stb)&&(~single_sel_a)&&(~single_sel_b))

                                ||((single_sel_a)&&(single_sel_b))

                                ||((single_sel_a)&&(many_sel_a))

                                ||((single_sel_b)&&(many_sel_b));

        assign  wb_err = (wb_cyc)&&(sel_err || many_ack || slow_many_ack);

        // Finally, if we ever encounter a bus error, knowing the address of

        // the error will be important to figuring out how to fix it.  Hence,

        // we grab it here.  Be aware, however, that this might not truly be

        // the address that caused an error: in the case of none_sel it will

        // be, but if many_ack or slow_many_ack are true then we might just be

        // looking at an address on the bus that was nearby the one requested.

        reg     [31:0]   bus_err_addr;

        initial bus_err_addr = 32'h00;

        always @(posedge i_clk)

                if (wb_err)

                        bus_err_addr <= sel_addr;

        //

        // I/O peripheral

        //

        // The I/O processor, herein called an fastio.  This is a unique

        // set of peripherals--these are all of the peripherals that can answer

        // in a single clock--or, rather, they are the peripherals that can 

        // answer the bus before their clock.  Hence, the fastio simply consists

        // of a mux that selects between various peripheral responses.  Further,

        // these peripherals are not allowed to stall the bus.

        //

        // There is no option for turning these off--they will always be on.

        wire    [8:0]    master_ints;

        assign  master_ints = { zip_cpu_int, oled_int, rtc_int, sdcard_int,

                        enet_tx_int, enet_rx_int,

                        scop_int, flash_int, rtc_pps };

        wire    [5:0]    board_ints;

        wire    [3:0]    w_led;

        wire    rtc_ppd;

        fastio  #(

                .AUXUART_SETUP(30'hd50),

                .GPSUART_SETUP(30'hd20833)

                ) runio(i_clk, i_sw, i_btn,

                        w_led, o_clr_led0, o_clr_led1, o_clr_led2, o_clr_led3,

                        i_aux_rx, o_aux_tx, o_aux_cts, i_gps_rx, o_gps_tx,

                        wb_cyc, (io_sel)&&(wb_stb), wb_we, wb_addr[4:0],

                                wb_data, io_ack, io_stall, io_data,

                        rtc_ppd,

                        bus_err_addr, master_ints, w_interrupt,

                        board_ints);

        assign  { gpio_int, auxrx_int, auxtx_int, gpsrx_int, sw_int, btn_int } = board_ints;

        /*

        reg     [25:0]  dbg_counter_err, dbg_counter_cyc, dbg_counter_sel,

                        dbg_counter_many;

        // assign wb_err = (wb_cyc)&&(sel_err || many_ack || slow_many_ack);

        always @(posedge i_clk)

                if (wbu_cyc)

                        dbg_counter_cyc <= 0;

                else if (!dbg_counter_cyc[25])

                        dbg_counter_cyc <= dbg_counter_cyc+26'h1;

        always @(posedge i_clk)

                if (wbu_err)

                        dbg_counter_err <= 0;