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////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
//
//
// Filename:    icontrol.v
// Filename:    icontrol.v
//
//
// Project:     Zip CPU -- a small, lightweight, RISC CPU soft core
// Project:     Zip CPU -- a small, lightweight, RISC CPU soft core
//
//
// Purpose:     An interrupt controller, for managing many interrupt sources.
// Purpose:     An interrupt controller, for managing many interrupt sources.
//
//
//      This interrupt controller started from the question of how best to
//      This interrupt controller started from the question of how best to
//      design a simple interrupt controller.  As such, it has a few nice
//      design a simple interrupt controller.  As such, it has a few nice
//      qualities to it:
//      qualities to it:
//              1. This is wishbone compliant
//              1. This is wishbone compliant
//              2. It sits on a 32-bit wishbone data bus
//              2. It sits on a 32-bit wishbone data bus
//              3. It only consumes one address on that wishbone bus.
//              3. It only consumes one address on that wishbone bus.
//              4. There is no extra delays associated with reading this
//              4. There is no extra delays associated with reading this
//                      device.
//                      device.
//              5. Common operations can all be done in one clock.
//              5. Common operations can all be done in one clock.
//
//
//      So, how shall this be used?  First, the 32-bit word is broken down as
//      So, how shall this be used?  First, the 32-bit word is broken down as
//      follows:
//      follows:
//
//
//      Bit 31  - This is the global interrupt enable bit.  If set, interrupts
//      Bit 31  - This is the global interrupt enable bit.  If set, interrupts
//              will be generated and passed on as they come in.
//              will be generated and passed on as they come in.
//      Bits 16-30      - These are specific interrupt enable lines.  If set,
//      Bits 16-30      - These are specific interrupt enable lines.  If set,
//              interrupts from source (bit#-16) will be enabled.
//              interrupts from source (bit#-16) will be enabled.
//              To set this line and enable interrupts from this source, write
//              To set this line and enable interrupts from this source, write
//              to the register with this bit set and the global enable set.
//              to the register with this bit set and the global enable set.
//              To disable this line, write to this register with global enable
//              To disable this line, write to this register with global enable
//              bit not set, but this bit set.  (Writing a zero to any of these
//              bit not set, but this bit set.  (Writing a zero to any of these
//              bits has no effect, either setting or unsetting them.)
//              bits has no effect, either setting or unsetting them.)
//      Bit 15 - This is the any interrupt pin.  If any interrupt is pending,
//      Bit 15 - This is the any interrupt pin.  If any interrupt is pending,
//              this bit will be set.
//              this bit will be set.
//      Bits 0-14       - These are interrupt bits.  When set, an interrupt is
//      Bits 0-14       - These are interrupt bits.  When set, an interrupt is
//              pending from the corresponding source--regardless of whether
//              pending from the corresponding source--regardless of whether
//              it was enabled.  (If not enabled, it won't generate an
//              it was enabled.  (If not enabled, it won't generate an
//              interrupt, but it will still register here.)  To clear any
//              interrupt, but it will still register here.)  To clear any
//              of these bits, write a '1' to the corresponding bit.  Writing
//              of these bits, write a '1' to the corresponding bit.  Writing
//              a zero to any of these bits has no effect.
//              a zero to any of these bits has no effect.
//
//
//      The peripheral also sports a parameter, IUSED, which can be set
//      The peripheral also sports a parameter, IUSED, which can be set
//      to any value between 1 and (buswidth/2-1, or) 15 inclusive.  This will
//      to any value between 1 and (buswidth/2-1, or) 15 inclusive.  This will
//      be the number of interrupts handled by this routine.  (Without the
//      be the number of interrupts handled by this routine.  (Without the
//      parameter, Vivado was complaining about unused bits.  With it, we can
//      parameter, Vivado was complaining about unused bits.  With it, we can
//      keep the complaints down and still use the routine).
//      keep the complaints down and still use the routine).
//
//
//      To get access to more than 15 interrupts, chain these together, so
//      To get access to more than 15 interrupts, chain these together, so
//      that one interrupt controller device feeds another.
//      that one interrupt controller device feeds another.
//
//
//
//
// Creator:     Dan Gisselquist, Ph.D.
// Creator:     Dan Gisselquist, Ph.D.
//              Gisselquist Technology, LLC
//              Gisselquist Technology, LLC
//
//
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
//
//
// Copyright (C) 2015,2017, Gisselquist Technology, LLC
// Copyright (C) 2015,2017-2019, Gisselquist Technology, LLC
//
//
// This program is free software (firmware): you can redistribute it and/or
// 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
// 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
// by the Free Software Foundation, either version 3 of the License, or (at
// your option) any later version.
// your option) any later version.
//
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// for more details.
// for more details.
//
//
// You should have received a copy of the GNU General Public License along
// 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
// 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
// target there if the PDF file isn't present.)  If not, see
// <http://www.gnu.org/licenses/> for a copy.
// <http://www.gnu.org/licenses/> for a copy.
//
//
// License:     GPL, v3, as defined and found on www.gnu.org,
// License:     GPL, v3, as defined and found on www.gnu.org,
//              http://www.gnu.org/licenses/gpl.html
//              http://www.gnu.org/licenses/gpl.html
//
//
//
//
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
//
//
//
//
module  icontrol(i_clk, i_reset, i_wr, i_proc_bus, o_proc_bus,
`default_nettype        none
 
//
 
module  icontrol(i_clk, i_reset, i_wr, i_data, o_data,
                i_brd_ints, o_interrupt);
                i_brd_ints, o_interrupt);
        parameter       IUSED = 15;
        parameter       IUSED = 15, BW=32;
        input                   i_clk, i_reset;
        input   wire            i_clk, i_reset;
        input                   i_wr;
        input   wire            i_wr;
        input           [31:0]   i_proc_bus;
        input   wire    [BW-1:0] i_data;
        output  wire    [31:0]   o_proc_bus;
        output  reg     [BW-1:0] o_data;
        input           [(IUSED-1):0]    i_brd_ints;
        input   wire    [(IUSED-1):0]    i_brd_ints;
        output  wire            o_interrupt;
        output  wire            o_interrupt;
 
 
        reg     [(IUSED-1):0]    r_int_state;
        reg     [(IUSED-1):0]    r_int_state;
        reg     [(IUSED-1):0]    r_int_enable;
        reg     [(IUSED-1):0]    r_int_enable;
        wire    [(IUSED-1):0]    nxt_int_state;
        wire    [(IUSED-1):0]    nxt_int_state;
        reg             r_any, r_interrupt, r_gie;
        reg             r_interrupt, r_gie;
 
        wire            w_any;
 
 
        assign  nxt_int_state = (r_int_state|i_brd_ints);
        assign  nxt_int_state = (r_int_state|i_brd_ints);
        initial r_int_state = 0;
        initial r_int_state = 0;
        always @(posedge i_clk)
        always @(posedge i_clk)
                if (i_reset)
                if (i_reset)
                        r_int_state  <= 0;
                        r_int_state  <= 0;
                else if (i_wr)
                else if (i_wr)
                        r_int_state <= nxt_int_state & (~i_proc_bus[(IUSED-1):0]);
                        r_int_state <= i_brd_ints | (r_int_state & (~i_data[(IUSED-1):0]));
                else
                else
                        r_int_state <= nxt_int_state;
                        r_int_state <= nxt_int_state;
        initial r_int_enable = 0;
        initial r_int_enable = 0;
        always @(posedge i_clk)
        always @(posedge i_clk)
                if (i_reset)
                if (i_reset)
                        r_int_enable <= 0;
                        r_int_enable <= 0;
                else if ((i_wr)&&(i_proc_bus[31]))
                else if ((i_wr)&&(i_data[BW-1]))
                        r_int_enable <= r_int_enable | i_proc_bus[(16+IUSED-1):16];
                        r_int_enable <= r_int_enable | i_data[(16+IUSED-1):16];
                else if ((i_wr)&&(~i_proc_bus[31]))
                else if ((i_wr)&&(!i_data[BW-1]))
                        r_int_enable <= r_int_enable & (~ i_proc_bus[(16+IUSED-1):16]);
                        r_int_enable <= r_int_enable & (~ i_data[(16+IUSED-1):16]);
 
 
        initial r_gie = 1'b0;
        initial r_gie = 1'b0;
        always @(posedge i_clk)
        always @(posedge i_clk)
                if (i_reset)
                if (i_reset)
                        r_gie <= 1'b0;
                        r_gie <= 1'b0;
                else if (i_wr)
                else if (i_wr)
                        r_gie <= i_proc_bus[31];
                        r_gie <= i_data[BW-1];
 
 
 
        assign  w_any = ((r_int_state & r_int_enable) != 0);
 
 
        initial r_any = 1'b0;
 
        always @(posedge i_clk)
 
                r_any <= ((r_int_state & r_int_enable) != 0);
 
        initial r_interrupt = 1'b0;
        initial r_interrupt = 1'b0;
        always @(posedge i_clk)
        always @(posedge i_clk)
                r_interrupt <= r_gie & r_any;
        if (i_reset)
 
                r_interrupt <= 1'b0;
 
        else
 
                r_interrupt <= (r_gie)&&(w_any);
 
 
        generate
        generate
        if (IUSED < 15)
        if (IUSED < 15)
        begin
        begin
                assign o_proc_bus = {
                always @(posedge i_clk)
 
                        o_data <= {
                                r_gie, { {(15-IUSED){1'b0}}, r_int_enable },
                                r_gie, { {(15-IUSED){1'b0}}, r_int_enable },
                                r_any, { {(15-IUSED){1'b0}}, r_int_state  } };
                                w_any, { {(15-IUSED){1'b0}}, r_int_state  } };
        end else begin
        end else begin
                assign o_proc_bus = { r_gie, r_int_enable, r_any, r_int_state };
                always @(posedge i_clk)
 
                        o_data <= { r_gie, r_int_enable, w_any, r_int_state };
        end endgenerate
        end endgenerate
 
 
        /*
 
        reg     int_condition;
 
        initial int_condition      = 1'b0;
 
        initial o_interrupt_strobe = 1'b0;
 
        always @(posedge i_clk)
 
                if (i_reset)
 
                begin
 
                        int_condition <= 1'b0;
 
                        o_interrupt_strobe <= 1'b0;
 
                end else if (~r_interrupt) // This might end up generating
 
                begin // many, many, (wild many) interrupts
 
                        int_condition <= 1'b0;
 
                        o_interrupt_strobe <= 1'b0;
 
                end else if ((~int_condition)&&(r_interrupt))
 
                begin
 
                        int_condition <= 1'b1;
 
                        o_interrupt_strobe <= 1'b1;
 
                end else
 
                        o_interrupt_strobe <= 1'b0;
 
        */
 
 
 
        assign  o_interrupt = r_interrupt;
        assign  o_interrupt = r_interrupt;
 
 
 
        // Make verilator happy
 
        // verilator lint_off UNUSED
 
        wire    [30:0]   unused;
 
        assign  unused = i_data[30:0];
 
        // verilator lint_on  UNUSED
 
 
 
`ifdef  FORMAL
 
`ifdef  ICONTROL
 
`define ASSUME  assume
 
`else
 
`define ASSUME  assert
 
`endif
 
 
 
        reg     f_past_valid;
 
 
 
        initial f_past_valid = 1'b0;
 
        always @(posedge i_clk)
 
                f_past_valid <= 1'b1;
 
 
 
        initial `ASSUME(i_reset);
 
        always @(*)
 
        if (!f_past_valid)
 
                `ASSUME(i_reset);
 
 
 
        always @(posedge i_clk)
 
        if ((!f_past_valid)||($past(i_reset)))
 
        begin
 
                assert(w_any == 0);
 
                assert(r_interrupt == 0);
 
                assert(r_gie == 0);
 
                assert(r_int_enable == 0);
 
        end
 
 
 
        always @(posedge i_clk)
 
        if ((f_past_valid)&&(!$past(i_reset)))
 
                assert((r_int_state & $past(i_brd_ints))==$past(i_brd_ints));
 
 
 
        always @(posedge i_clk)
 
        if (((f_past_valid)&&(!$past(i_reset)))
 
                        &&($past(r_int_state) & $past(r_int_enable))
 
                        &&($past(r_gie)) )
 
                assert(o_interrupt);
 
 
 
        always @(posedge i_clk)
 
        if ((f_past_valid)&&($past(w_any))&&(!$past(i_wr))&&(!$past(i_reset)))
 
                assert(w_any);
 
 
 
        always @(posedge i_clk)
 
        if ((f_past_valid)&&(!$past(r_gie)))
 
                assert(!o_interrupt);
 
 
 
        always @(posedge i_clk)
 
        if ((f_past_valid)&&(!$past(w_any)))
 
                assert(!o_interrupt);
 
 
 
        always @(posedge i_clk)
 
        if ((f_past_valid)&&(!$past(i_reset))&&($past(i_wr)))
 
        begin
 
                // Interrupts cannot be cleared, unless they are set
 
                assert(r_int_state == (($past(i_brd_ints))
 
                        |(($past(r_int_state))&(~$past(i_data[IUSED-1:0])))));
 
                assert(r_gie == $past(i_data[BW-1]));
 
        end else if ((f_past_valid)&&(!$past(i_reset)))
 
        begin
 
                assert(r_int_state == ($past(r_int_state)|$past(i_brd_ints)));
 
                assert(r_gie == $past(r_gie));
 
        end
 
 
 
`endif
endmodule
endmodule
 
 

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