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

//

// Filename:    wbdmac.v

//

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

//

// Purpose:     Wishbone DMA controller

//

//      This module is controllable via the wishbone, and moves values from

//      one location in the wishbone address space to another.  The amount of

//      memory moved at any given time can be up to 4kB, or equivalently 1kW.

//      Four registers control this DMA controller: a control/status register,

//      a length register, a source WB address and a destination WB address.

//      These register may be read at any time, but they may only be written

//      to when the controller is idle.

//

//      The meanings of three of the setup registers should be self explanatory:

//              - The length register controls the total number of words to

//                      transfer.

//              - The source address register controls where the DMA controller

//                      reads from.  This address may or may not be incremented

//                      after each read, depending upon the setting in the

//                      control/status register.

//              - The destination address register, which controls where the DMA

//                      controller writes to.  This address may or may not be

//                      incremented after each write, also depending upon the

//                      setting in the control/status register.

//

//      It is the control/status register, at local address zero, that needs

//      more definition:

//

//      Bits:

//      31      R       Write protect   If this is set to one, it means the

//                              write protect bit is set and the controller

//                              is therefore idle.  This bit will be set upon

//                              completing any transfer.

//      30      R       Error.          The controller stopped mid-transfer

//                                      after receiving a bus error.

//      29      R/W     inc_s_n         If set to one, the source address

//                              will not increment from one read to the next.

//      28      R/W     inc_d_n         If set to one, the destination address

//                              will not increment from one write to the next.

//      27      R       Always 0

//      26..16  R       nread           Indicates how many words have been read,

//                              and not necessarily written (yet).  This

//                              combined with the cfg_len parameter should tell

//                              exactly where the controller is at mid-transfer.

//      27..16  W       WriteProtect    When a 12'h3db is written to these

//                              bits, the write protect bit will be cleared.

//                              

//      15      R/W     on_dev_trigger  When set to '1', the controller will

//                              wait for an external interrupt before starting.

//      14..10  R/W     device_id       This determines which external interrupt

//                              will trigger a transfer.

//      9..0    R/W     transfer_len    How many bytes to transfer at one time.

//                              The minimum transfer length is one, while zero

//                              is mapped to a transfer length of 1kW.

//

//      Write 32'hffed00 to halt an ongoing transaction, completing anything

//      remaining, or 32'hafed00 to abort the current transaction leaving

//      any unfinished read/write in an undetermined state.

//

//

//      To use this, follow this checklist:

//      1. Wait for any prior DMA operation to complete

//              (Read address 0, wait 'till either top bit is set or cfg_len==0)

//      2. Write values into length, source and destination address. 

//              (writei(3, &vals) should be sufficient for this.)

//      3. Enable the DMAC interrupt in whatever interrupt controller is present

//              on the system.

//      4. Write the final start command to the setup/control/status register:

//              Set inc_s_n, inc_d_n, on_dev_trigger, dev_trigger,

//                      appropriately for your task

//              Write 12'h3db to the upper word.

//              Set the lower word to either all zeros, or a smaller transfer

//              length if desired.

//      5. wait() for the interrupt and the operation to complete.

//              Prior to completion, number of items successfully transferred

//              be read from the length register.  If the internal buffer is

//              being used, then you can read how much has been read into that

//              buffer by reading from bits 25..16 of this control/status

//              register.

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

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

//

// Copyright (C) 2015-2019, 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 DMA_IDLE        3'b000

`define DMA_WAIT        3'b001

`define DMA_READ_REQ    3'b010

`define DMA_READ_ACK    3'b011

`define DMA_PRE_WRITE   3'b100

`define DMA_WRITE_REQ   3'b101

`define DMA_WRITE_ACK   3'b110

module wbdmac(i_clk, i_reset,

                i_swb_cyc, i_swb_stb, i_swb_we, i_swb_addr, i_swb_data,

                        o_swb_ack, o_swb_stall, o_swb_data,

                o_mwb_cyc, o_mwb_stb, o_mwb_we, o_mwb_addr, o_mwb_data,

                        i_mwb_ack, i_mwb_stall, i_mwb_data, i_mwb_err,

                i_dev_ints,

                o_interrupt);

        parameter       ADDRESS_WIDTH=30, LGMEMLEN = 10, DW=32;

        localparam      LGDV=5;

        localparam      AW=ADDRESS_WIDTH;

        input   wire            i_clk, i_reset;

        // Slave/control wishbone inputs

        input   wire            i_swb_cyc, i_swb_stb, i_swb_we;

        input   wire    [1:0]    i_swb_addr;

        input   wire [(DW-1):0]  i_swb_data;

        // Slave/control wishbone outputs

        output  reg             o_swb_ack;

        output  wire            o_swb_stall;

        output  reg [(DW-1):0]   o_swb_data;

        // Master/DMA wishbone control

        output  wire            o_mwb_cyc, o_mwb_stb, o_mwb_we;

        output  reg [(AW-1):0]   o_mwb_addr;

        output  reg [(DW-1):0]   o_mwb_data;

        // Master/DMA wishbone responses from the bus

        input   wire            i_mwb_ack, i_mwb_stall;

        input   wire [(DW-1):0]  i_mwb_data;

        input   wire            i_mwb_err;

        // The interrupt device interrupt lines

        input   wire [(DW-1):0]  i_dev_ints;

        // An interrupt to be set upon completion

        output  reg             o_interrupt;

        // Need to release the bus for a higher priority user

        //      This logic had lots of problems, so it is being

        //      removed.  If you want to make sure the bus is available

        //      for a higher priority user, adjust the transfer length

        //      accordingly.

        //

        // input                        i_other_busmaster_requests_bus;

        //

        wire    s_cyc, s_stb, s_we;

        wire    [1:0]    s_addr;

        wire    [31:0]   s_data;

`define DELAY_ACCESS

`ifdef  DELAY_ACCESS

        reg     r_s_cyc, r_s_stb, r_s_we;

        reg     [1:0]    r_s_addr;

        reg     [31:0]   r_s_data;

        always @(posedge i_clk)

                r_s_cyc <= i_swb_cyc;

        always @(posedge i_clk)

        if (i_reset)

                r_s_stb <= 1'b0;

        else

                r_s_stb <= i_swb_stb;

        always @(posedge i_clk)

                r_s_we  <= i_swb_we;

        always @(posedge i_clk)

                r_s_addr<= i_swb_addr;

        always @(posedge i_clk)

                r_s_data<= i_swb_data;

        assign  s_cyc = r_s_cyc;

        assign  s_stb = r_s_stb;

        assign  s_we  = r_s_we;

        assign  s_addr= r_s_addr;

        assign  s_data= r_s_data;

`else

        assign  s_cyc = i_swb_cyc;

        assign  s_stb = i_swb_stb;

        assign  s_we  = i_swb_we;

        assign  s_addr= i_swb_addr;

        assign  s_data= i_swb_data;

`endif

        reg     [2:0]            dma_state;

        reg                     cfg_err, cfg_len_nonzero;

        reg     [(AW-1):0]       cfg_waddr, cfg_raddr, cfg_len;

        reg [(LGMEMLEN-1):0]     cfg_blocklen_sub_one;

        reg                     cfg_incs, cfg_incd;

        reg     [(LGDV-1):0]     cfg_dev_trigger;

        reg                     cfg_on_dev_trigger;

        // Single block operations: We'll read, then write, up to a single

        // memory block here.

        reg     [(DW-1):0]       dma_mem [0:(((1<<LGMEMLEN))-1)];

        reg     [(LGMEMLEN):0]   nread, nwritten, nwacks, nracks;

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

        assign  bus_nracks = { {(AW-LGMEMLEN-1){1'b0}}, nracks };

        reg     last_read_request, last_read_ack,

                last_write_request, last_write_ack;

        reg     trigger, abort, user_halt;

        initial dma_state = `DMA_IDLE;

        initial o_interrupt = 1'b0;

        initial cfg_blocklen_sub_one = {(LGMEMLEN){1'b1}};

        initial cfg_on_dev_trigger = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

        begin

                dma_state <= `DMA_IDLE;

                cfg_on_dev_trigger <= 1'b0;

                cfg_incs  <= 1'b0;

                cfg_incd  <= 1'b0;

        end else case(dma_state)

        `DMA_IDLE: begin

                o_mwb_addr <= cfg_raddr;

                // When the slave wishbone writes, and we are in this 

                // (ready) configuration, then allow the DMA to be controlled

                // and thus to start.

                if ((s_stb)&&(s_we))

                begin

                        case(s_addr)

                        2'b00: begin

                                if ((s_data[27:16] == 12'hfed)

                                        &&(s_data[31:30] == 2'b00)

                                                &&(cfg_len_nonzero))

                                        dma_state <= `DMA_WAIT;

                                cfg_blocklen_sub_one

                                        <= s_data[(LGMEMLEN-1):0]

                                        + {(LGMEMLEN){1'b1}};

                                        // i.e. -1;

                                cfg_dev_trigger    <= s_data[14:10];

                                cfg_on_dev_trigger <= s_data[15];

                                cfg_incs  <= !s_data[29];

                                cfg_incd  <= !s_data[28];

                                end

                        2'b01: begin end // This is done elsewhere

                        2'b10: cfg_raddr <=  s_data[(AW+2-1):2];

                        2'b11: cfg_waddr <=  s_data[(AW+2-1):2];

                        endcase

                end end

        `DMA_WAIT: begin

                o_mwb_addr <= cfg_raddr;

                if (abort)

                        dma_state <= `DMA_IDLE;

                else if (user_halt)

                        dma_state <= `DMA_IDLE;

                else if (trigger)

                        dma_state <= `DMA_READ_REQ;

                end

        `DMA_READ_REQ: begin

                if (!i_mwb_stall)

                begin

                        // Number of read acknowledgements needed

                        if ((last_read_request)||(user_halt))

        //((nracks == {1'b0, cfg_blocklen_sub_one})||(bus_nracks == cfg_len-1))

                                // Wishbone interruptus

                                dma_state <= `DMA_READ_ACK;

                        if (cfg_incs)

                                o_mwb_addr <= o_mwb_addr

                                                + {{(AW-1){1'b0}},1'b1};

                end

                if ((i_mwb_err)||(abort))

                        dma_state <= `DMA_IDLE;

                else if (i_mwb_ack)

                begin

                        if (cfg_incs)

                                cfg_raddr  <= cfg_raddr

                                                + {{(AW-1){1'b0}},1'b1};

                        if (last_read_ack)

                                dma_state <= `DMA_PRE_WRITE;

                end end

        `DMA_READ_ACK: begin

                if ((i_mwb_err)||(abort))

                        dma_state <= `DMA_IDLE;

                else if (i_mwb_ack)

                begin

                        if (last_read_ack) // (nread+1 == nracks)

                                dma_state  <= `DMA_PRE_WRITE;

                        if (user_halt)

                                dma_state <= `DMA_IDLE;

                        if (cfg_incs)

                                cfg_raddr  <= cfg_raddr

                                                + {{(AW-1){1'b0}},1'b1};

                end

                end

        `DMA_PRE_WRITE: begin

                o_mwb_addr <= cfg_waddr;

                dma_state <= (abort)?`DMA_IDLE:`DMA_WRITE_REQ;

                end

        `DMA_WRITE_REQ: begin

                if (!i_mwb_stall)

                begin

                        if (last_write_request) // (nwritten == nread-1)

                                // Wishbone interruptus

                                dma_state <= `DMA_WRITE_ACK;

                        if (cfg_incd)

                        begin

                                o_mwb_addr <= o_mwb_addr

                                                + {{(AW-1){1'b0}},1'b1};

                                cfg_waddr  <= cfg_waddr

                                                + {{(AW-1){1'b0}},1'b1};

                        end

                end

                if ((i_mwb_err)||(abort))

                        dma_state <= `DMA_IDLE;

                else if ((i_mwb_ack)&&(last_write_ack))

                        dma_state <= (cfg_len <= 1)?`DMA_IDLE:`DMA_WAIT;

                else if (!cfg_len_nonzero)

                        dma_state <= `DMA_IDLE;

                end

        `DMA_WRITE_ACK: begin

                if ((i_mwb_err)||(abort))

                        dma_state <= `DMA_IDLE;

                else if ((i_mwb_ack)&&(last_write_ack))

                        // (nwacks+1 == nwritten)

                        dma_state <= (cfg_len <= 1)?`DMA_IDLE:`DMA_WAIT;

                else if (!cfg_len_nonzero)

                        dma_state <= `DMA_IDLE;

                end

        default:

                dma_state <= `DMA_IDLE;

        endcase

        initial o_interrupt = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                o_interrupt <= 1'b0;

        else

                o_interrupt <= ((dma_state == `DMA_WRITE_ACK)&&(i_mwb_ack)

                                        &&(last_write_ack)

                                        &&(cfg_len == {{(AW-1){1'b0}},1'b1}))

                                ||((dma_state != `DMA_IDLE)&&(i_mwb_err));

        initial cfg_len     = 0;

        initial cfg_len_nonzero = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

        begin

                cfg_len <= 0;

                cfg_len_nonzero <= 1'b0;

        end else if ((dma_state == `DMA_IDLE)

                        &&(s_stb)&&(s_we)&&(s_addr == 2'b01))

        begin

                cfg_len   <=  s_data[(AW-1):0];

                cfg_len_nonzero <= (|s_data[(AW-1):0]);

        end else if ((o_mwb_cyc)&&(o_mwb_we)&&(i_mwb_ack))

        begin

                cfg_len <= cfg_len - 1'b1;

                cfg_len_nonzero <= (cfg_len > 1);

        end

        initial nracks   = 0;

        always @(posedge i_clk)

        if (i_reset)

                nracks <= 0;

        else if ((dma_state == `DMA_IDLE)||(dma_state == `DMA_WAIT))

                nracks <= 0;

        else if ((o_mwb_stb)&&(!o_mwb_we)&&(!i_mwb_stall))

                nracks <= nracks + 1'b1;

        initial nread   = 0;

        always @(posedge i_clk)

        if (i_reset)

                nread <= 0;

        else if ((dma_state == `DMA_IDLE)||(dma_state == `DMA_WAIT))

                nread <= 0;

        else if ((!o_mwb_we)&&(i_mwb_ack))

                nread <= nread + 1'b1;

        initial nwritten = 0;

        always @(posedge i_clk)

        if (i_reset)

                nwritten <= 0;

        else if ((!o_mwb_cyc)||(!o_mwb_we))

                nwritten <= 0;

        else if ((o_mwb_stb)&&(!i_mwb_stall))

                nwritten <= nwritten + 1'b1;

        initial nwacks   = 0;

        always @(posedge i_clk)

        if (i_reset)

                nwacks <= 0;

        else if ((!o_mwb_cyc)||(!o_mwb_we))

                nwacks <= 0;

        else if (i_mwb_ack)

                nwacks <= nwacks + 1'b1;

        initial cfg_err = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                cfg_err <= 1'b0;

        else if (dma_state == `DMA_IDLE)

        begin

                if ((s_stb)&&(s_we)&&(s_addr==2'b00))

                        cfg_err <= 1'b0;

        end else if (((i_mwb_err)&&(o_mwb_cyc))||(abort))

                cfg_err <= 1'b1;

        initial last_read_request = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                last_read_request <= 1'b0;

        else if ((dma_state == `DMA_WAIT)||(dma_state == `DMA_READ_REQ))

        begin

                if ((!i_mwb_stall)&&(dma_state == `DMA_READ_REQ))

                begin

                        last_read_request <=

                        (nracks + 1 == { 1'b0, cfg_blocklen_sub_one})

                                ||(bus_nracks == cfg_len-2);

                end else

                        last_read_request <=

                                (nracks== { 1'b0, cfg_blocklen_sub_one})

                                ||(bus_nracks == cfg_len-1);

        end else

                last_read_request <= 1'b0;

        wire    [(LGMEMLEN):0]   next_nread;

        assign  next_nread = nread + 1'b1;

        initial last_read_ack = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                last_read_ack <= 0;

        else if (dma_state == `DMA_READ_REQ)

        begin

                if ((i_mwb_ack)&&((!o_mwb_stb)||(i_mwb_stall)))

                        last_read_ack <= (next_nread == { 1'b0, cfg_blocklen_sub_one });

                else

                        last_read_ack <= (nread == { 1'b0, cfg_blocklen_sub_one });

        end else if (dma_state == `DMA_READ_ACK)

        begin

                if ((i_mwb_ack)&&((!o_mwb_stb)||(i_mwb_stall)))

                        last_read_ack <= (nread+2 == nracks);

                else

                        last_read_ack <= (next_nread == nracks);

        end else

                last_read_ack <= 1'b0;

        initial last_write_request = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                last_write_request <= 1'b0;

        else if (dma_state == `DMA_PRE_WRITE)

                last_write_request <= (nread <= 1);

        else if (dma_state == `DMA_WRITE_REQ)

        begin

                if (i_mwb_stall)

                        last_write_request <= (nwritten >= nread-1);

                else

                        last_write_request <= (nwritten >= nread-2);

        end else

                last_write_request <= 1'b0;

        initial last_write_ack = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                last_write_ack <= 1'b0;

        else if((dma_state == `DMA_WRITE_REQ)||(dma_state == `DMA_WRITE_ACK))

        begin

                if ((i_mwb_ack)&&((!o_mwb_stb)||(i_mwb_stall)))

                        last_write_ack <= (nwacks+2 == nwritten);

                else

                        last_write_ack <= (nwacks+1 == nwritten);

        end else

                last_write_ack <= 1'b0;

        assign  o_mwb_cyc = (dma_state == `DMA_READ_REQ)

                        ||(dma_state == `DMA_READ_ACK)

                        ||(dma_state == `DMA_WRITE_REQ)

                        ||(dma_state == `DMA_WRITE_ACK);

        assign  o_mwb_stb = (dma_state == `DMA_READ_REQ)

                        ||(dma_state == `DMA_WRITE_REQ);

        assign  o_mwb_we = (dma_state == `DMA_PRE_WRITE)

                        ||(dma_state == `DMA_WRITE_REQ)

                        ||(dma_state == `DMA_WRITE_ACK);

        //

        // This is tricky.  In order for Vivado to consider dma_mem to be a 

        // proper memory, it must have a simple address fed into it.  Hence

        // the read_address (rdaddr) register.  The problem is that this

        // register must always be one greater than the address we actually

        // want to read from, unless we are idling.  So ... the math is touchy.

        //

        reg     [(LGMEMLEN-1):0] rdaddr;

        initial rdaddr = 0;

        always @(posedge i_clk)

        if (i_reset)

                rdaddr <= 0;

        else if((dma_state == `DMA_IDLE)||(dma_state == `DMA_WAIT)

                        ||(dma_state == `DMA_WRITE_ACK))

                rdaddr <= 0;

        else if ((dma_state == `DMA_PRE_WRITE)

                        ||((dma_state==`DMA_WRITE_REQ)&&(!i_mwb_stall)))

                rdaddr <= rdaddr + {{(LGMEMLEN-1){1'b0}},1'b1};

        always @(posedge i_clk)

        if (i_reset)

                o_mwb_data <= 0;

        else if ((dma_state != `DMA_WRITE_REQ)||(!i_mwb_stall))

                o_mwb_data <= dma_mem[rdaddr];

        always @(posedge i_clk)

                if((dma_state == `DMA_READ_REQ)||(dma_state == `DMA_READ_ACK))

                        dma_mem[nread[(LGMEMLEN-1):0]] <= i_mwb_data;

        always @(posedge i_clk)

        if (i_reset)

                o_swb_data <= 0;

        else casez(s_addr)

                2'b00: o_swb_data <= {  (dma_state != `DMA_IDLE), cfg_err,

                                        !cfg_incs, !cfg_incd,

                                        1'b0, nread,

                                        cfg_on_dev_trigger, cfg_dev_trigger,

                                        cfg_blocklen_sub_one

                                        };

                2'b01: o_swb_data <= { {(DW-AW){1'b0}}, cfg_len  };

                2'b10: o_swb_data <= { {(DW-2-AW){1'b0}}, cfg_raddr, 2'b00 };

                2'b11: o_swb_data <= { {(DW-2-AW){1'b0}}, cfg_waddr, 2'b00 };

        endcase

        // This causes us to wait a minimum of two clocks before starting: One

        // to go into the wait state, and then one while in the wait state to

        // develop the trigger.

        initial trigger = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                trigger <= 1'b0;

        else

                trigger <=  (dma_state == `DMA_WAIT)

                                &&((!cfg_on_dev_trigger)

                                        ||(i_dev_ints[cfg_dev_trigger]));

        // Ack any access.  We'll quietly ignore any access where we are busy,

        // but ack it anyway.  In other words, before writing to the device,

        // double check that it isn't busy, and then write.

        initial o_swb_ack = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                o_swb_ack <= 1'b0;

        else if (!i_swb_cyc)

                o_swb_ack <= 1'b0;

        else

                o_swb_ack <= (s_stb);

        assign  o_swb_stall = 1'b0;

        initial abort = 1'b0;

        always @(posedge i_clk)

        if (i_reset)

                abort <= 1'b0;

        else if (dma_state == `DMA_IDLE)

                abort <= 1'b0;

        else

                abort <= ((s_stb)&&(s_we)

                        &&(s_addr == 2'b00)

                        &&(s_data == 32'hffed0000));

        initial user_halt = 1'b0;

        always @(posedge i_clk)

                user_halt <= ((user_halt)&&(dma_state != `DMA_IDLE))

                        ||((s_stb)&&(s_we)&&(dma_state != `DMA_IDLE)

                                &&(s_addr == 2'b00)

                                &&(s_data == 32'hafed0000));

        // Make verilator happy

        // verilator lint_off UNUSED

        wire    unused;

        assign  unused = s_cyc;

        // verilator lint_on  UNUSED

`ifdef  FORMAL

        reg     f_past_valid;

        initial f_past_valid = 1'b0;

        always @(posedge i_clk)

                f_past_valid <= 1'b1;

        always @(*)

        if (!f_past_valid)

                assume(i_reset);

        always @(posedge i_clk)