SummerCart64/fw/rtl/memory/memory_dma.sv

module memory_dma (
    input clk,
    input reset,

    dma_scb.dma dma_scb,

    fifo_bus.controller fifo_bus,
    mem_bus.controller mem_bus
);

    // Start/stop logic

    logic dma_start;
    logic dma_stop;

    always_ff @(posedge clk) begin
        dma_start <= 1'b0;
        if (dma_scb.stop) begin
            dma_stop <= 1'b1;
        end else if (dma_scb.start) begin
            dma_start <= 1'b1;
            dma_stop <= 1'b0;
        end
    end


    // Memory bus controller

    typedef enum bit [1:0] {
        MEM_BUS_STATE_IDLE,
        MEM_BUS_STATE_WAIT,
        MEM_BUS_STATE_TRANSFER
    } e_mem_bus_state;

    e_mem_bus_state mem_bus_state;
    e_mem_bus_state next_mem_bus_state;

    logic mem_bus_wdata_buffer_ready;
    // logic mem_bus_wdata_buffer_ack;
    // logic [1:0] mem_bus_wmask_buffer;
    logic [1:0] mem_bus_wdata_valid;
    logic [15:0] mem_bus_wdata_buffer;

    logic mem_bus_rdata_ready;
    logic mem_bus_rdata_ack;
    logic mem_bus_rdata_end;
    logic [1:0] mem_bus_rdata_valid;
    logic [15:0] mem_bus_rdata_buffer;

    logic [26:0] mem_bus_remaining_bytes;
    logic mem_bus_last_transfer;
    logic mem_bus_almost_last_transfer;
    logic mem_bus_unaligned_start;
    logic mem_bus_unaligned_end;

    always_ff @(posedge clk) begin
        if (reset) begin
            mem_bus_state <= MEM_BUS_STATE_IDLE;
        end else begin
            mem_bus_state <= next_mem_bus_state;
        end
    end

    always_comb begin
        next_mem_bus_state = mem_bus_state;

        mem_bus_last_transfer = (mem_bus_remaining_bytes == 27'd0);
        mem_bus_almost_last_transfer = (mem_bus_remaining_bytes <= 27'd2);

        case (mem_bus_state)
            MEM_BUS_STATE_IDLE: begin
                if (dma_start) begin
                    next_mem_bus_state = MEM_BUS_STATE_WAIT;
                end
            end

            MEM_BUS_STATE_WAIT: begin
                if (dma_stop || mem_bus_last_transfer) begin
                    next_mem_bus_state = MEM_BUS_STATE_IDLE;
                end else if (mem_bus_wdata_buffer_ready || mem_bus_rdata_ready) begin
                    next_mem_bus_state = MEM_BUS_STATE_TRANSFER;
                end
            end

            MEM_BUS_STATE_TRANSFER: begin
                if (mem_bus.ack) begin
                    if (dma_stop || mem_bus_last_transfer) begin
                        next_mem_bus_state = MEM_BUS_STATE_IDLE;
                    end else if (!(mem_bus_wdata_buffer_ready || mem_bus_rdata_ready)) begin
                        next_mem_bus_state = MEM_BUS_STATE_WAIT;
                    end
                end
            end

            default: begin
                next_mem_bus_state = MEM_BUS_STATE_IDLE;
            end
        endcase
    end

    always_ff @(posedge clk) begin
        mem_bus_rdata_ack <= 1'b0;

        if (mem_bus.ack) begin
            mem_bus.request <= 1'b0;
            mem_bus.address <= (mem_bus.address + 26'd2);
            mem_bus_rdata_ack <= 1'b1;
            mem_bus_rdata_end <= mem_bus_last_transfer;
            mem_bus_rdata_valid <= mem_bus.wmask;
            mem_bus_rdata_buffer <= mem_bus.rdata;
        end

        case (mem_bus_state)
            MEM_BUS_STATE_IDLE: begin
                mem_bus.request <= 1'b0;
                mem_bus_rdata_end <= 1'b1;
                if (dma_start) begin
                    mem_bus.write <= dma_scb.direction;
                    mem_bus.address <= {dma_scb.starting_address[26:1], 1'b0};
                    mem_bus_remaining_bytes <= dma_scb.transfer_length;
                    mem_bus_unaligned_start <= dma_scb.starting_address[0];
                    mem_bus_unaligned_end <= (dma_scb.starting_address[0] ^ dma_scb.transfer_length[0]);
                    mem_bus_rdata_end <= 1'b0;
                end
            end

            MEM_BUS_STATE_WAIT: begin
                if (!dma_stop && !mem_bus_last_transfer) begin
                    if (mem_bus_wdata_buffer_ready || mem_bus_rdata_ready) begin
                        mem_bus.request <= 1'b1;
                        mem_bus_unaligned_start <= 1'b0;
                        mem_bus.wdata <= (dma_scb.byte_swap ? {mem_bus_wdata_buffer[7:0], mem_bus_wdata_buffer[15:8]} : mem_bus_wdata_buffer);
                        mem_bus.wmask <= 2'b11;
                        mem_bus_remaining_bytes <= (mem_bus_remaining_bytes - 27'd2);
                        if (mem_bus_unaligned_end && mem_bus_almost_last_transfer) begin
                            mem_bus.wmask <= 2'b10;
                            mem_bus_remaining_bytes <= (mem_bus_remaining_bytes - 27'd1);
                        end
                        if (mem_bus_unaligned_start) begin
                            mem_bus.wmask <= 2'b01;
                            mem_bus_remaining_bytes <= (mem_bus_remaining_bytes - 27'd1);
                        end
                    end
                end
            end

            MEM_BUS_STATE_TRANSFER: begin
                if (!dma_stop && !mem_bus_last_transfer) begin
                    if (mem_bus.ack && (mem_bus_wdata_buffer_ready || mem_bus_rdata_ready)) begin
                        mem_bus.request <= 1'b1;
                        mem_bus.wdata <= (dma_scb.byte_swap ? {mem_bus_wdata_buffer[7:0], mem_bus_wdata_buffer[15:8]} : mem_bus_wdata_buffer);
                        mem_bus.wmask <= 2'b11;
                        mem_bus_remaining_bytes <= (mem_bus_remaining_bytes - 27'd2);
                        if (mem_bus_unaligned_end && mem_bus_almost_last_transfer) begin
                            mem_bus.wmask <= 2'b10;
                            mem_bus_remaining_bytes <= (mem_bus_remaining_bytes - 27'd1);
                        end
                    end
                end
            end

            default: begin end
        endcase
    end

    assign mem_bus_wdata_buffer_ready = 1'b0;
    // assign mem_bus_rdata_ready = 1'b1;


    // RX FIFO controller

    // typedef enum bit [1:0] {
    //     RX_FIFO_BUS_STATE_IDLE,
    //     RX_FIFO_BUS_STATE_TRANSFER_1,
    //     RX_FIFO_BUS_STATE_TRANSFER_2,
    //     RX_FIFO_BUS_STATE_WAIT
    // } e_rx_fifo_bus_state;

    // e_rx_fifo_bus_state rx_fifo_bus_state;
    // e_rx_fifo_bus_state next_rx_fifo_bus_state;

    // logic rx_fifo_read_delayed;
    // logic rx_fifo_buffer_shift;
    // logic rx_fifo_unaligned_start;
    // logic rx_fifo_unaligned_end;

    always_ff @(posedge clk) begin
        // if (reset || dma_stop) begin
        //     rx_fifo_bus_state <= RX_FIFO_BUS_STATE_IDLE;
        // end else begin
        //     rx_fifo_bus_state <= next_rx_fifo_bus_state;
        // end
    end

    always_comb begin
        // next_rx_fifo_bus_state = rx_fifo_bus_state;

        // fifo_bus.rx_read = 1'b0;
        // rx_fifo_buffer_shift = 1'b0;

        // case (rx_fifo_bus_state)
        //     RX_FIFO_BUS_STATE_IDLE: begin
        //         if (dma_start && dma_scb.direction) begin
        //             next_rx_fifo_bus_state = RX_FIFO_BUS_STATE_TRANSFER_1;
        //             if (dma_scb.starting_address[0]) begin
        //                 next_rx_fifo_bus_state = RX_FIFO_BUS_STATE_TRANSFER_2;
        //             end
        //         end
        //     end

        //     RX_FIFO_BUS_STATE_TRANSFER_1,
        //     RX_FIFO_BUS_STATE_TRANSFER_2: begin
        //         fifo_bus.rx_read = (!no_bytes_left && !fifo_bus.rx_empty);
        //         rx_fifo_buffer_shift = no_bytes_left;
        //         if (fifo_bus.rx_read || no_bytes_left) begin
        //             if (rx_fifo_bus_state == RX_FIFO_BUS_STATE_TRANSFER_1) begin
        //                 next_rx_fifo_bus_state = RX_FIFO_BUS_STATE_TRANSFER_2;
        //             end else begin
        //                 next_rx_fifo_bus_state = RX_FIFO_BUS_STATE_WAIT;
        //             end
        //         end
        //     end

        //     RX_FIFO_BUS_STATE_WAIT: begin
        //         if (mem_bus_wdata_buffer_ready && mem_bus_wdata_buffer_ack) begin
        //             if (no_bytes_left) begin
        //                 next_rx_fifo_bus_state = RX_FIFO_BUS_STATE_IDLE;
        //             end else begin
        //                 next_rx_fifo_bus_state = RX_FIFO_BUS_STATE_TRANSFER_1;
        //             end
        //         end
        //     end

        //     default: begin
        //         next_rx_fifo_bus_state = RX_FIFO_BUS_STATE_IDLE;
        //     end
        // endcase
    end

    always_ff @(posedge clk) begin
        // rx_fifo_read_delayed <= (fifo_bus.rx_read || rx_fifo_buffer_shift);

        // if (rx_fifo_read_delayed) begin
        //     mem_bus_wdata_buffer <= {mem_bus_wdata_buffer[7:0], fifo_bus.rx_rdata};
        // end

        // case (rx_fifo_bus_state)
        //     RX_FIFO_BUS_STATE_IDLE: begin
        //         mem_bus_wdata_buffer_ready <= 1'b0;
        //         if (dma_start) begin
        //             mem_bus_rx_transfer_end <= 1'b0;
        //             rx_fifo_unaligned_start <= dma_scb.starting_address[0];
        //             rx_fifo_unaligned_end <= (dma_scb.starting_address[0] ^ dma_scb.transfer_length[0]);
        //         end
        //     end

        //     RX_FIFO_BUS_STATE_TRANSFER_1,
        //     RX_FIFO_BUS_STATE_TRANSFER_2: begin end

        //     RX_FIFO_BUS_STATE_WAIT: begin
        //         mem_bus_wdata_buffer_ready <= 1'b1;
        //         mem_bus_wmask_buffer <= 2'b11;
        //         if (rx_fifo_unaligned_start) begin
        //             mem_bus_wmask_buffer <= 2'b01;
        //         end
        //         if (no_bytes_left) begin
        //             mem_bus_rx_transfer_end <= 1'b1;
        //             if (rx_fifo_unaligned_end) begin
        //                 mem_bus_wmask_buffer <= 2'b10;
        //             end
        //         end
        //         if (mem_bus_wdata_buffer_ack) begin
        //             rx_fifo_unaligned_start <= 1'b0;
        //             mem_bus_wdata_buffer_ready <= 1'b0;
        //         end
        //     end

        //     default: begin end
        // endcase
    end


    // TX FIFO controller

    typedef enum bit [1:0] {
        TX_FIFO_BUS_STATE_IDLE,
        TX_FIFO_BUS_STATE_WAIT,
        TX_FIFO_BUS_STATE_TRANSFER_1,
        TX_FIFO_BUS_STATE_TRANSFER_2
    } e_tx_fifo_bus_state;

    e_tx_fifo_bus_state tx_fifo_bus_state;
    e_tx_fifo_bus_state next_tx_fifo_bus_state;

    logic tx_fifo_shift;
    logic tx_fifo_waiting;
    logic [1:0] tx_fifo_valid;
    logic [15:0] tx_fifo_buffer;

    always_ff @(posedge clk) begin
        if (reset || dma_stop) begin
            tx_fifo_bus_state <= TX_FIFO_BUS_STATE_IDLE;
        end else begin
            tx_fifo_bus_state <= next_tx_fifo_bus_state;
        end
    end

    always_comb begin
        next_tx_fifo_bus_state = tx_fifo_bus_state;

        tx_fifo_shift = 1'b0;

        fifo_bus.tx_write = 1'b0;
        fifo_bus.tx_wdata = tx_fifo_buffer[15:8];

        case (tx_fifo_bus_state)
            TX_FIFO_BUS_STATE_IDLE: begin
                if (dma_start && !dma_scb.direction) begin
                    next_tx_fifo_bus_state = TX_FIFO_BUS_STATE_WAIT;
                end
            end

            TX_FIFO_BUS_STATE_WAIT: begin
                if (mem_bus_rdata_ack || tx_fifo_waiting) begin
                    next_tx_fifo_bus_state = TX_FIFO_BUS_STATE_TRANSFER_1;
                end else if (mem_bus_rdata_end) begin
                    next_tx_fifo_bus_state = TX_FIFO_BUS_STATE_IDLE;
                end
            end

            TX_FIFO_BUS_STATE_TRANSFER_1: begin
                fifo_bus.tx_write = (!fifo_bus.tx_full && tx_fifo_valid[1]);
                if (fifo_bus.tx_write || !tx_fifo_valid[1]) begin
                    next_tx_fifo_bus_state = TX_FIFO_BUS_STATE_TRANSFER_2;
                    tx_fifo_shift = 1'b1;
                end
            end

            TX_FIFO_BUS_STATE_TRANSFER_2: begin
                fifo_bus.tx_write = (!fifo_bus.tx_full && tx_fifo_valid[1]);
                if (fifo_bus.tx_write || !tx_fifo_valid[1]) begin
                    next_tx_fifo_bus_state = TX_FIFO_BUS_STATE_WAIT;
                    tx_fifo_shift = 1'b1;
                    if (!mem_bus_rdata_ack && !tx_fifo_waiting && mem_bus_rdata_end) begin
                        next_tx_fifo_bus_state = TX_FIFO_BUS_STATE_IDLE;
                    end
                end
            end

            default: begin
                next_tx_fifo_bus_state = TX_FIFO_BUS_STATE_IDLE;
            end
        endcase
    end

    always_ff @(posedge clk) begin
        if (tx_fifo_shift) begin
            tx_fifo_valid <= {tx_fifo_valid[0], 1'bX};
            tx_fifo_buffer <= {tx_fifo_buffer[7:0], 8'hXX};
        end

        case (tx_fifo_bus_state)
            TX_FIFO_BUS_STATE_IDLE: begin
                mem_bus_rdata_ready <= 1'b0;
                tx_fifo_waiting <= 1'b0;
                if (dma_start) begin
                    mem_bus_rdata_ready <= !dma_scb.direction;
                end
            end

            TX_FIFO_BUS_STATE_WAIT: begin
                if (mem_bus_rdata_ack || tx_fifo_waiting) begin
                    mem_bus_rdata_ready <= 1'b0;
                    tx_fifo_waiting <= 1'b0;
                    tx_fifo_valid <= mem_bus_rdata_valid;
                    tx_fifo_buffer <= mem_bus_rdata_buffer;
                end
            end

            TX_FIFO_BUS_STATE_TRANSFER_1: begin
                if (mem_bus_rdata_ack) begin
                    tx_fifo_waiting <= 1'b1;
                end
            end

            TX_FIFO_BUS_STATE_TRANSFER_2: begin
                if (mem_bus_rdata_ack) begin
                    tx_fifo_waiting <= 1'b1;
                end
                if (fifo_bus.tx_write || !tx_fifo_valid[1]) begin
                    mem_bus_rdata_ready <= !mem_bus_rdata_end;
                end
            end

            default: begin end
        endcase
    end


    // DMA busy indicator

    always_ff @(posedge clk) begin
        dma_scb.busy <= (
            (dma_scb.start && !dma_scb.stop) ||
            dma_start ||
            (mem_bus_state != MEM_BUS_STATE_IDLE) ||
            // (rx_fifo_bus_state != RX_FIFO_BUS_STATE_IDLE) ||
            (tx_fifo_bus_state != TX_FIFO_BUS_STATE_IDLE)
        );
    end

endmodule