redpitaya-puzzlefw/fpga/rtl/puzzlefw_top.vhd

--
--  Top-level FPGA design for Red Pitaya PuzzleFW firmware.
--
--  Joris van Rantwijk 2024
--

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_misc.all;
use ieee.numeric_std.all;

library unisim;
use unisim.vcomponents.all;

library xpm;
use xpm.vcomponents.all;

use work.puzzlefw_pkg.all;


entity puzzlefw_top is

    port (

        -- Ports directly connected to ARM/PS.
        DDR_0_addr:         inout std_logic_vector(14 downto 0);
        DDR_0_ba:           inout std_logic_vector(2 downto 0);
        DDR_0_cas_n:        inout std_logic;
        DDR_0_ck_n:         inout std_logic;
        DDR_0_ck_p:         inout std_logic;
        DDR_0_cke:          inout std_logic;
        DDR_0_cs_n:         inout std_logic;
        DDR_0_dm:           inout std_logic_vector(3 downto 0);
        DDR_0_dq:           inout std_logic_vector(31 downto 0);
        DDR_0_dqs_n:        inout std_logic_vector(3 downto 0);
        DDR_0_dqs_p:        inout std_logic_vector(3 downto 0);
        DDR_0_odt:          inout std_logic;
        DDR_0_ras_n:        inout std_logic;
        DDR_0_reset_n:      inout std_logic;
        DDR_0_we_n:         inout std_logic;
        FIXED_IO_0_ddr_vrn: inout std_logic;
        FIXED_IO_0_ddr_vrp: inout std_logic;
        FIXED_IO_0_mio:     inout std_logic_vector(53 downto 0);
        FIXED_IO_0_ps_clk:  inout std_logic;
        FIXED_IO_0_ps_porb: inout std_logic;
        FIXED_IO_0_ps_srstb: inout std_logic;

        -- Ports controlled by FPGA.
        adc_dat_i:          in  adc_data_input_type;                -- ADC data
        adc_clk_i:          in  std_logic_vector(1 downto 0);       -- ADC clock 1=pos, 0=neg
        adc_clk_o:          out std_logic_vector(1 downto 0);       -- optional clock output for ADC
        adc_cdcs_o:         out std_logic;                          -- ADC clock duty cycle stabilizer
        dac_dat_o:          out std_logic_vector(13 downto 0);      -- DAC data
        dac_wrt_o:          out std_logic;                          -- DAC write control
        dac_sel_o:          out std_logic;                          -- DAC channel select
        dac_clk_o:          out std_logic;                          -- DAC clock
        dac_rst_o:          out std_logic;                          -- DAC reset
        dac_pwm_o:          out std_logic_vector(3 downto 0);       -- PWM DAC
        exp_p_io:           inout std_logic_vector(7 downto 0);     -- extension I/O pos
        exp_n_io:           inout std_logic_vector(7 downto 0);     -- extension I/O neg
        led_o:              out std_logic_vector(7 downto 0)        -- LEDs
    );

end puzzlefw_top;

architecture arch of puzzlefw_top is

    -- Main 125 MHz clock, derived from ADC clock input port.
    signal clk_adc:         std_logic;

    -- Auxiliary clock from FCLK0.
    signal clk_fclk:        std_logic;

    -- Main reset signal, derived from FCLK_RESET0, active high, synchronous to clk_adc.
    signal s_reset:         std_logic;

    -- Internal clock signal.
    signal s_adc_clk_ibuf:  std_logic;

    -- Blinking LED.
    signal r_adcclk_cnt:    unsigned(25 downto 0);
    signal r_adcclk_led:    std_logic;

    -- APB bus for register access.
    signal s_apb_paddr:     std_logic_vector(31 downto 0);
    signal s_apb_penable:   std_logic;
    signal s_apb_prdata:    std_logic_vector(31 downto 0);
    signal s_apb_pready:    std_logic;
    signal s_apb_psel:      std_logic;
    signal s_apb_pslverr:   std_logic;
    signal s_apb_pwdata:    std_logic_vector(31 downto 0);
    signal s_apb_pwrite:    std_logic;

    -- AXI bus for DMA.
    signal s_axi_awid:      std_logic_vector(5 downto 0);
    signal s_axi_awaddr:    std_logic_vector(31 downto 0);
    signal s_axi_awlen:     std_logic_vector(3 downto 0);
    signal s_axi_awsize:    std_logic_vector(2 downto 0);
    signal s_axi_awburst:   std_logic_vector(1 downto 0);
    signal s_axi_awlock:    std_logic_vector(1 downto 0);
    signal s_axi_awcache:   std_logic_vector(3 downto 0);
    signal s_axi_awprot:    std_logic_vector(2 downto 0);
    signal s_axi_awqos:     std_logic_vector(3 downto 0);
    signal s_axi_awvalid:   std_logic;
    signal s_axi_awready:   std_logic;
    signal s_axi_wid:       std_logic_vector(5 downto 0);
    signal s_axi_wdata:     std_logic_vector(63 downto 0);
    signal s_axi_wstrb:     std_logic_vector(7 downto 0);
    signal s_axi_wlast:     std_logic;
    signal s_axi_wvalid:    std_logic;
    signal s_axi_wready:    std_logic;
    signal s_axi_bid:       std_logic_vector(5 downto 0);
    signal s_axi_bresp:     std_logic_vector(1 downto 0);
    signal s_axi_bvalid:    std_logic;
    signal s_axi_bready:    std_logic;
    signal s_axi_arid:      std_logic_vector(5 downto 0);
    signal s_axi_araddr:    std_logic_vector(31 downto 0);
    signal s_axi_arlen:     std_logic_vector(3 downto 0);
    signal s_axi_arsize:    std_logic_vector(2 downto 0);
    signal s_axi_arburst:   std_logic_vector(1 downto 0);
    signal s_axi_arlock:    std_logic_vector(1 downto 0);
    signal s_axi_arcache:   std_logic_vector(3 downto 0);
    signal s_axi_arprot:    std_logic_vector(2 downto 0);
    signal s_axi_arqos:     std_logic_vector(3 downto 0);
    signal s_axi_arvalid:   std_logic;
    signal s_axi_arready:   std_logic;
    signal s_axi_rid:       std_logic_vector(5 downto 0);
    signal s_axi_rdata:     std_logic_vector(63 downto 0);
    signal s_axi_rresp:     std_logic_vector(1 downto 0);
    signal s_axi_rlast:     std_logic;
    signal s_axi_rvalid:    std_logic;
    signal s_axi_rready:    std_logic;

    -- Interrupts.
    signal s_irq_pending:   std_logic_vector(1 downto 0);
    signal s_irq_f2p:       std_logic_vector(7 downto 0);

    -- Registers.
    signal s_reg_control:   registers_control;
    signal s_reg_status:    registers_status;

    -- DMA write channel control.
    signal s_dma_write_cmd_addr:    dma_address_array(0 to 1);
    signal s_dma_write_cmd_length:  dma_burst_length_array(0 to 1);
    signal s_dma_write_cmd_valid:   std_logic_vector(1 downto 0);
    signal s_dma_write_cmd_ready:   std_logic_vector(1 downto 0);
    signal s_dma_write_data:        dma_data_array(0 to 1);
    signal s_dma_write_data_ready:  std_logic_vector(1 downto 0);
    signal s_dma_write_finished:    std_logic_vector(1 downto 0);

    signal s_acq_dma_valid: std_logic;
    signal s_acq_dma_ready: std_logic;
    signal s_acq_dma_empty: std_logic;
    signal s_acq_dma_data:  dma_data_type;

    signal s_tt_dma_valid:  std_logic;
    signal s_tt_dma_ready:  std_logic;
    signal s_tt_dma_empty:  std_logic;
    signal s_tt_dma_data:   dma_data_type;

    signal s_timestamp:     std_logic_vector(timestamp_bits - 1 downto 0);
    signal s_adc_data:      adc_data_array(0 to 1);
    signal s_adc_sample:    adc_data_array(0 to 1);
    signal s_dig_in:        std_logic_vector(3 downto 0);
    signal s_dig_sync:      std_logic_vector(3 downto 0);
    signal s_dig_deglitch:  std_logic_vector(3 downto 0);
    signal s_dig_sample:    std_logic_vector(3 downto 0);

begin

    -- Drive LEDs.
    led_o(0)    <= r_adcclk_led;                    -- blinking LED, 1 Hz
    led_o(1)    <= s_reg_control.acquisition_en;    -- acquisition enabled
    led_o(2)    <= s_reg_status.trig_waiting;       -- waiting for trigger
    led_o(3)    <= or_reduce(s_reg_control.timetagger_en);  -- timetagger enabled
    led_o(7 downto 4) <= s_reg_control.led_state(7 downto 4);

    -- Enable ADC clock duty cycle stabilizer.
    adc_cdcs_o  <= '1';

    -- ADC clock outputs are not connected on vanilla Red Pitaya 125-14.
    adc_clk_o   <= (others => 'Z');

    -- Drive safe levels to unused DAC pins.
    dac_dat_o   <= (others => '0');
    dac_wrt_o   <= '0';
    dac_sel_o   <= '0';
    dac_clk_o   <= '0';
    dac_rst_o   <= '0';
    dac_pwm_o   <= (others => 'Z');

    -- Use extension I/O pins as inputs only.
    exp_p_io    <= (others => 'Z');
    exp_n_io    <= (others => 'Z');

    -- Differential clock input for ADC clock.
    inst_ibuf_adc_clk: IBUFDS
        port map (
            O => s_adc_clk_ibuf,
            I => adc_clk_i(1),
            IB => adc_clk_i(0)
        );

    -- Clock buffer for ADC clock.
    inst_bufg_adc_clk: BUFG
        port map (
            I => s_adc_clk_ibuf,
            O => clk_adc
        );

    -- ARM/PS block design.
    inst_blockdesign: entity work.puzzlefw_wrapper
        port map (
            sys_clk             => clk_adc,
            ps_fclk             => clk_fclk,
            peripheral_reset_0(0) => s_reset,
            DDR_0_addr          => DDR_0_addr,
            DDR_0_ba            => DDR_0_ba,
            DDR_0_cas_n         => DDR_0_cas_n,
            DDR_0_ck_n          => DDR_0_ck_n,
            DDR_0_ck_p          => DDR_0_ck_p,
            DDR_0_cke           => DDR_0_cke,
            DDR_0_cs_n          => DDR_0_cs_n,
            DDR_0_dm            => DDR_0_dm,
            DDR_0_dq            => DDR_0_dq,
            DDR_0_dqs_n         => DDR_0_dqs_n,
            DDR_0_dqs_p         => DDR_0_dqs_p,
            DDR_0_odt           => DDR_0_odt,
            DDR_0_ras_n         => DDR_0_ras_n,
            DDR_0_reset_n       => DDR_0_reset_n,
            DDR_0_we_n          => DDR_0_we_n,
            FIXED_IO_0_ddr_vrn  => FIXED_IO_0_ddr_vrn,
            FIXED_IO_0_ddr_vrp  => FIXED_IO_0_ddr_vrp,
            FIXED_IO_0_mio      => FIXED_IO_0_mio,
            FIXED_IO_0_ps_clk   => FIXED_IO_0_ps_clk,
            FIXED_IO_0_ps_porb  => FIXED_IO_0_ps_porb,
            FIXED_IO_0_ps_srstb => FIXED_IO_0_ps_srstb,
            APB_M_0_paddr       => s_apb_paddr,
            APB_M_0_penable     => s_apb_penable,
            APB_M_0_prdata      => s_apb_prdata,
            APB_M_0_pready(0)   => s_apb_pready,
            APB_M_0_psel(0)     => s_apb_psel,
            APB_M_0_pslverr(0)  => s_apb_pslverr,
            APB_M_0_pwdata      => s_apb_pwdata,
            APB_M_0_pwrite      => s_apb_pwrite,
            IRQ_F2P             => s_irq_f2p,
            S_AXI_HP0_0_araddr  => s_axi_araddr,
            S_AXI_HP0_0_arburst => s_axi_arburst,
            S_AXI_HP0_0_arcache => s_axi_arcache,
            S_AXI_HP0_0_arid    => s_axi_arid,
            S_AXI_HP0_0_arlen   => s_axi_arlen,
            S_AXI_HP0_0_arlock  => s_axi_arlock,
            S_AXI_HP0_0_arprot  => s_axi_arprot,
            S_AXI_HP0_0_arqos   => s_axi_arqos,
            S_AXI_HP0_0_arready => s_axi_arready,
            S_AXI_HP0_0_arsize  => s_axi_arsize,
            S_AXI_HP0_0_arvalid => s_axi_arvalid,
            S_AXI_HP0_0_awaddr  => s_axi_awaddr,
            S_AXI_HP0_0_awburst => s_axi_awburst,
            S_AXI_HP0_0_awcache => s_axi_awcache,
            S_AXI_HP0_0_awid    => s_axi_awid,
            S_AXI_HP0_0_awlen   => s_axi_awlen,
            S_AXI_HP0_0_awlock  => s_axi_awlock,
            S_AXI_HP0_0_awprot  => s_axi_awprot,
            S_AXI_HP0_0_awqos   => s_axi_awqos,
            S_AXI_HP0_0_awready => s_axi_awready,
            S_AXI_HP0_0_awsize  => s_axi_awsize,
            S_AXI_HP0_0_awvalid => s_axi_awvalid,
            S_AXI_HP0_0_bid     => s_axi_bid,
            S_AXI_HP0_0_bready  => s_axi_bready,
            S_AXI_HP0_0_bresp   => s_axi_bresp,
            S_AXI_HP0_0_bvalid  => s_axi_bvalid,
            S_AXI_HP0_0_rdata   => s_axi_rdata,
            S_AXI_HP0_0_rid     => s_axi_rid,
            S_AXI_HP0_0_rlast   => s_axi_rlast,
            S_AXI_HP0_0_rready  => s_axi_rready,
            S_AXI_HP0_0_rresp   => s_axi_rresp,
            S_AXI_HP0_0_rvalid  => s_axi_rvalid,
            S_AXI_HP0_0_wdata   => s_axi_wdata,
            S_AXI_HP0_0_wid     => s_axi_wid,
            S_AXI_HP0_0_wlast   => s_axi_wlast,
            S_AXI_HP0_0_wready  => s_axi_wready,
            S_AXI_HP0_0_wstrb   => s_axi_wstrb,
            S_AXI_HP0_0_wvalid  => s_axi_wvalid
        );

    -- Memory-mapped registers.
    inst_registers: entity work.registers
        generic map (
            num_acq_channels    => 2 )
        port map (
            clk                 => clk_adc,
            reset               => s_reset,
            apb_psel            => s_apb_psel,
            apb_penable         => s_apb_penable,
            apb_pwrite          => s_apb_pwrite,
            apb_paddr           => s_apb_paddr,
            apb_pwdata          => s_apb_pwdata,
            apb_pready          => s_apb_pready,
            apb_pslverr         => s_apb_pslverr,
            apb_prdata          => s_apb_prdata,
            reg_control         => s_reg_control,
            reg_status          => s_reg_status
        );

    -- AXI master.
    inst_axi_master: entity work.dma_axi_master
        generic map (
            num_read_channels   => 0,
            num_write_channels  => 2 )
        port map (
            clk                 => clk_adc,
            reset               => s_reset,
            dma_en              => s_reg_control.dma_en,
            dma_busy            => s_reg_status.dma_busy,
            window_base_addr    => s_reg_control.dma_buf_addr,
            window_size         => s_reg_control.dma_buf_size,
            err_read            => s_reg_status.dma_err_read,
            err_write           => s_reg_status.dma_err_write,
            err_address         => s_reg_status.dma_err_address,
            err_any             => s_reg_status.dma_err_any,
            clear_errors        => s_reg_control.dma_clear,
            read_cmd_addr       => (others => (others => '0')),
            read_cmd_length     => (others => (others => '0')),
            read_cmd_valid      => (others => '0'),
            read_cmd_ready      => open,
            read_data           => open,
            read_data_valid     => open,
            write_cmd_addr      => s_dma_write_cmd_addr,
            write_cmd_length    => s_dma_write_cmd_length,
            write_cmd_valid     => s_dma_write_cmd_valid,
            write_cmd_ready     => s_dma_write_cmd_ready,
            write_data          => s_dma_write_data,
            write_data_ready    => s_dma_write_data_ready,
            write_finished      => s_dma_write_finished,
            m_axi_awid          => s_axi_awid,
            m_axi_awaddr        => s_axi_awaddr,
            m_axi_awlen         => s_axi_awlen,
            m_axi_awsize        => s_axi_awsize,
            m_axi_awburst       => s_axi_awburst,
            m_axi_awlock        => s_axi_awlock,
            m_axi_awcache       => s_axi_awcache,
            m_axi_awprot        => s_axi_awprot,
            m_axi_awqos         => s_axi_awqos,
            m_axi_awvalid       => s_axi_awvalid,
            m_axi_awready       => s_axi_awready,
            m_axi_wid           => s_axi_wid,
            m_axi_wdata         => s_axi_wdata,
            m_axi_wstrb         => s_axi_wstrb,
            m_axi_wlast         => s_axi_wlast,
            m_axi_wvalid        => s_axi_wvalid,
            m_axi_wready        => s_axi_wready,
            m_axi_bid           => s_axi_bid,
            m_axi_bresp         => s_axi_bresp,
            m_axi_bvalid        => s_axi_bvalid,
            m_axi_bready        => s_axi_bready,
            m_axi_arid          => s_axi_arid,
            m_axi_araddr        => s_axi_araddr,
            m_axi_arlen         => s_axi_arlen,
            m_axi_arsize        => s_axi_arsize,
            m_axi_arburst       => s_axi_arburst,
            m_axi_arlock        => s_axi_arlock,
            m_axi_arcache       => s_axi_arcache,
            m_axi_arprot        => s_axi_arprot,
            m_axi_arqos         => s_axi_arqos,
            m_axi_arvalid       => s_axi_arvalid,
            m_axi_arready       => s_axi_arready,
            m_axi_rid           => s_axi_rid,
            m_axi_rdata         => s_axi_rdata,
            m_axi_rresp         => s_axi_rresp,
            m_axi_rlast         => s_axi_rlast,
            m_axi_rvalid        => s_axi_rvalid,
            m_axi_rready        => s_axi_rready
    );

    -- DMA write channel for analog acquisition
    inst_acq_dma: entity work.dma_write_channel
        generic map (
            transfer_size_bits  => 4,
            queue_size_bits     => 14,
            idle_timeout        => 256 )
        port map (
            clk                 => clk_adc,
            reset               => s_reset,
            channel_en          => s_reg_control.acq_dma_en,
            channel_busy        => s_reg_status.acq_dma_busy,
            channel_init        => s_reg_control.acq_dma_init,
            addr_start          => s_reg_control.acq_addr_start,
            addr_end            => s_reg_control.acq_addr_end,
            addr_limit          => s_reg_control.acq_addr_limit,
            addr_interrupt      => s_reg_control.acq_addr_intr,
            addr_pointer        => s_reg_status.acq_addr_ptr,
            intr_en             => s_reg_control.acq_intr_en,
            intr_clear          => s_reg_control.acq_intr_clear,
            intr_out            => s_irq_pending(0),
            in_valid            => s_acq_dma_valid,
            in_ready            => s_acq_dma_ready,
            in_empty            => s_acq_dma_empty,
            in_data             => s_acq_dma_data,
            write_cmd_addr      => s_dma_write_cmd_addr(0),
            write_cmd_length    => s_dma_write_cmd_length(0),
            write_cmd_valid     => s_dma_write_cmd_valid(0),
            write_cmd_ready     => s_dma_write_cmd_ready(0),
            write_data          => s_dma_write_data(0),
            write_data_ready    => s_dma_write_data_ready(0),
            write_finished      => s_dma_write_finished(0) );

    -- DMA write channel for time tagger
    inst_tt_dma: entity work.dma_write_channel
        generic map (
            transfer_size_bits  => 4,
            queue_size_bits     => 12,
            idle_timeout        => 256 )
        port map (
            clk                 => clk_adc,
            reset               => s_reset,
            channel_en          => s_reg_control.tt_dma_en,
            channel_busy        => s_reg_status.tt_dma_busy,
            channel_init        => s_reg_control.tt_dma_init,
            addr_start          => s_reg_control.tt_addr_start,
            addr_end            => s_reg_control.tt_addr_end,
            addr_limit          => s_reg_control.tt_addr_limit,
            addr_interrupt      => s_reg_control.tt_addr_intr,
            addr_pointer        => s_reg_status.tt_addr_ptr,
            intr_en             => s_reg_control.tt_intr_en,
            intr_clear          => s_reg_control.tt_intr_clear,
            intr_out            => s_irq_pending(1),
            in_valid            => s_tt_dma_valid,
            in_ready            => s_tt_dma_ready,
            in_empty            => s_tt_dma_empty,
            in_data             => s_tt_dma_data,
            write_cmd_addr      => s_dma_write_cmd_addr(1),
            write_cmd_length    => s_dma_write_cmd_length(1),
            write_cmd_valid     => s_dma_write_cmd_valid(1),
            write_cmd_ready     => s_dma_write_cmd_ready(1),
            write_data          => s_dma_write_data(1),
            write_data_ready    => s_dma_write_data_ready(1),
            write_finished      => s_dma_write_finished(1) );

    -- Timestamp generator.
    inst_timestamp_gen: entity work.timestamp_gen
        port map (
            clk                 => clk_adc,
            reset               => s_reset,
            clear               => s_reg_control.timestamp_clear,
            timestamp           => s_timestamp );

    s_reg_status.timestamp <= s_timestamp;

    -- Capture ADC data.
    -- Ignore the 2 LSB bits which are not-connected on the ADC side.
    inst_capture_gen: for i in 0 to 1 generate
        inst_adc_capture: entity work.adc_capture
            port map (
                clk                 => clk_adc,
                in_data             => adc_dat_i(i)(15 downto 2),
                out_data            => s_adc_data(i) );
    end generate;

    -- Optionally generate simulated ADC samples.
    inst_adc_sample_stream: entity work.adc_sample_stream
        port map (
            clk                 => clk_adc,
            reset               => s_reset,
            simulate            => s_reg_control.simulate_adc,
            in_data             => s_adc_data(0 to 1),
            out_data            => s_adc_sample(0 to 1) );

    -- Monitor range of ADC samples.
    inst_monitor_gen: for i in 0 to 1 generate
        inst_range_monitor: entity work.adc_range_monitor
            generic map (
                signed_data         => false )
            port map (
                clk                 => clk_adc,
                reset               => s_reset,
                clear               => s_reg_control.adc_range_clear,
                in_data             => s_adc_sample(i),
                min_value           => s_reg_status.adc_min_value(i),
                max_value           => s_reg_status.adc_max_value(i) );
    end generate;

    -- Monitor current ADC sample value.
    s_reg_status.adc_sample(0 to 1) <= s_adc_sample(0 to 1);

    -- Drive dummy values to not-implemented channels 2, 3.
    s_reg_status.adc_sample(2 to 3) <= (others => (others => '0'));
    s_reg_status.adc_min_value(2 to 3) <= (others => (others => '0'));
    s_reg_status.adc_max_value(2 to 3) <= (others => (others => '0'));

    -- Analog acquisition data chain.
    inst_acquisition_chain: entity work.acquisition_chain
        generic map (
            num_channels        => 2 )
        port map (
            clk                 => clk_adc,
            reset               => s_reset,
            acquisition_en      => s_reg_control.acquisition_en,
            trigger_delay       => s_reg_control.trigger_delay,
            record_length       => s_reg_control.record_length,
            decimation_factor   => s_reg_control.decimation_factor,
            averaging           => s_reg_control.averaging_en,
            shift_steps         => s_reg_control.shift_steps,
            ch4_mode            => s_reg_control.ch4_mode,
            trig_auto_en        => s_reg_control.trig_auto_en,
            trig_ext_en         => s_reg_control.trig_ext_en,
            trig_ext_once       => s_reg_control.trig_ext_once,
            trig_force          => s_reg_control.trig_force,
            trig_ext_select     => s_reg_control.trig_ext_select,
            trig_ext_falling    => s_reg_control.trig_ext_falling,
            timestamp_in        => s_timestamp,
            adc_data_in         => s_adc_sample,
            trig_ext_in         => s_dig_sample,
            trig_waiting        => s_reg_status.trig_waiting,
            trig_detected       => s_reg_status.trig_detected,
            out_valid           => s_acq_dma_valid,
            out_ready           => s_acq_dma_ready,
            out_empty           => s_acq_dma_empty,
            out_data            => s_acq_dma_data );

    -- Capture digital inputs.
    s_dig_in(0) <= exp_p_io(0);
    s_dig_in(1) <= exp_n_io(0);
    s_dig_in(2) <= exp_p_io(1);
    s_dig_in(3) <= exp_n_io(1);

    inst_dig_capture_gen: for i in 0 to 3 generate

        -- Use a 2-flipflop synchronizer to avoid metastability.
        inst_dig_sync: entity work.syncdff
            port map (
                clk             => clk_adc,
                di              => s_dig_in(i),
                do              => s_dig_sync(i) );

        -- Deglitch filter.
        inst_dig_deglitch: entity work.deglitch
            generic map (
                deglitch_cycles => 4 )
            port map (
                clk             => clk_adc,
                din             => s_dig_sync(i),
                dout            => s_dig_deglitch(i) );

    end generate;

    -- Optionally generate simulated digital signals.
    process (clk_adc) is
    begin
        if rising_edge(clk_adc) then
            if s_reg_control.dig_simulate = '1' then
                s_dig_sample <= s_reg_control.dig_sim_state;
            else
                s_dig_sample <= s_dig_deglitch;
            end if;
        end if;
    end process;

    -- Monitor digital signal state.
    s_reg_status.dig_sample <= s_dig_sample;

    -- Time tagger.
    inst_timetagger: entity work.timetagger
        port map (
            clk                 => clk_adc,
            reset               => s_reset,
            channel_en          => s_reg_control.timetagger_en,
            marker              => s_reg_control.timetagger_mark,
            timestamp_in        => s_timestamp,
            dig_sample          => s_dig_sample,
            out_valid           => s_tt_dma_valid,
            out_ready           => s_tt_dma_ready,
            out_empty           => s_tt_dma_empty,
            out_data            => s_tt_dma_data );

    -- Collect interrupt signals from peripherals and generate interrupt to PS.
    s_reg_status.irq_pending <= s_irq_pending;
    s_irq_f2p(0) <= s_reg_control.irq_enable and or_reduce(s_irq_pending);
    s_irq_f2p(7 downto 1) <= (others => '0');

    -- Blinking LED, 1 Hz.
    process (clk_adc) is
    begin
        if rising_edge(clk_adc) then
            if r_adcclk_cnt = 62499999 then
                r_adcclk_cnt <= (others => '0');
                r_adcclk_led <= not r_adcclk_led;
            else
                r_adcclk_cnt <= r_adcclk_cnt + 1;
            end if;
        end if;
    end process;

end architecture;