--
--  Format analog acquisition data into a stream of 64-bit words.
--
--  Joris van Rantwijk 2024
--

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

use work.puzzlefw_pkg.all;


entity acquisition_stream is

    generic (
        -- Number of analog input channels. It should be either 2 or 4.
        num_channels:       integer range 2 to 4
    );

    port (
        -- Main clock, active on rising edge.
        clk:                in  std_logic;

        -- Reset, active high, synchronous to main clock.
        reset:              in  std_logic;

        -- High to enable 4-channel mode.
        -- Ignored if num_channels == 2.
        ch4_mode:           in  std_logic;

        -- Global timestamp counter.
        timestamp_in:       in  std_logic_vector(timestamp_bits - 1 downto 0);

        -- High for one cycle when a trigger occurs.
        trig_ack:           in  std_logic;

        -- Decimated sample stream.
        sample_valid:       in  std_logic;
        sample_data:        in  sample_data_array(0 to num_channels - 1);

        -- Output data stream.
        out_valid:          out std_logic;
        out_ready:          in  std_logic;
        out_empty:          in  std_logic;
        out_data:           out dma_data_type
    );

end entity;

architecture arch of acquisition_stream is

    type regs_type is record
        overflow:           std_logic;
        trig_pending:       std_logic;
        trig_timestamp:     std_logic_vector(timestamp_bits - 1 downto 0);
        sample_pending:     std_logic;
        sample_data:        sample_data_array(0 to num_channels - 3);
        out_valid:          std_logic;
        out_data:           dma_data_type;
    end record;

    constant regs_init: regs_type := (
        overflow            => '0',
        trig_pending        => '0',
        trig_timestamp      => (others => '0'),
        sample_pending      => '0',
        sample_data         => (others => (others => '0')),
        out_valid           => '0',
        out_data            => (others => '0')
    );

    signal r: regs_type := regs_init;
    signal rnext: regs_type;

begin

    -- Drive output ports.
    out_valid           <= r.out_valid;
    out_data            <= r.out_data;

    --
    -- Combinatorial process.
    --
    process (all) is
        variable v: regs_type;
    begin
        -- Load current register values.
        v := r;

        -- By default, do not emit data.
        v.out_valid := '0';

        if sample_valid = '1' then

            -- Emit first sample data word.
            v.out_valid := '1';
            v.out_data(63 downto 56) := msg_adc_data;
            v.out_data(55 downto 48) := x"10";
            v.out_data(23 downto 0) := sample_data(0);
            v.out_data(47 downto 24) := sample_data(1);

            -- Detect internal overflow.
            if (r.sample_pending = '1') or (r.trig_pending = '1') then
                v.overflow := '1';
            end if;

        elsif r.sample_pending = '1' then

            -- Emit second sample data word.
            v.sample_pending := '0';
            v.out_valid := '1';
            v.out_data(63 downto 56) := msg_adc_data;
            v.out_data(55 downto 48) := x"32";
            v.out_data(47 downto 0) := (others => '0');
            if num_channels > 2 then
                v.out_data(23 downto 0) := r.sample_data(0);
            end if;
            if num_channels > 3 then
                v.out_data(47 downto 24) := r.sample_data(1);
            end if;

        elsif r.trig_pending = '1' then

            -- Emit pending trigger record.
            v.trig_pending := '0';
            v.out_valid := '1';
            v.out_data(63 downto 56) := msg_trigger;
            v.out_data(55 downto 48) := x"00";
            v.out_data(47 downto 0) := r.trig_timestamp;

        elsif trig_ack = '1' then

            -- Emit trigger record.
            v.out_valid := '1';
            v.out_data(63 downto 56) := msg_trigger;
            v.out_data(55 downto 48) := x"00";
            v.out_data(47 downto 0) := timestamp_in;

        end if;

        -- Latch second sample data word.
        if (num_channels > 2) and (sample_valid = '1') then
            v.sample_pending := ch4_mode;
            v.sample_data := sample_data(2 to num_channels - 1);
        end if;

        -- Latch timestamp when a trigger occurs.
        if trig_ack = '1' then
            v.trig_timestamp := timestamp_in;
            if (sample_valid = '1') or (r.sample_pending = '1') then
                v.trig_pending := '1';
            end if;

            -- Detect internal overflow.
            if r.trig_pending = '1' then
                v.overflow := '1';
            end if;
        end if;

        -- Detect overflow of external data buffer.
        if (r.out_valid = '1') and (out_ready = '0') then
            v.overflow := '1';
            v.out_valid := '0';
        end if;

        -- If there is a pending overflow, discard data until the buffer
        -- is empty, then emit an overflow record.
        if r.overflow = '1' then
            v.sample_pending := '0';
            v.trig_pending := '0';
            v.out_valid := '0';
            v.out_data(63 downto 56) := msg_overflow;
            v.out_data(55 downto 0) := (others => '0');

            if out_empty = '1' then
                v.out_valid := '1';
                v.overflow := '0';
            end if;
        end if;

        -- Synchronous reset.
        if reset = '1' then
            v := regs_init;
        end if;

        -- Drive new register values to synchronous process.
        rnext <= v;
    
    end process;

    --
    -- Synchronous process.
    --
    process (clk) is
    begin
        if rising_edge(clk) then
            r <= rnext;
        end if;
    end process;

end architecture;