spi_flash_ctrl.vhdl

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

library work;
use work.wishbone_types.all;

entity spi_flash_ctrl is
    generic (
        -- Default config for auto-mode
        DEF_CLK_DIV     : natural  := 2;      -- Clock divider SCK = CLK/((CLK_DIV+1)*2)
        DEF_QUAD_READ   : boolean  := false;  -- Use quad read with 8 clk dummy

        -- Dummy clocks after boot
        BOOT_CLOCKS     : boolean  := true;   -- Send 8 dummy clocks after boot

        -- Number of data lines (1=MISO/MOSI, otherwise 2 or 4)
        DATA_LINES      : positive := 1
        );
    port (
        clk : in std_ulogic;
        rst : in std_ulogic;

        -- Wishbone ports:
        wb_in  : in  wb_io_master_out;
        wb_out : out wb_io_slave_out;

        -- Wishbone extra selects
        wb_sel_reg : in std_ulogic;
        wb_sel_map : in std_ulogic;

        -- SPI port
        sck     : out std_ulogic;
        cs_n    : out std_ulogic;
        sdat_o  : out std_ulogic_vector(DATA_LINES-1 downto 0);
        sdat_oe : out std_ulogic_vector(DATA_LINES-1 downto 0);
        sdat_i  : in  std_ulogic_vector(DATA_LINES-1 downto 0)
        );
end entity spi_flash_ctrl;

architecture rtl of spi_flash_ctrl is

    -- Register indices
    constant SPI_REG_BITS       : positive := 3;

    -- Register addresses (matches wishbone addr downto 0, ie, 4 bytes per reg)
    constant SPI_REG_DATA         : std_ulogic_vector(SPI_REG_BITS-1 downto 0) := "000";
    constant SPI_REG_CTRL         : std_ulogic_vector(SPI_REG_BITS-1 downto 0) := "001";
    constant SPI_REG_AUTO_CFG     : std_ulogic_vector(SPI_REG_BITS-1 downto 0) := "010";
    constant SPI_REG_INVALID      : std_ulogic_vector(SPI_REG_BITS-1 downto 0) := "111";

    -- Control register
    signal ctrl_reg    : std_ulogic_vector(15 downto 0);
    alias  ctrl_reset  : std_ulogic is ctrl_reg(0);
    alias  ctrl_cs     : std_ulogic is ctrl_reg(1);
    alias  ctrl_rsrv1  : std_ulogic is ctrl_reg(2);
    alias  ctrl_rsrv2  : std_ulogic is ctrl_reg(3);
    alias  ctrl_div    : std_ulogic_vector(7 downto 0) is ctrl_reg(15 downto 8);

    -- Auto mode config register
    signal auto_cfg_reg     : std_ulogic_vector(29 downto 0);
    alias  auto_cfg_cmd     : std_ulogic_vector(7 downto 0) is auto_cfg_reg(7 downto 0);
    alias  auto_cfg_dummies : std_ulogic_vector(2 downto 0) is auto_cfg_reg(10 downto 8);
    alias  auto_cfg_mode    : std_ulogic_vector(1 downto 0) is auto_cfg_reg(12 downto 11);
    alias  auto_cfg_addr4   : std_ulogic                    is auto_cfg_reg(13);
    alias  auto_cfg_rsrv1   : std_ulogic                    is auto_cfg_reg(14);
    alias  auto_cfg_rsrv2   : std_ulogic                    is auto_cfg_reg(15);
    alias  auto_cfg_div     : std_ulogic_vector(7 downto 0) is auto_cfg_reg(23 downto 16);
    alias  auto_cfg_cstout  : std_ulogic_vector(5 downto 0) is auto_cfg_reg(29 downto 24);

    -- Constants below match top 2 bits of rxtx "mode"
    constant SPI_AUTO_CFG_MODE_SINGLE : std_ulogic_vector(1 downto 0) := "00";
    constant SPI_AUTO_CFG_MODE_DUAL   : std_ulogic_vector(1 downto 0) := "10";
    constant SPI_AUTO_CFG_MODE_QUAD   : std_ulogic_vector(1 downto 0) := "11";

    -- Signals to rxtx
    signal cmd_valid    : std_ulogic;
    signal cmd_clk_div  : natural range 0 to 255;
    signal cmd_mode     : std_ulogic_vector(2 downto 0);
    signal cmd_ready    : std_ulogic;
    signal d_clks       : std_ulogic_vector(2 downto 0);
    signal d_rx         : std_ulogic_vector(7 downto 0);
    signal d_tx         : std_ulogic_vector(7 downto 0);
    signal d_ack        : std_ulogic;
    signal bus_idle     : std_ulogic;

    -- Latch to track that we have a pending read
    signal pending_read : std_ulogic;

    -- Wishbone latches
    signal wb_req       : wb_io_master_out;
    signal wb_stash     : wb_io_master_out;
    signal wb_rsp       : wb_io_slave_out;

    -- Wishbone decode
    signal wb_valid     : std_ulogic;
    signal wb_reg_valid : std_ulogic;
    signal wb_reg_dat_v : std_ulogic;
    signal wb_map_valid : std_ulogic;
    signal wb_reg       : std_ulogic_vector(SPI_REG_BITS-1 downto 0);

    -- Auto mode clock counts XXX FIXME: Look at reasonable values based
    -- on system clock maybe ? Or make them programmable.
    constant CS_DELAY_ASSERT    : integer := 1;   -- CS low to cmd
    constant CS_DELAY_RECOVERY  : integer := 10;  -- CS high to CS low
    constant DEFAULT_CS_TIMEOUT : integer := 32;

    -- Automatic mode state
    type auto_state_t is (AUTO_BOOT, AUTO_IDLE, AUTO_CS_ON, AUTO_CMD,
                          AUTO_ADR0, AUTO_ADR1, AUTO_ADR2, AUTO_ADR3,
                          AUTO_DUMMY,
                          AUTO_DAT0, AUTO_DAT1, AUTO_DAT2, AUTO_DAT3,
                          AUTO_DAT0_DATA, AUTO_DAT1_DATA, AUTO_DAT2_DATA, AUTO_DAT3_DATA,
                          AUTO_SEND_ACK, AUTO_WAIT_REQ, AUTO_RECOVERY);
    -- Automatic mode signals
    signal auto_cs        : std_ulogic;
    signal auto_cmd_valid : std_ulogic;
    signal auto_cmd_mode  : std_ulogic_vector(2 downto 0);
    signal auto_d_txd     : std_ulogic_vector(7 downto 0);
    signal auto_d_clks    : std_ulogic_vector(2 downto 0);
    signal auto_data_next : std_ulogic_vector(wb_out.dat'left downto 0);
    signal auto_cnt_next  : integer range 0 to 63;
    signal auto_ack       : std_ulogic;
    signal auto_next      : auto_state_t;
    signal auto_lad_next  : std_ulogic_vector(31 downto 0);
    signal auto_latch_adr : std_ulogic;

    -- Automatic mode latches
    signal auto_data      : std_ulogic_vector(wb_out.dat'left downto 0);
    signal auto_cnt       : integer range 0 to 63;
    signal auto_state     : auto_state_t;
    signal auto_last_addr : std_ulogic_vector(31 downto 0);

begin

    -- Instanciate low level shifter
    spi_rxtx: entity work.spi_rxtx
        generic map (
            DATA_LINES => DATA_LINES
            )
        port map(
            rst => rst,
            clk => clk,
            clk_div_i => cmd_clk_div,
            cmd_valid_i => cmd_valid,
            cmd_ready_o => cmd_ready,
            cmd_mode_i => cmd_mode,
            cmd_clks_i => d_clks,
            cmd_txd_i => d_tx,
            d_rxd_o => d_rx,
            d_ack_o => d_ack,
            bus_idle_o => bus_idle,
            sck => sck,
            sdat_o => sdat_o,
            sdat_oe => sdat_oe,
            sdat_i => sdat_i
            );

    -- Valid wb command
    wb_valid     <= wb_req.stb and wb_req.cyc;
    wb_reg_valid <= wb_valid and wb_sel_reg;
    wb_map_valid <= wb_valid and wb_sel_map;

    -- Register decode. For map accesses, make it look like "invalid"
    wb_reg       <= wb_req.adr(SPI_REG_BITS - 1 downto 0) when wb_reg_valid else SPI_REG_INVALID;

    -- Shortcut because we test that a lot: data register access
    wb_reg_dat_v <= '1' when wb_reg = SPI_REG_DATA else '0';

    -- Wishbone request -> SPI request
    wb_request_sync: process(clk)
    begin
        if  rising_edge(clk) then
            -- We need to latch whether a read is in progress to block
            -- a subsequent store, otherwise the acks will collide.
            --
            -- We are heavy handed and force a wait for an idle bus if
            -- a store is behind a load. Shouldn't happen with flashes
            -- in practice.
            --
            if cmd_valid = '1' and cmd_ready = '1' then
                pending_read <= not wb_req.we;
            elsif bus_idle = '1' then
                pending_read <= '0'; 
            end if;
        end if;
    end process;

    wb_request_comb: process(all)
    begin
        if ctrl_cs = '1' then
            -- Data register access (see wb_request_sync)
            cmd_valid  <= wb_reg_dat_v and not (pending_read and wb_req.we);

            -- Clock divider from control reg
            cmd_clk_div <= to_integer(unsigned(ctrl_div));

            -- Mode based on sel
            if wb_req.sel = "0010" then
                -- dual mode
                cmd_mode <= "10" & wb_req.we;
                d_clks   <= "011";
            elsif wb_req.sel = "0100" then
                -- quad mode
                cmd_mode <= "11" & wb_req.we;
                d_clks   <= "001";
            else
                -- single bit
                cmd_mode <= "01" & wb_req.we;
                d_clks   <= "111";
            end if;
            d_tx       <= wb_req.dat(7 downto 0);
            cs_n       <= not ctrl_cs;
        else
            cmd_valid   <= auto_cmd_valid;
            cmd_mode    <= auto_cmd_mode;
            cmd_clk_div <= to_integer(unsigned(auto_cfg_div));
            d_tx        <= auto_d_txd;
            d_clks      <= auto_d_clks;
            cs_n        <= not auto_cs;
        end if;
    end process;

    -- Generate wishbone responses
    --
    -- Note: wb_out and wb_in should only appear in this synchronous process
    --
    -- Everything else should work on wb_req and wb_rsp
    wb_response_sync: process(clk)
    begin
        if rising_edge(clk) then
            if rst = '1' then
                wb_out.ack   <= '0';
                wb_out.stall <= '0';
                wb_stash.cyc <= '0';
                wb_stash.stb <= '0';
                wb_stash.sel <= (others => '0');
                wb_stash.we <= '0';
            else
                -- Latch wb responses as well for 1 cycle. Stall is updated
                -- below
                wb_out <= wb_rsp;

                -- Implement a stash buffer. If we are stalled and stash is
                -- free, fill it up. This will generate a WB stall on the
                -- next cycle.
                if wb_rsp.stall = '1' and wb_out.stall = '0' and
                    wb_in.cyc = '1' and wb_in.stb = '1' then
                    wb_stash <= wb_in;
                    wb_out.stall <= '1';
                end if;

                -- We aren't stalled, see what we can do
                if wb_rsp.stall = '0' then
                    if wb_out.stall = '1' then
                        -- Something in stash ! use it and clear stash
                        wb_req <= wb_stash;
                        wb_out.stall <= '0';
                    else
                        -- Nothing in stash, grab request from WB
                        if wb_in.cyc = '1' then
                            wb_req <= wb_in;
                        else
                            wb_req.cyc <= wb_in.cyc;
                            wb_req.stb <= wb_in.stb;
                        end if;
                    end if;
                end if;
            end if;
        end if;
    end process;

    wb_response_comb: process(all)
    begin
        -- Defaults
        wb_rsp.ack <= '0';
        wb_rsp.dat <= x"00" & d_rx & d_rx & d_rx;
        wb_rsp.stall   <= '0';

        -- Depending on the access type...
        if wb_map_valid = '1' then

            -- Memory map access
            wb_rsp.stall <= not auto_ack;  -- XXX FIXME: Allow pipelining
            wb_rsp.ack   <= auto_ack;
            wb_rsp.dat   <= auto_data;

        elsif ctrl_cs = '1' and wb_reg = SPI_REG_DATA then

            -- Data register in manual mode
            --
            -- Stall stores if there's a pending read to avoid
            -- acks colliding. Otherwise accept all accesses
            -- immediately if rxtx is ready.
            --
            -- Note: This must match the logic setting cmd_valid
            -- in wb_request_comb.
            --
            -- We also ack stores immediately when accepted. Loads
            -- are handled separately further down.
            --
            if wb_req.we = '1' and  pending_read = '1' then
                wb_rsp.stall <= '1';
            else
                wb_rsp.ack   <= wb_req.we and cmd_ready;
                wb_rsp.stall <= not cmd_ready;
            end if;

            -- Note: loads acks are handled elsewhere
        elsif wb_reg_valid = '1' then

            -- Normal register access
            --
            -- Normally single cycle but ensure any auto-mode or manual
            -- operation is complete first
            --
            if auto_state = AUTO_IDLE and bus_idle = '1' then
                wb_rsp.ack   <= '1';
                wb_rsp.stall <= '0';

                case wb_reg is
                when SPI_REG_CTRL =>
                    wb_rsp.dat <= (ctrl_reg'range => ctrl_reg, others => '0');
                when SPI_REG_AUTO_CFG =>
                    wb_rsp.dat <= (auto_cfg_reg'range => auto_cfg_reg, others => '0');
                when others => null;
                end case;
            else
                wb_rsp.stall <= '1';
            end if;
        end if;

        -- For loads in manual mode, we've accepted the command early
        -- so none of the above connditions might be true. We thus need
        -- to send the ack whenever we are getting it from rxtx.
        --
        -- This shouldn't collide with any of the above acks because we hold
        -- normal register accesses and stores when there is a pending
        -- load or the bus is busy.
        --
        if ctrl_cs = '1' and d_ack = '1' then
            assert pending_read = '1' report "d_ack without pending read !" severity failure;
            wb_rsp.ack <= '1';
        end if;
    end process;

    -- Automatic mode state machine
    auto_sync: process(clk)
    begin
        if rising_edge(clk) then
            if rst = '1' then
                auto_last_addr <= (others => '0');
                auto_state <= AUTO_BOOT;
                auto_cnt <= 0;
                auto_data  <= (others => '0');
            else
                auto_state <= auto_next;
                auto_cnt   <= auto_cnt_next;
                auto_data  <= auto_data_next;
                if auto_latch_adr = '1' then
                    auto_last_addr <= auto_lad_next;
                end if;
            end if;
        end if;
    end process;

    auto_comb: process(all)
        variable addr : std_ulogic_vector(31 downto 0);
        variable req_is_next : boolean;

        function mode_to_clks(mode: std_ulogic_vector(1 downto 0)) return std_ulogic_vector is
        begin
            if mode = SPI_AUTO_CFG_MODE_QUAD then
                return "001";
            elsif mode = SPI_AUTO_CFG_MODE_DUAL then
                return "011";
            else
                return "111";
            end if;
        end function;
   begin
        -- Default outputs
        auto_ack <= '0';
        auto_cs <= '0';
        auto_cmd_valid <= '0';
        auto_d_txd <= x"00";
        auto_cmd_mode <= "001";
        auto_d_clks <= "111";
        auto_latch_adr <= '0';

        -- Default next state
        auto_next <= auto_state;
        auto_cnt_next <= auto_cnt;
        auto_data_next <= auto_data;

        -- Convert wishbone address into a flash address. We mask
        -- off the 4 top address bits to get rid of the "f" there.
        addr := "00" & wb_req.adr(27 downto 0) & "00";

        -- Calculate the next address for store & compare later
        auto_lad_next <= std_ulogic_vector(unsigned(addr) + 4);

        -- Match incoming request address with next address
        req_is_next := addr = auto_last_addr;

        -- XXX TODO:
        --  - Support < 32-bit accesses

        -- Reset
        if rst = '1' or ctrl_reset = '1' then
            auto_cs <= '0';
            auto_cnt_next <= 0;
            auto_next <= AUTO_BOOT;
        else
            -- Run counter
            if auto_cnt /= 0 then
                auto_cnt_next <= auto_cnt - 1;
            end if;

            -- Automatic CS is set whenever state isn't IDLE or RECOVERY or BOOT
            if  auto_state /= AUTO_IDLE and
                auto_state /= AUTO_RECOVERY and
                auto_state /= AUTO_BOOT then
                auto_cs <= '1';
            end if;

            -- State machine
            case auto_state is
            when AUTO_BOOT =>
                if BOOT_CLOCKS then
                    auto_cmd_valid <= '1';
                    if cmd_ready = '1' then
                        auto_next <= AUTO_IDLE;
                    end if;
                else
                    auto_next <= AUTO_IDLE;
                end if;
            when AUTO_IDLE =>
                -- Access to the memory map only when manual CS isn't set
                if wb_map_valid = '1' and ctrl_cs = '0' then
                    -- Ignore writes, we don't support them yet
                    if wb_req.we = '1' then
                        auto_ack <= '1';
                    else
                        -- Start machine with CS assertion delay
                        auto_next <= AUTO_CS_ON;
                        auto_cnt_next <= CS_DELAY_ASSERT;
                    end if;
                end if;
            when AUTO_CS_ON =>
                if auto_cnt = 0 then
                    -- CS asserted long enough, send command
                    auto_next <= AUTO_CMD;
                end if;
            when AUTO_CMD =>
                auto_d_txd <= auto_cfg_cmd;
                auto_cmd_valid <= '1';
                if cmd_ready = '1' then
                    if auto_cfg_addr4 = '1' then
                        auto_next <= AUTO_ADR3;
                    else
                        auto_next <= AUTO_ADR2;
                    end if;
                end if;
            when AUTO_ADR3 =>
                auto_d_txd <= addr(31 downto 24);
                auto_cmd_valid <= '1';
                if cmd_ready = '1' then
                    auto_next <= AUTO_ADR2;
                end if;
            when AUTO_ADR2 =>
                auto_d_txd <= addr(23 downto 16);
                auto_cmd_valid <= '1';
                if cmd_ready = '1' then
                    auto_next <= AUTO_ADR1;
                end if;
            when AUTO_ADR1 =>
                auto_d_txd <= addr(15 downto 8);
                auto_cmd_valid <= '1';
                if cmd_ready = '1' then
                    auto_next <= AUTO_ADR0;
                end if;
            when AUTO_ADR0 =>
                auto_d_txd <= addr(7 downto 0);
                auto_cmd_valid <= '1';
                if cmd_ready = '1' then
                    if auto_cfg_dummies = "000" then
                        auto_next <= AUTO_DAT0;
                    else
                        auto_next <= AUTO_DUMMY;
                    end if;
                end if;
            when AUTO_DUMMY =>
                auto_cmd_valid <= '1';
                auto_d_clks <= auto_cfg_dummies;
                if cmd_ready = '1' then
                    auto_next <= AUTO_DAT0;
                end if;
            when AUTO_DAT0 =>
                auto_cmd_valid <= '1';
                auto_cmd_mode <= auto_cfg_mode & "0";
                auto_d_clks <= mode_to_clks(auto_cfg_mode);
                if cmd_ready = '1' then
                    auto_next <= AUTO_DAT0_DATA;
                end if;
            when AUTO_DAT0_DATA =>
                if d_ack = '1' then
                    auto_data_next(7 downto 0) <= d_rx;
                    auto_next <= AUTO_DAT1;
                end if;
            when AUTO_DAT1 =>
                auto_cmd_valid <= '1';
                auto_cmd_mode <= auto_cfg_mode & "0";
                auto_d_clks <= mode_to_clks(auto_cfg_mode);
                if cmd_ready = '1' then
                    auto_next <= AUTO_DAT1_DATA;
                end if;
            when AUTO_DAT1_DATA =>
                if d_ack = '1' then
                    auto_data_next(15 downto 8) <= d_rx;
                    auto_next <= AUTO_DAT2;
                end if;
            when AUTO_DAT2 =>
                auto_cmd_valid <= '1';
                auto_cmd_mode <= auto_cfg_mode & "0";
                auto_d_clks <= mode_to_clks(auto_cfg_mode);
                if cmd_ready = '1' then
                    auto_next <= AUTO_DAT2_DATA;
                end if;
            when AUTO_DAT2_DATA =>
                if d_ack = '1' then
                    auto_data_next(23 downto 16) <= d_rx;
                    auto_next <= AUTO_DAT3;
                end if;
            when AUTO_DAT3 =>
                auto_cmd_valid <= '1';
                auto_cmd_mode <= auto_cfg_mode & "0";
                auto_d_clks <= mode_to_clks(auto_cfg_mode);
                if cmd_ready = '1' then
                    auto_next <= AUTO_DAT3_DATA;
                end if;
            when AUTO_DAT3_DATA =>
                if d_ack = '1' then
                    auto_data_next(31 downto 24) <= d_rx;
                    auto_next <= AUTO_SEND_ACK;
                    auto_latch_adr <= '1';
                end if;
            when AUTO_SEND_ACK =>
                auto_ack <= '1';
                auto_cnt_next <= to_integer(unsigned(auto_cfg_cstout));
                auto_next <= AUTO_WAIT_REQ;
            when AUTO_WAIT_REQ =>
                -- Incoming bus request we can take ? Otherwise do we need
                -- to cancel the wait ?
                if wb_map_valid = '1' and req_is_next and wb_req.we = '0' then
                    auto_next <= AUTO_DAT0;
                elsif wb_map_valid = '1' or wb_reg_valid = '1' or auto_cnt = 0 then
                    -- This means we can drop the CS right on the next clock.
                    -- We make the assumption here that the two cycles min
                    -- spent in AUTO_SEND_ACK and AUTO_WAIT_REQ are long enough
                    -- to deassert CS. If that doesn't hold true in the future,
                    -- add another state.
                    auto_cnt_next <= CS_DELAY_RECOVERY;
                    auto_next <= AUTO_RECOVERY;
                end if; 
            when AUTO_RECOVERY =>
                if auto_cnt = 0 then
                    auto_next <= AUTO_IDLE;
                end if;
            end case;
        end if;
    end process;

    -- Register write sync machine
    reg_write: process(clk)
        function reg_wr(r : in std_ulogic_vector;
                        w : in wb_io_master_out) return std_ulogic_vector is
            variable b : natural range 0 to 31;
            variable t : std_ulogic_vector(r'range);
        begin
            t := r;
            for i in r'range loop
                if w.sel(i/8) = '1' then
                    t(i) := w.dat(i);
                end if;
            end loop;
            return t;
        end function;
    begin
        if rising_edge(clk) then
            -- Reset auto-clear
            if rst = '1' or ctrl_reset = '1' then
                ctrl_reset       <= '0';
                ctrl_cs          <= '0';
                ctrl_rsrv1       <= '0';
                ctrl_rsrv2       <= '0';
                ctrl_div         <= std_ulogic_vector(to_unsigned(DEF_CLK_DIV, 8));
                if DEF_QUAD_READ then
                    auto_cfg_cmd     <= x"6b";
                    auto_cfg_dummies <= "111";
                    auto_cfg_mode    <= SPI_AUTO_CFG_MODE_QUAD;
                else
                    auto_cfg_cmd     <= x"03";
                    auto_cfg_dummies <= "000";
                    auto_cfg_mode    <= SPI_AUTO_CFG_MODE_SINGLE;
                end if;
                auto_cfg_addr4   <= '0';
                auto_cfg_rsrv1   <= '0';
                auto_cfg_rsrv2   <= '0';
                auto_cfg_div     <= std_ulogic_vector(to_unsigned(DEF_CLK_DIV, 8));
                auto_cfg_cstout  <= std_ulogic_vector(to_unsigned(DEFAULT_CS_TIMEOUT, 6));
            end if;

            if wb_reg_valid = '1' and wb_req.we = '1' and auto_state = AUTO_IDLE and bus_idle = '1' then
                if wb_reg = SPI_REG_CTRL then
                    ctrl_reg     <= reg_wr(ctrl_reg, wb_req);
                end if;
                if wb_reg = SPI_REG_AUTO_CFG then
                    auto_cfg_reg <= reg_wr(auto_cfg_reg, wb_req);
                end if;
            end if;
        end if;
    end process;

end architecture;