Subversion Repositories neorv32

-- #################################################################################################

-- # << NEORV32 - Default Processor Testbench >>                                                   #

-- # ********************************************************************************************* #

-- # The processor is configured to use a maximum of functional units (for testing purpose).       #

-- # Use the "User Configuration" section to configure the testbench according to your needs.      #

-- # See NEORV32 data sheet for more information.                                                  #

-- # ********************************************************************************************* #

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2021, Stephan Nolting. All rights reserved.                                     #

-- #                                                                                               #

-- # Redistribution and use in source and binary forms, with or without modification, are          #

-- # permitted provided that the following conditions are met:                                     #

-- #                                                                                               #

-- # 1. Redistributions of source code must retain the above copyright notice, this list of        #

-- #    conditions and the following disclaimer.                                                   #

-- #                                                                                               #

-- # 2. Redistributions in binary form must reproduce the above copyright notice, this list of     #

-- #    conditions and the following disclaimer in the documentation and/or other materials        #

-- #    provided with the distribution.                                                            #

-- #                                                                                               #

-- # 3. Neither the name of the copyright holder nor the names of its contributors may be used to  #

-- #    endorse or promote products derived from this software without specific prior written      #

-- #    permission.                                                                                #

-- #                                                                                               #

-- # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS   #

-- # OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF               #

-- # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE    #

-- # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,     #

-- # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE #

-- # GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED    #

-- # AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING     #

-- # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED  #

-- # OF THE POSSIBILITY OF SUCH DAMAGE.                                                            #

-- # ********************************************************************************************* #

-- # The NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #

-- #################################################################################################

library vunit_lib;

context vunit_lib.vunit_context;

context vunit_lib.com_context;

context vunit_lib.vc_context;

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use ieee.math_real.all;

library neorv32;

use neorv32.neorv32_package.all;

use neorv32.neorv32_application_image.all; -- this file is generated by the image generator

use std.textio.all;

library osvvm;

use osvvm.RandomPkg.all;

use work.uart_rx_pkg.all;

entity neorv32_tb is

  generic (runner_cfg : string := runner_cfg_default;

           ci_mode : boolean := false);

end neorv32_tb;

architecture neorv32_tb_rtl of neorv32_tb is

  -- User Configuration ---------------------------------------------------------------------

  -- -------------------------------------------------------------------------------------------

  -- general --

  constant ext_imem_c              : boolean := false; -- false: use and boot from proc-internal IMEM, true: use and boot from external (initialized) simulated IMEM (ext. mem A)

  constant ext_dmem_c              : boolean := false; -- false: use proc-internal DMEM, true: use external simulated DMEM (ext. mem B)

  constant imem_size_c             : natural := 16*1024; -- size in bytes of processor-internal IMEM / external mem A

  constant dmem_size_c             : natural := 8*1024; -- size in bytes of processor-internal DMEM / external mem B

  constant f_clock_c               : natural := 100000000; -- main clock in Hz

  constant baud0_rate_c            : natural := 19200; -- simulation UART0 (primary UART) baud rate

  constant baud1_rate_c            : natural := 19200; -- simulation UART1 (secondary UART) baud rate

  -- simulated external Wishbone memory A (can be used as external IMEM) --

  constant ext_mem_a_base_addr_c   : std_ulogic_vector(31 downto 0) := x"00000000"; -- wishbone memory base address (external IMEM base)

  constant ext_mem_a_size_c        : natural := imem_size_c; -- wishbone memory size in bytes

  constant ext_mem_a_latency_c     : natural := 8; -- latency in clock cycles (min 1, max 255), plus 1 cycle initial delay

  -- simulated external Wishbone memory B (can be used as external DMEM) --

  constant ext_mem_b_base_addr_c   : std_ulogic_vector(31 downto 0) := x"80000000"; -- wishbone memory base address (external DMEM base)

  constant ext_mem_b_size_c        : natural := dmem_size_c; -- wishbone memory size in bytes

  constant ext_mem_b_latency_c     : natural := 8; -- latency in clock cycles (min 1, max 255), plus 1 cycle initial delay

  -- simulated external Wishbone memory C (can be used to simulate external IO access) --

  constant ext_mem_c_base_addr_c   : std_ulogic_vector(31 downto 0) := x"F0000000"; -- wishbone memory base address (default begin of EXTERNAL IO area)

  constant ext_mem_c_size_c        : natural := 64; -- wishbone memory size in bytes

  constant ext_mem_c_latency_c     : natural := 3; -- latency in clock cycles (min 1, max 255), plus 1 cycle initial delay

  -- simulation interrupt trigger --

  constant irq_trigger_base_addr_c : std_ulogic_vector(31 downto 0) := x"FF000000";

  -- -------------------------------------------------------------------------------------------

  -- internals - hands off! --

  constant int_imem_c       : boolean := not ext_imem_c;

  constant int_dmem_c       : boolean := not ext_dmem_c;

  constant uart0_baud_val_c : real := real(f_clock_c) / real(baud0_rate_c);

  constant uart1_baud_val_c : real := real(f_clock_c) / real(baud1_rate_c);

  constant t_clock_c        : time := (1 sec) / f_clock_c;

  -- generators --

  signal clk_gen, rst_gen : std_ulogic := '0';

  -- uart --

  signal uart0_txd : std_ulogic; -- local loop-back

  signal uart0_cts : std_ulogic; -- local loop-back

  signal uart1_txd : std_ulogic; -- local loop-back

  signal uart1_cts : std_ulogic; -- local loop-back

  -- gpio --

  signal gpio : std_ulogic_vector(63 downto 0);

  -- twi --

  signal twi_scl, twi_sda : std_logic;

  -- spi --

  signal spi_data : std_ulogic;

  -- irq --

  signal msi_ring, mei_ring, nmi_ring : std_ulogic;

  -- Wishbone bus --

  type wishbone_t is record

    addr  : std_ulogic_vector(31 downto 0); -- address

    wdata : std_ulogic_vector(31 downto 0); -- master write data

    rdata : std_ulogic_vector(31 downto 0); -- master read data

    we    : std_ulogic; -- write enable

    sel   : std_ulogic_vector(03 downto 0); -- byte enable

    stb   : std_ulogic; -- strobe

    cyc   : std_ulogic; -- valid cycle

    ack   : std_ulogic; -- transfer acknowledge

    err   : std_ulogic; -- transfer error

    tag   : std_ulogic_vector(02 downto 0); -- request tag

    lock  : std_ulogic; -- exclusive access request

  end record;

  signal wb_cpu, wb_mem_a, wb_mem_b, wb_mem_c, wb_irq : wishbone_t;

  -- Wishbone access latency type --

  type ext_mem_read_latency_t is array (0 to 255) of std_ulogic_vector(31 downto 0);

  -- exclusive access / reservation --

  signal ext_mem_c_atomic_reservation : std_ulogic := '0';

  -- simulated external memory c (IO) --

  signal ext_ram_c : mem32_t(0 to ext_mem_c_size_c/4-1); -- uninitialized, used to simulate external IO

  -- simulated external memory bus feedback type --

  type ext_mem_t is record

    rdata  : ext_mem_read_latency_t;

    acc_en : std_ulogic;

    ack    : std_ulogic_vector(ext_mem_a_latency_c-1 downto 0);

  end record;

  signal ext_mem_a, ext_mem_b, ext_mem_c : ext_mem_t;

  -- stream link interface - local echo --

  signal slink_dat : sdata_8x32_t;

  signal slink_val : std_ulogic_vector(7 downto 0);

  signal slink_rdy : std_ulogic_vector(7 downto 0);

  signal slink_transmitter_dat, slink_receiver_dat : sdata_8x32_t;

  signal slink_transmitter_val, slink_receiver_val : std_ulogic_vector(7 downto 0);

  signal slink_transmitter_rdy, slink_receiver_rdy : std_ulogic_vector(7 downto 0);

  constant uart0_rx_logger : logger_t := get_logger("UART0.RX");

  constant uart1_rx_logger : logger_t := get_logger("UART1.RX");

  constant uart0_rx_handle : uart_rx_t := new_uart_rx(uart0_baud_val_c, uart0_rx_logger);

  constant uart1_rx_handle : uart_rx_t := new_uart_rx(uart1_baud_val_c, uart1_rx_logger);

  type axi_stream_master_vec_t is array(integer range <>) of axi_stream_master_t;

  type axi_stream_slave_vec_t is array(integer range <>) of axi_stream_slave_t;

  impure function init_slink_transmitters return axi_stream_master_vec_t is

    variable result : axi_stream_master_vec_t(slink_transmitter_val'range);

  begin

    for idx in result'range loop

      result(idx) := new_axi_stream_master(

        data_length => slink_transmitter_dat(idx)'length,

        stall_config => new_stall_config(0.05, 1, 10)

      );

    end loop;

    return result;

  end;

  impure function init_slink_receivers return axi_stream_slave_vec_t is

    variable result : axi_stream_slave_vec_t(slink_receiver_val'range);

  begin

    for idx in result'range loop

      result(idx) := new_axi_stream_slave(

        data_length => slink_receiver_dat(idx)'length,

        stall_config => new_stall_config(0.05, 1, 10)

      );

    end loop;

    return result;

  end;

  constant slink_transmitters : axi_stream_master_vec_t := init_slink_transmitters;

  constant slink_receivers : axi_stream_slave_vec_t := init_slink_receivers;

begin

  test_runner : process

    variable msg : msg_t;

    variable rnd : RandomPType;

    variable value : std_logic_vector(slink_transmitter_dat(0)'range);

  begin

    test_runner_setup(runner, runner_cfg);

    rnd.InitSeed(test_runner'path_name);

    -- Show passing checks for UART0 on the display (stdout)

    show(uart0_rx_logger, display_handler, pass);

    show(uart1_rx_logger, display_handler, pass);

    if ci_mode then

      check_uart(net, uart0_rx_handle, nul & nul);

    else

      check_uart(net, uart0_rx_handle, "Blinking LED demo program" & cr & lf);

    end if;

    if ci_mode then

      -- No need to send the full expectation in one big chunk

      check_uart(net, uart1_rx_handle, nul & nul);

      check_uart(net, uart1_rx_handle, "0/46" & cr & lf);

    end if;

    -- Apply some random data on each SLINK inputs and expect it to

    -- be echoed by the CPU. No blocking. Let the SLINK transmitters

    -- and receivers do this work in parallel.

    for idx in slink_transmitters'range loop

      for iter in 1 to 100 loop

        value := rnd.RandSlv(value'length);

        -- SLINK is AXI Stream compatible so the SLINK transmitters and

        -- and receivers are AXI Stream master and slave verification components (VCs).

        -- The full-featured AXI Stream verification component interface (VCI) is used

        -- but the AXI stream VCs also implements the basic stream VCI which also works

        -- for simple transactions like these. To use that interface for pushing data

        -- the AXI Steam VC must be "cast" to a basic stream VC using "as_stream"

        --

        -- push_stream(net, as_stream(slink_transmitters(idx)), value);

        push_axi_stream(net, slink_transmitters(idx), value);

        check_axi_stream(net, slink_receivers(idx), value, blocking => false);

      end loop;

    end loop;

    -- Wait until all expected data has been received

    --

    -- wait_until_idle can take the VC actor as argument but

    -- the more abstract view is that wait_until_idle is part

    -- of the sync VCI and to use it a VC must be cast

    -- to a sync VC

    wait_until_idle(net, as_sync(uart0_rx_handle));

    wait_until_idle(net, as_sync(uart1_rx_handle));

    for idx in slink_receivers'range loop

      wait_until_idle(net, as_sync(slink_receivers(idx)));

    end loop;

    -- Wait a bit more if some extra unexpected data is produced. If so,

    -- uart_rx will fail

    wait for (20 * (1e9 / baud0_rate_c)) * ns;

    test_runner_cleanup(runner);

  end process;

  -- In case we get stuck waiting there is a watchdog timeout to terminate and fail the

  -- testbench

  test_runner_watchdog(runner, 50 ms);

  -- Clock/Reset Generator ------------------------------------------------------------------

  -- -------------------------------------------------------------------------------------------

  clk_gen <= not clk_gen after (t_clock_c/2);

  rst_gen <= '0', '1' after 60*(t_clock_c/2);

  -- The Core of the Problem ----------------------------------------------------------------

  -- -------------------------------------------------------------------------------------------

  neorv32_top_inst: neorv32_top

  generic map (

    -- General --

    CLOCK_FREQUENCY              => f_clock_c,     -- clock frequency of clk_i in Hz

    HW_THREAD_ID                 => 0,             -- hardware thread id (hartid) (32-bit)

    INT_BOOTLOADER_EN            => false,         -- boot configuration: true = boot explicit bootloader; false = boot from int/ext (I)MEM

    -- On-Chip Debugger (OCD) --

    ON_CHIP_DEBUGGER_EN          => true,          -- implement on-chip debugger

    -- RISC-V CPU Extensions --

    CPU_EXTENSION_RISCV_A        => true,          -- implement atomic extension?

    CPU_EXTENSION_RISCV_C        => true,          -- implement compressed extension?

    CPU_EXTENSION_RISCV_E        => false,         -- implement embedded RF extension?

    CPU_EXTENSION_RISCV_M        => true,          -- implement muld/div extension?

    CPU_EXTENSION_RISCV_U        => true,          -- implement user mode extension?

    CPU_EXTENSION_RISCV_Zbb      => true,          -- implement basic bit-manipulation sub-extension?

    CPU_EXTENSION_RISCV_Zfinx    => true,          -- implement 32-bit floating-point extension (using INT reg!)

    CPU_EXTENSION_RISCV_Zicsr    => true,          -- implement CSR system?

    CPU_EXTENSION_RISCV_Zifencei => true,          -- implement instruction stream sync.?

    -- Extension Options --

    FAST_MUL_EN                  => false,         -- use DSPs for M extension's multiplier

    FAST_SHIFT_EN                => false,         -- use barrel shifter for shift operations

    CPU_CNT_WIDTH                => 64,            -- total width of CPU cycle and instret counters (0..64)

    -- Physical Memory Protection (PMP) --

    PMP_NUM_REGIONS              => 5,             -- number of regions (0..64)

    PMP_MIN_GRANULARITY          => 64*1024,       -- minimal region granularity in bytes, has to be a power of 2, min 8 bytes

    -- Hardware Performance Monitors (HPM) --

    HPM_NUM_CNTS                 => 12,            -- number of implemented HPM counters (0..29)

    HPM_CNT_WIDTH                => 40,            -- total size of HPM counters (0..64)

    -- Internal Instruction memory --

    MEM_INT_IMEM_EN              => int_imem_c ,   -- implement processor-internal instruction memory

    MEM_INT_IMEM_SIZE            => imem_size_c,   -- size of processor-internal instruction memory in bytes

    -- Internal Data memory --

    MEM_INT_DMEM_EN              => int_dmem_c,    -- implement processor-internal data memory

    MEM_INT_DMEM_SIZE            => dmem_size_c,   -- size of processor-internal data memory in bytes

    -- Internal Cache memory --

    ICACHE_EN                    => true,          -- implement instruction cache

    ICACHE_NUM_BLOCKS            => 8,             -- i-cache: number of blocks (min 2), has to be a power of 2

    ICACHE_BLOCK_SIZE            => 64,            -- i-cache: block size in bytes (min 4), has to be a power of 2

    ICACHE_ASSOCIATIVITY         => 2,             -- i-cache: associativity / number of sets (1=direct_mapped), has to be a power of 2

    -- External memory interface --

    MEM_EXT_EN                   => true,          -- implement external memory bus interface?

    MEM_EXT_TIMEOUT              => 255,           -- cycles after a pending bus access auto-terminates (0 = disabled)

    -- Stream link interface --

    SLINK_NUM_TX                 => 8,             -- number of TX links (0..8)

    SLINK_NUM_RX                 => 8,             -- number of TX links (0..8)

    SLINK_TX_FIFO                => 4,             -- TX fifo depth, has to be a power of two

    SLINK_RX_FIFO                => 1,             -- RX fifo depth, has to be a power of two

    -- External Interrupts Controller (XIRQ) --

    XIRQ_NUM_CH                  => 32,            -- number of external IRQ channels (0..32)

    XIRQ_TRIGGER_TYPE            => (others => '1'), -- trigger type: 0=level, 1=edge

    XIRQ_TRIGGER_POLARITY        => (others => '1'), -- trigger polarity: 0=low-level/falling-edge, 1=high-level/rising-edge 

    -- Processor peripherals --

    IO_GPIO_EN                   => true,          -- implement general purpose input/output port unit (GPIO)?

    IO_MTIME_EN                  => true,          -- implement machine system timer (MTIME)?

    IO_UART0_EN                  => true,          -- implement primary universal asynchronous receiver/transmitter (UART0)?

    IO_UART1_EN                  => true,          -- implement secondary universal asynchronous receiver/transmitter (UART1)?

    IO_SPI_EN                    => true,          -- implement serial peripheral interface (SPI)?

    IO_TWI_EN                    => true,          -- implement two-wire interface (TWI)?

    IO_PWM_NUM_CH                => 30,            -- number of PWM channels to implement (0..60); 0 = disabled

    IO_WDT_EN                    => true,          -- implement watch dog timer (WDT)?

    IO_TRNG_EN                   => false,         -- trng cannot be simulated

    IO_CFS_EN                    => true,          -- implement custom functions subsystem (CFS)?

    IO_CFS_CONFIG                => (others => '0'), -- custom CFS configuration generic

    IO_CFS_IN_SIZE               => 32,            -- size of CFS input conduit in bits

    IO_CFS_OUT_SIZE              => 32,            -- size of CFS output conduit in bits

    IO_NEOLED_EN                 => true           -- implement NeoPixel-compatible smart LED interface (NEOLED)?

  )

  port map (

    -- Global control --

    clk_i          => clk_gen,         -- global clock, rising edge

    rstn_i         => rst_gen,         -- global reset, low-active, async

    -- JTAG on-chip debugger interface (available if ON_CHIP_DEBUGGER_EN = true) --

    jtag_trst_i    => '1',             -- low-active TAP reset (optional)

    jtag_tck_i     => '0',             -- serial clock

    jtag_tdi_i     => '0',             -- serial data input

    jtag_tdo_o     => open,            -- serial data output

    jtag_tms_i     => '0',             -- mode select

    -- Wishbone bus interface (available if MEM_EXT_EN = true) --

    wb_tag_o       => wb_cpu.tag,      -- request tag

    wb_adr_o       => wb_cpu.addr,     -- address

    wb_dat_i       => wb_cpu.rdata,    -- read data

    wb_dat_o       => wb_cpu.wdata,    -- write data

    wb_we_o        => wb_cpu.we,       -- read/write

    wb_sel_o       => wb_cpu.sel,      -- byte enable

    wb_stb_o       => wb_cpu.stb,      -- strobe

    wb_cyc_o       => wb_cpu.cyc,      -- valid cycle

    wb_lock_o      => wb_cpu.lock,     -- exclusive access request

    wb_ack_i       => wb_cpu.ack,      -- transfer acknowledge

    wb_err_i       => wb_cpu.err,      -- transfer error

    -- Advanced memory control signals (available if MEM_EXT_EN = true) --

    fence_o        => open,            -- indicates an executed FENCE operation

    fencei_o       => open,            -- indicates an executed FENCEI operation

    -- TX stream interfaces (available if SLINK_NUM_TX > 0) --

    slink_tx_dat_o => slink_dat,       -- output data

    slink_tx_val_o => slink_val,       -- valid output

    slink_tx_rdy_i => slink_rdy,       -- ready to send

    -- RX stream interfaces (available if SLINK_NUM_RX > 0) --

    slink_rx_dat_i => slink_dat,       -- input data

    slink_rx_val_i => slink_val,       -- valid input

    slink_rx_rdy_o => slink_rdy,       -- ready to receive

    -- GPIO (available if IO_GPIO_EN = true) --

    gpio_o         => gpio,            -- parallel output

    gpio_i         => gpio,            -- parallel input

    -- primary UART0 (available if IO_UART0_EN = true) --

    uart0_txd_o    => uart0_txd,       -- UART0 send data

    uart0_rxd_i    => uart0_txd,       -- UART0 receive data

    uart0_rts_o    => uart0_cts,       -- hw flow control: UART0.RX ready to receive ("RTR"), low-active, optional

    uart0_cts_i    => uart0_cts,       -- hw flow control: UART0.TX allowed to transmit, low-active, optional

    -- secondary UART1 (available if IO_UART1_EN = true) --

    uart1_txd_o    => uart1_txd,       -- UART1 send data

    uart1_rxd_i    => uart1_txd,       -- UART1 receive data

    uart1_rts_o    => uart1_cts,       -- hw flow control: UART1.RX ready to receive ("RTR"), low-active, optional

    uart1_cts_i    => uart1_cts,       -- hw flow control: UART1.TX allowed to transmit, low-active, optional

    -- SPI (available if IO_SPI_EN = true) --

    spi_sck_o      => open,            -- SPI serial clock

    spi_sdo_o      => spi_data,        -- controller data out, peripheral data in

    spi_sdi_i      => spi_data,        -- controller data in, peripheral data out

    spi_csn_o      => open,            -- SPI CS

    -- TWI (available if IO_TWI_EN = true) --

    twi_sda_io     => twi_sda,         -- twi serial data line

    twi_scl_io     => twi_scl,         -- twi serial clock line

    -- PWM (available if IO_PWM_NUM_CH > 0) --

    pwm_o          => open,            -- pwm channels

    -- Custom Functions Subsystem IO --

    cfs_in_i       => (others => '0'), -- custom CFS inputs

    cfs_out_o      => open,            -- custom CFS outputs

    -- NeoPixel-compatible smart LED interface (available if IO_NEOLED_EN = true) --

    neoled_o       => open,            -- async serial data line

    -- System time --

    mtime_i        => (others => '0'), -- current system time from ext. MTIME (if IO_MTIME_EN = false)

    mtime_o        => open,            -- current system time from int. MTIME (if IO_MTIME_EN = true)

    -- External platform interrupts (available if XIRQ_NUM_CH > 0) --

    xirq_i         => gpio(31 downto 0), -- IRQ channels

    -- CPU Interrupts --

    nm_irq_i       => nmi_ring,        -- non-maskable interrupt

    mtime_irq_i    => '0',             -- machine software interrupt, available if IO_MTIME_EN = false

    msw_irq_i      => msi_ring,        -- machine software interrupt

    mext_irq_i     => mei_ring         -- machine external interrupt

  );

  -- TWI termination (pull-ups) --

  twi_scl <= 'H';

  twi_sda <= 'H';

  uart0_checker: entity work.uart_rx

    generic map (uart0_rx_handle)

    port map (

      clk => clk_gen,

      uart_txd => uart0_txd);

  uart1_checker: entity work.uart_rx

    generic map (uart1_rx_handle)

    port map (

      clk => clk_gen,

      uart_txd => uart1_txd);

  slink_transmitters_gen: for idx in slink_transmitters'range generate

    slink_transmitter : entity vunit_lib.axi_stream_master

      generic map(

        master => slink_transmitters(idx)

      )

      port map(

        aclk => clk_gen,

        tvalid => slink_transmitter_val(idx),

        tready => slink_transmitter_rdy(idx),

        std_ulogic_vector(tdata) => slink_transmitter_dat(idx)

      );

  end generate;

  slink_receivers_gen: for idx in slink_receivers'range generate

  begin

    slink_receiver : entity vunit_lib.axi_stream_slave

      generic map(

        slave => slink_receivers(idx)

      )

      port map(

        aclk => clk_gen,

        tvalid => slink_receiver_val(idx),

        tready => slink_receiver_rdy(idx),

        tdata => std_logic_vector(slink_receiver_dat(idx))

      );

  end generate;

  -- TODO: connect these to the CPU SLINK interface once the

  -- loopback SW has been implemented

  temporary_connection : for idx in slink_transmitters'range generate

    slink_receiver_val(idx) <= slink_transmitter_val(idx);

    slink_transmitter_rdy(idx) <= slink_receiver_rdy(idx);

    slink_receiver_dat(idx) <= slink_transmitter_dat(idx);

  end generate;

  -- Wishbone Fabric ------------------------------------------------------------------------

  -- -------------------------------------------------------------------------------------------

  -- CPU broadcast signals --

  wb_mem_a.addr  <= wb_cpu.addr;

  wb_mem_a.wdata <= wb_cpu.wdata;

  wb_mem_a.we    <= wb_cpu.we;

  wb_mem_a.sel   <= wb_cpu.sel;

  wb_mem_a.tag   <= wb_cpu.tag;

  wb_mem_a.cyc   <= wb_cpu.cyc;

  wb_mem_b.addr  <= wb_cpu.addr;

  wb_mem_b.wdata <= wb_cpu.wdata;

  wb_mem_b.we    <= wb_cpu.we;

  wb_mem_b.sel   <= wb_cpu.sel;

  wb_mem_b.tag   <= wb_cpu.tag;

  wb_mem_b.cyc   <= wb_cpu.cyc;

  wb_mem_c.addr  <= wb_cpu.addr;

  wb_mem_c.wdata <= wb_cpu.wdata;

  wb_mem_c.we    <= wb_cpu.we;

  wb_mem_c.sel   <= wb_cpu.sel;

  wb_mem_c.tag   <= wb_cpu.tag;

  wb_mem_c.cyc   <= wb_cpu.cyc;

  wb_irq.addr    <= wb_cpu.addr;

  wb_irq.wdata   <= wb_cpu.wdata;

  wb_irq.we      <= wb_cpu.we;

  wb_irq.sel     <= wb_cpu.sel;

  wb_irq.tag     <= wb_cpu.tag;

  wb_irq.cyc     <= wb_cpu.cyc;

  -- CPU read-back signals (no mux here since peripherals have "output gates") --

  wb_cpu.rdata <= wb_mem_a.rdata or wb_mem_b.rdata or wb_mem_c.rdata or wb_irq.rdata;

  wb_cpu.ack   <= wb_mem_a.ack   or wb_mem_b.ack   or wb_mem_c.ack   or wb_irq.ack;

  wb_cpu.err   <= wb_mem_a.err   or wb_mem_b.err   or wb_mem_c.err   or wb_irq.err;

  -- peripheral select via STROBE signal --

  wb_mem_a.stb <= wb_cpu.stb when (wb_cpu.addr >= ext_mem_a_base_addr_c) and (wb_cpu.addr < std_ulogic_vector(unsigned(ext_mem_a_base_addr_c) + ext_mem_a_size_c)) else '0';

  wb_mem_b.stb <= wb_cpu.stb when (wb_cpu.addr >= ext_mem_b_base_addr_c) and (wb_cpu.addr < std_ulogic_vector(unsigned(ext_mem_b_base_addr_c) + ext_mem_b_size_c)) else '0';

  wb_mem_c.stb <= wb_cpu.stb when (wb_cpu.addr >= ext_mem_c_base_addr_c) and (wb_cpu.addr < std_ulogic_vector(unsigned(ext_mem_c_base_addr_c) + ext_mem_c_size_c)) else '0';

  wb_irq.stb   <= wb_cpu.stb when (wb_cpu.addr =  irq_trigger_base_addr_c) else '0';

  -- Wishbone Memory A (simulated external IMEM) --------------------------------------------

  -- -------------------------------------------------------------------------------------------

  generate_ext_imem:

  if ext_imem_c generate

    ext_mem_a_access: process(clk_gen)

      variable ext_ram_a : mem32_t(0 to ext_mem_a_size_c/4-1) := mem32_init_f(application_init_image, ext_mem_a_size_c/4); -- initialized, used to simulate external IMEM

    begin

      if rising_edge(clk_gen) then

        -- control --

        ext_mem_a.ack(0) <= wb_mem_a.cyc and wb_mem_a.stb; -- wishbone acknowledge

        -- write access --

        if ((wb_mem_a.cyc and wb_mem_a.stb and wb_mem_a.we) = '1') then -- valid write access

          for i in 0 to 3 loop

            if (wb_mem_a.sel(i) = '1') then

              ext_ram_a(to_integer(unsigned(wb_mem_a.addr(index_size_f(ext_mem_a_size_c/4)+1 downto 2))))(7+i*8 downto 0+i*8) := wb_mem_a.wdata(7+i*8 downto 0+i*8);

            end if;

          end loop; -- i

        end if;

        -- read access --

        ext_mem_a.rdata(0) <= ext_ram_a(to_integer(unsigned(wb_mem_a.addr(index_size_f(ext_mem_a_size_c/4)+1 downto 2)))); -- word aligned

        -- virtual read and ack latency --

        if (ext_mem_a_latency_c > 1) then

          for i in 1 to ext_mem_a_latency_c-1 loop

            ext_mem_a.rdata(i) <= ext_mem_a.rdata(i-1);

            ext_mem_a.ack(i)   <= ext_mem_a.ack(i-1) and wb_mem_a.cyc;

          end loop;

        end if;

        -- bus output register --

        wb_mem_a.err <= '0';

        if (ext_mem_a.ack(ext_mem_a_latency_c-1) = '1') and (wb_mem_b.cyc = '1') and (wb_mem_a.ack = '0') then

          wb_mem_a.rdata <= ext_mem_a.rdata(ext_mem_a_latency_c-1);

          wb_mem_a.ack   <= '1';

        else

          wb_mem_a.rdata <= (others => '0');

          wb_mem_a.ack   <= '0';

        end if;

      end if;

    end process ext_mem_a_access;

  end generate;

  generate_ext_imem_false:

  if (ext_imem_c = false) generate

    wb_mem_a.rdata <= (others => '0');

    wb_mem_a.ack   <= '0';

    wb_mem_a.err   <= '0';

  end generate;

  -- Wishbone Memory B (simulated external DMEM) --------------------------------------------

  -- -------------------------------------------------------------------------------------------

  ext_mem_b_access: process(clk_gen)

    variable ext_ram_b : mem32_t(0 to ext_mem_b_size_c/4-1) := (others => (others => '0')); -- zero, used to simulate external DMEM

  begin

    if rising_edge(clk_gen) then

      -- control --

      ext_mem_b.ack(0) <= wb_mem_b.cyc and wb_mem_b.stb; -- wishbone acknowledge

      -- write access --

      if ((wb_mem_b.cyc and wb_mem_b.stb and wb_mem_b.we) = '1') then -- valid write access

        for i in 0 to 3 loop

          if (wb_mem_b.sel(i) = '1') then

            ext_ram_b(to_integer(unsigned(wb_mem_b.addr(index_size_f(ext_mem_b_size_c/4)+1 downto 2))))(7+i*8 downto 0+i*8) := wb_mem_b.wdata(7+i*8 downto 0+i*8);

          end if;

        end loop; -- i

      end if;

      -- read access --

      ext_mem_b.rdata(0) <= ext_ram_b(to_integer(unsigned(wb_mem_b.addr(index_size_f(ext_mem_b_size_c/4)+1 downto 2)))); -- word aligned

      -- virtual read and ack latency --

      if (ext_mem_b_latency_c > 1) then

        for i in 1 to ext_mem_b_latency_c-1 loop

          ext_mem_b.rdata(i) <= ext_mem_b.rdata(i-1);

          ext_mem_b.ack(i)   <= ext_mem_b.ack(i-1) and wb_mem_b.cyc;

        end loop;

      end if;

      -- bus output register --

      wb_mem_b.err <= '0';

      if (ext_mem_b.ack(ext_mem_b_latency_c-1) = '1') and (wb_mem_b.cyc = '1') and (wb_mem_b.ack = '0') then

        wb_mem_b.rdata <= ext_mem_b.rdata(ext_mem_b_latency_c-1);

        wb_mem_b.ack   <= '1';

      else

        wb_mem_b.rdata <= (others => '0');

        wb_mem_b.ack   <= '0';

      end if;

    end if;

  end process ext_mem_b_access;

  -- Wishbone Memory C (simulated external IO) ----------------------------------------------

  -- -------------------------------------------------------------------------------------------

  ext_mem_c_access: process(clk_gen)

  begin

    if rising_edge(clk_gen) then

      -- control --

      ext_mem_c.ack(0) <= wb_mem_c.cyc and wb_mem_c.stb; -- wishbone acknowledge

      -- write access --

      if ((wb_mem_c.cyc and wb_mem_c.stb and wb_mem_c.we) = '1') then -- valid write access

        for i in 0 to 3 loop

          if (wb_mem_c.sel(i) = '1') then

            ext_ram_c(to_integer(unsigned(wb_mem_c.addr(index_size_f(ext_mem_c_size_c/4)+1 downto 2))))(7+i*8 downto 0+i*8) <= wb_mem_c.wdata(7+i*8 downto 0+i*8);

          end if;

        end loop; -- i

      end if;

      -- read access --

      ext_mem_c.rdata(0) <= ext_ram_c(to_integer(unsigned(wb_mem_c.addr(index_size_f(ext_mem_c_size_c/4)+1 downto 2)))); -- word aligned

      -- virtual read and ack latency --

      if (ext_mem_c_latency_c > 1) then

        for i in 1 to ext_mem_c_latency_c-1 loop

          ext_mem_c.rdata(i) <= ext_mem_c.rdata(i-1);

          ext_mem_c.ack(i)   <= ext_mem_c.ack(i-1) and wb_mem_c.cyc;

        end loop;