Library of reusable VHDL components
coverage 4.7KB


The original repository is now located on my own git-server at It is mirrored to github with every push, so both should be in sync.


A LGPL3 licensed library of reusable components for VHDL designs and testbenches.

The intention of this library is not to realize the most optimized and highest performing code. Instead it serves more as an example how to implement various things in VHDL and test them efficiently.


(Non-)synthesizable components for testbenches

AssertP (Deprecated, better use Alerts from OSVVM instead)

Package with various assertion procedures.

  • assert_true(x[, str, level]) checks if boolean x = false
  • assert_false(x[, str, level]) checks if boolean x = false
  • assert_equal(x, y[, str, level]) checks if x = y
  • assert_unequal(x, y[, str, level]) checks if x /= y

All of the assert_* procedures have following optional parameters:

  • str print string str to console instead implemented one
  • level severity level (note, warning, error, failure)

Package with various components general useful for simulation

  • wait_cycles(x, n) waits for n rising edges on std_logic signal x
  • spi_master() configurable master for SPI protocol, supports all cpol/cpha modes
  • spi_slave() configurable slave for SPI protocol, supports all cpol/cpha modes

Generic package with various implementations of queue types:

  • t_simple_queue simple array based FIFO queue
  • t_list_queue linked list FIFO queue using access types

Generic package with implementation of dictionary (aka associative array) type:

  • t_dict linked list dictionary using access types


Synthesizable components for implementing in FPGA


Configurable SPI master with support modes 0-3 and simple VAI local backend.


Configurable SPI slave with support modes 0-3 and simple VAI local backend.


Configurable UART transmitter


Configurable UART receiver


Simple WishBone bus master with support of classic single write & read


Simple WishBone bus slave with support of classic single write & read and register backend


Unit tests for each component


Unit tests for components of QueueP package


Unit tests for components of SimP package


Unit tests for SpiMasterE and SpiSlaveE components


Unit test for UartTx and UartRx components


Unit tests for WishBoneMasterE and WishBoneSlaveE components


Formal verification for selected components


Common utilities


Common functions useful for simulation/synthesis

  • and_reduce(x) returns and of all items in x, collapsed to one std_logic/boolean
  • or_reduce(x) returns or of all items in x, collapsed to one std_logic/boolean
  • xor_reduce(x) returns xor of items in x, collapsed to one std_logic
  • even_parity(x) returns even parity of x
  • odd_parity(x) returns odd parity of x
  • count_ones(x) returns number of ‘1’ in x
  • one_hot(x) returns true if x is one-hot coded, false otherwise
  • is_unknown(x) returns true if x contains ‘U’ bit, false otherwise
  • uint_to_slv(x, l) returns std_logic_vector (unsigned) with length l converted from x (natural)
  • slv_to_uint(x) returns natural converted from x (std_logic_vector) (unsigned)
  • uint_bitsize(x) returns number of bits needed for given x (natural)


To run the tests, you have to install GHDL. You can get it from Your GHDL version should not be too old, because libvhdl needs VHDL-2008 support. So, it’s best to get the latest stable release or build from latest sources.

libvhdl uses the OSVVM library to generate random data for the unit tests. It is shipped with libvhdl as git submodule. You have to use the --recursive option when clone the libvhdl Repository to get it: git clone --recursive

Another useful tool is GTKWave, install it if you want to use the waveform files generated by some of the tests.


Type make to do all tests. You should see the successfully running tests like this:

$ make
ghdl -a --std=02 ../sim/QueueP.vhd QueueT.vhd
ghdl -e --std=02 QueueT
ghdl -r --std=02 QueueT
QueueT.vhd:52:5:@0ms:(report note): INFO: t_simple_queue test finished successfully
QueueT.vhd:87:5:@0ms:(report note): INFO: t_list_queue test finished successfully