General Information

The en_cl_fix library allows implementing the same algorithms and calculations in different languages (currently VHDL and MATLAB) easily. The main idea behind this is to evaluate the behavior or an algorithm in a high-level language such as MATLAB while implementing it later in VHDL. Thanks to the bit-true models, the correctness of the VHDL implementation can be checked easily by comparing outputs of both implementations

License

This library is published under PSI HDL Library License, which is LGPL plus some additional exceptions to clarify the LGPL terms in the context of firmware development.

Maintainers

Martin Heimlicher [[email protected]]

Changelog

See Changelog

Detailed Documentation

See VHDL Documentation

Tagging Policy

Stable releases are tagged in the form major.minor.bugfix.

• Whenever a change is not fully backward compatible, the major version number is incremented
• Whenever new features are added, the minor version number is incremented
• If only bugs are fixed (i.e. no functional changes are applied), the bugfix version is incremented

Dependencies

The python implementation depends on the numpy package

Simulations and Testbenches

• Python Models
  • Navigate to python/unittest
  • Run python3 en_cl_fix_pkg_test.py
• VHDL Models
  • Start Mmodelsim
  • In the TCL console, navigate to sim
  • run source ./sim.tcl
  • The script automatically prints whether all tests were successful
• MATLAB
  • Currently there are not tests for the MATLAB implementation

Fixed Point Number Format

Format

The fixed point number format used in this library is defined as follows:

[s, i, f]

s: true = Signed number (two's complement), false = Unsigned number i: Number of integer bits f: Number of fractional bits

The total number of bits required is s+i+f.

The value of each bit depending on its position relative to the binary point (i-bits left, f-bits right) is given below.

... [4][2][1].[0.5][0.25][0.125] ...

Some examples are given below:

Number Format	Range	Bit Pattern	Example Int	Example Bits
[true,2,1]	-4 ... +3.5	sii.f	-2.5	101.1
[true,2,2]	-4 ... +3.75	sii.ff	-2.5	101.10
[false,4,0]	0 ... 15	iiii.	5	0101.
[false,4,2]	0 ... 15.75	iiii.ff	5.25	0101.01
[true,4,-2]	-16 ... 12	sii--.	-8	110--.
[true,-2,4]	-0.25 ... +0.1875	s.--ff	0.125	0.--10

Rounding

Several rounding modes are implemented. They are described below

Value	Description	Examples rounded to (true,2,0)
		2.2	2.7	-1.5	-0.5	0.5	1.5
Trunc_s	Cut off bits without any rounding	2	2	-2	-1	0	1
NonSymPos_s	Non-symmetric rounding to positive	2	3	-1	0	1	2
NonSymNeg_s	Non-symmetric rounding to negative	2	3	-2	-1	0	1
SymInf_s	Symmetric rounding to infinity	2	3	-2	-1	1	2
SymZero_s	Symmetric rounding to zero	2	3	-1	0	0	1
ConvEven_s	Convergent rounding to even numbers	2	3	-2	0	0	2
ConvOdd_s	Convertent rounding to odd numbers	2	3	-1	-1	1	1

NonSymPos_s is the most common rounding mode and often aliased as Round_s for simplicity and readability.

NOTE: Use Trunc_s wherever possible for lowest resource usage. If rounding is required, prefer NonSymPos_s for low resource usage.

Documentation

Documentation for each implementation is written in an appropriate way for the corresponding languages.

• VHDL - Doxygen
  • To re-generate the documentation, install doxygen, open the doxygen project doc/doxy_vhdl.doxy and run doxygen.
• MATLAB - Documentation Comments
  • The comments are displayed by matlab automatically when typing help
  • Prerequisite is to add the path to the .m files to the MATLAB path