[vhdl-200x-ft] VHDL Fixed-Point Comment

Hi,

 

I am wondering with the VHDL fixed-point package would it benefit anyone if
two new attributes 'ilength and 'flength could be added to the LRM or is
there is a way for the designer to define 'ilength and 'flength in a custom
user defined package. 'ilength would return a natural that would be the
number of integer bits and 'flength also would return a natural that would
be the number of fractional bits. For obtaining the number of integer bits
'ilength would be a constant method for both the sfixed and ufixed types.
Currently to obtain the number of integer bits the 'high returns the correct
number for sfixed but for ufixed a 'high+1 needs to be done to obtain the
correct number.  The 'ilength would clean up the users code by removing
'high+1 or 'high with a common attribute that would return the correct
number based on the data type sfixed or ufixed.  For consistency and to keep
vector lengths positive, the 'flength would return the number of fractional
bits without having to do abs(fp'low).  This could clean up the resulting
code and make it easier to read within a design team.

 

I have started building a fixed-point library to help speed up translation
of the Mathworks Simulink Fixed-Point Models to VHDL and having the ability
to call a 'ilength or 'flength would come in handy on building very generic
synthesizable VHDL fixed-point library(being able to have fully generic
arrays and records (i.e. a vector/matrix of sfixed and/or ufixed and complex
sfixed and a complex ufixed along with vector/matrix of complex sfixed and
ufixed) such that the element dimension can be defined at the same time as
the array dimensions would also be a major improvement to VHDL arrays and
records - I think this capability will be in the next VHDL revision
correct?). For your information I have had major success in converting
Simulink fixed-point models to VHDL using the current preliminary
fixed-point packages.  Pairing the VHDL fixed-point package with the
Mathworks Simulink and Link for ModelSim tool significantly speeds up
conversion time for the tools I use.  I feel once the VHDL fixed-point
package is officially released this will make things interesting for the
companies that are making automatic HDL code generation from high level
tools such as Simulink.

 

Comments about the 'ilength or 'flength?

 

 

Scott D. Hoy

Phone:301.286.2619

NASA GSFC E-mail: scott.d.hoy@gsfc.nasa.gov

Honeywell - TSI E-mail: scott.hoy@honeywell-tsi.com

Honeywell - TSI

NASA Goddard Space Flight Center