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Diffstat (limited to 'doc/references/ImplementationOfVITAL.rst')
| -rw-r--r-- | doc/references/ImplementationOfVITAL.rst | 42 |
1 files changed, 21 insertions, 21 deletions
diff --git a/doc/references/ImplementationOfVITAL.rst b/doc/references/ImplementationOfVITAL.rst index 3cf99663c..77e7096c0 100644 --- a/doc/references/ImplementationOfVITAL.rst +++ b/doc/references/ImplementationOfVITAL.rst @@ -10,8 +10,8 @@ Implementation of VITAL .. index:: 1076.4 -This chapter describes how VITAL is implemented in GHDL. Support of VITAL is -really in a preliminary stage. Do not expect too much of it as now. +This chapter describes how VITAL is implemented in GHDL. Support of VITAL is +really in a preliminary stage. Do not expect too much of it as of right now. .. _vital_packages: @@ -21,14 +21,14 @@ VITAL packages The VITAL standard or IEEE 1076.4 was first published in 1995, and revised in 2000. -The version of the VITAL packages depends on the VHDL standard. VITAL +The version of the VITAL packages depends on the VHDL standard. VITAL 1995 packages are used with the VHDL 1987 standard, while VITAL 2000 -packages are used with other standards. This choice is based on the +packages are used with other standards. This choice is based on the requirements of VITAL: VITAL 1995 requires the models follow the VHDL 1987 standard, while VITAL 2000 requires the models follow VHDL 1993. The VITAL 2000 packages were slightly modified so that they conform to -the VHDL 1993 standard (a few functions are made pure and a few one +the VHDL 1993 standard (a few functions are made pure and a few impure). .. _vhdl_restrictions_for_vital: @@ -40,18 +40,18 @@ The VITAL standard (partially) implemented is the IEEE 1076.4 standard published in 1995. This standard defines restriction of the VHDL language usage on VITAL -model. A :dfn:`VITAL model` is a design unit (entity or architecture) +model. A :dfn:`VITAL model` is a design unit (entity or architecture) decorated by the `VITAL_Level0` or `VITAL_Level1` attribute. These attributes are defined in the `ieee.VITAL_Timing` package. -Currently, only VITAL level 0 checks are implemented. VITAL level 1 models +Currently, only VITAL level 0 checks are implemented. VITAL level 1 models can be analyzed, but GHDL doesn't check they comply with the VITAL standard. Moreover, GHDL doesn't check (yet) that timing generics are not read inside a VITAL level 0 model prior the VITAL annotation. -The analysis of a non-conformant VITAL model fails. You can disable the -checks of VITAL restrictions with the *--no-vital-checks*. Even when +The analysis of a non-conformant VITAL model fails. You can disable the +checks of VITAL restrictions with the *--no-vital-checks*. Even when restrictions are not checked, SDF annotation can be performed. .. _backannotation: @@ -64,31 +64,31 @@ Backannotation :dfn:`Backannotation` is the process of setting VITAL generics with timing information provided by an external files. -The external files must be SDF (Standard Delay Format) files. GHDL -supports a tiny subset of SDF version 2.1, other version number can be -used, provided no features added by the next version are used. +The external files must be SDF (Standard Delay Format) files. GHDL +supports a tiny subset of SDF version 2.1. Other version numbers can be +used, provided no features added by later versions are used. Hierarchical instance names are not supported. However you can use a list of -instances. If there is no instance, the top entity will be annotated and -the celltype must be the name of the top entity. If there is at least one +instances. If there is no instance, the top entity will be annotated and +the celltype must be the name of the top entity. If there is at least one instance, the last instance name must be a component instantiation label, and the celltype must be the name of the component declaration instantiated. -Instances being annotated are not required to be VITAL compliant. However +Instances being annotated are not required to be VITAL compliant. However generics being annotated must follow rules of VITAL (e.g., type must be a suitable vital delay type). Currently, only timing constraints applying on a timing generic of type -`VitalDelayType01` has been implemented. This SDF annotator is -just a proof of concept. Features will be added with the following GHDL +`VitalDelayType01` has been implemented. This SDF annotator is +just a proof of concept. Features will be added with the following GHDL release. Negative constraint calculation =============================== -Negative constraint delay adjustment are necessary to handle negative -constraint such as a negative setup time. This step is defined in the VITAL +Negative constraint delay adjustments are necessary to handle negative +constraints such as a negative setup time. This step is defined in the VITAL standard and should occur after backannotation. -GHDL does not do negative constraint calculation. It fails to handle models -with negative constraint. I hope to be able to add this phase soon. +GHDL does not do negative constraint calculation. It fails to handle models +with negative constraint. I hope to be able to add this phase soon. |