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diff --git a/doc/4_References/ImplementationOfVITAL.rst b/doc/4_References/ImplementationOfVITAL.rst deleted file mode 100644 index 4ffb8159b..000000000 --- a/doc/4_References/ImplementationOfVITAL.rst +++ /dev/null @@ -1,94 +0,0 @@ -.. _REF:ImplVITAL: - -**************************** -GHDL implementation of VITAL -**************************** - -.. index:: VITAL - -.. index:: IEEE 1076.4 - -.. 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. - -.. _vital_packages: - -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 -1995 packages are used with the VHDL 1987 standard, while VITAL 2000 -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 -impure). - -.. _vhdl_restrictions_for_vital: - -VHDL restrictions for VITAL -=========================== - -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) -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 -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 -restrictions are not checked, SDF annotation can be performed. - -.. _backannotation: - -Backannotation -============== - -.. index:: SDF - -: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. - -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 -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 -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 -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 -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. |