abstraction level: discrete events; semantics: queue of future events

specification units:

• entity : interface specification (ports: names, types and directions of I/O signals)
  • may have parameters, by generic declarations
• architecture : specification of the entity internals

more than one architecture may be associated to a given entity, following different specification styles:

• functional : in terms of sequential processes, activated by change of given signals (sensitivity list)
• behavioral : in terms of concurrent assignments (signal relations)
• structural : in terms of components and port connections between instances thereof

encapsulation and hierarchy:

• components: entity-like encapsulation, structural hierarchy
• processes: encapsulate functionality, yet process nesting is not allowed

see Zwolinski ch. 3 for a primer on syntax of VHDL constructs and simple examples

the VHDL translation produced by the Gezel code generator sometimes yields an unexpected outcome...

• create the source file delay_collatz.fdl containing the second version of the Gezel example shown in the second lecture (the file is available in the lab reserved area, in the 3x+1 folder)
• run from the command line: fdlvhd delay_collatz.fdl
• launch Quartus and in this system create a new project named delay_collatz
• copy the .vhd files produced by step 2 into the project directory and open file delay_collatz.vhd in the Quartus editor
• assign the aforementioned files to the project, compile and visualize the resulting error message, then, by double-click on the error message in the compilation report, find out the VHDL source line causing the error
• analyse the delay_collatz.vhd source and find a suitable modification that would fix the error
• set the clock to a frequency that warrants a positive value for the worst-case slack (see clock fine tuning tips from the first lab lab experience)
• compare usage of resources (n. of LEs and registers) and worst-case slack with those obtained from compilation and timing analysis completed in the second lab experience
• create test waveforms for the collatz circuit, with clock input corresponding to the frequency established in the previous step, initial value 27 for the first trajectory and, as a follow-up in the same waveform, another initial value for a second trajectory after 75 clock cycles
• run the functional simulation and check the correspondence of the outcome to expectations
• find out whether and how could one modify the Gezel source delay_collatz.fdl in such a way that its translation to VHDL would not break the compilation

recommended readings:

• Schaumont, Ch. 5, Sect. 5.1-5.2
• Zwolinski, Ch. 3, Sect. 3.1-3-7

other sources for consultation:

• Brandolese, Fornaciari, App. B
• Zwolinski, App. B
• Marwedel, Ch. 2, Sect. 2.7
• Vahid, Digital Design, Ch. 9, Hardware Description Languages (PDF slides)
• Smith, VHDL & Verilog Compared & Contrasted