Records
A record in VHDL is a custom data type that allows you to group multiple signals or fields into a single variable. It is similar to a struct in programming languages.
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Purpose:
The main advantage of using records is that when you have a set of related signals—like multiple fields of a register or multiple readings from a sensor—you can organize them into one single signal. This makes your design cleaner and more readable.
Example:
VHDL
Request register contains three fields with different data types and with the help of record this is accessed by a single variable.
Why we need dummy variable in Record
If you are creating a record and at that time there are no functional signals available or you want to reserve fields for future use, then you should add a dummy field.
This ensures that:
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The record is syntactically complete, so the compiler or synthesis tool doesn’t give warnings.
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It’s easy to add real fields later without changing the record structure.
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Bus width or module interface remains consistent.
In short, when you create a record, adding a dummy field is necessary if there is no actual signal yet.
VHDL
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Syntactically complete: The record has at least one dummy field, so VHDL tools don’t complain about an empty record.
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Future expansion: Later, you can replace the dummy field with a real signal or add more fields without changing the existing design. For example:
VHDL
The dummy field acted as a placeholder to keep the record ready for future updates.​