Arrays

A Bounded Array Sized in C

Integer arrays fully defined in C can be passed to VHDL by first passing their size, so that an appropriate array type can be created to hold the array’s pointer. After that, a VHDL subprogram can be defined to return the array access.

A Bounded Array Sized in C: First defined in main()

If the integer array must be created or filled by some more advanced process before VHDL can request the array’s pointer, it is possible to execute the GHDL simulation within a custom int main() entrypoint (see basic). In this example the custom entrypoint prompts the user for the size of the array and then handles the variables appropriately before going on to execute the GHDL simulation.

A Bounded Array Sized in VHDL

Interface generics are the generics of the toplevel VHDL entity, and their values can be set via GHDL’s runtime option -g (see Simulation options). In this example an interface generic is used as an argument for the call of the VHPIDIRECT subprogram c_intArr_ptr(arraySize: integer). This subprogram is linked to the foreign C function getIntArr_ptr(int arraySize) which uses the argument to allocate an int* enough space to contain arraySize integers, populating each index thereafter. The subprogram returns the array’s pointer and each index is printed out in VHDL.

Note

The C function is actually extended to handle a second call. If the int* has been used before its memory is freed, and if the new arraySize is greater than 0, the pointer is allocated enough memory again. In this way, a VHDL subprogram call of c_intArr_ptr(0); frees the previously allocated memory.