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4.7. Global Variables
Components can use and update C++ global variables. If you access a global variable in your component function, it is implemented as an Avalon® Memory-Mapped (MM) Host interface, like a pointer parameter.
If you access more than one global variable, each global variable uses the same Avalon® MM Host interface, which results in stallable arbitration. If you use pointers and non-constant global memory accesses, then the pointers and global memory accesses all share the same Avalon® MM Host interface.
In addition to the Avalon® MM Host interface, each global variable that the component uses has an input conduit that must be supplied with the address of the global variable in system memory. The input conduit arguments that are generated in the RTL are named @<global variable name> . Input conduits generated for pointer arguments omit the @ are named for the corresponding pointer argument.
If your global variable is declared as const, then no Avalon® MM Host interface and no additional input conduit is generated. Therefore, global variables declared as const use significantly less FPGA area than modifiable global variable.
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