Altera Nios II C2H Compiler Bedienungsanleitung PDF herunterladen (Seite 55)

Altera Corporation 9.1 3–15

November 2009 Nios II C2H Compiler User Guide

C-to-Hardware Mapping Reference

• Arrays that are initialized

• Global variables

• Static variables

Avalon-MM master ports are generated even when local arrays

(such as the ones discussed here) are referenced. These master

ports only connect to internal slave ports inside the accelerator.

However, the master ports do appear in the C2H Compiler build

report.

Example 3–7 demonstrates the creation of a local 4 kbyte memory inside

the accelerator to store array data[1024]. Because this memory buffer

is large, it translates to an embedded memory block.

Example 3–7. Local Array That Uses 4 KBytes of On-Chip Memory Inside Accelerator

int my_func(int a_parameter)

{

int data[1024]; // 1K 4-byte ints

... // Body of the function

return data[0];

}

Global and Static Variables

Global and static variables must persist outside the scope of the

accelerated function, and they have real addresses accessible by the

processor. For this reason, global and static variables are stored in

memory that the processor can access, outside of the accelerator

hardware. In other words, the C2H Compiler does not affect the location

of these variables; it creates logic in the accelerator capable of accessing

the memory where the variables reside.

References to global and static variables translate to master ports in

hardware, which enable access to a given variable's specific memory

location. For further details, refer to section “Memory Accesses” on

page 3–15.

Memory

Accesses

Hardware accelerators generated by the C2H Compiler use Avalon-MM

master ports to access memory, similar to the Nios II processor and other

SOPC Builder components. The Altera

SOPC Builder system integration

tool handles the task of physically connecting both accelerators and

processors to memory, and creating arbitration logic. As a result, the

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Altera Nios II C2H Compiler Bedienungsanleitung Seite 55