Altera Nios II C2H Compiler Uživatelský manuál stáhnout pdf (Strana 119)

Altera Corporation 9.1 6–1

November 2009

6. Pragma Reference

Introduction

The C2H Compiler uses pragmas that allow user control of master-slave

connections and arbitration shares. This chapter describes these pragmas

in detail.

The C language specification dictates that when a compiler

implementation encounters a pragma directive it does not recognize, the

compiler ignores the pragma. By using pragmas, you can write directives

to optimize the C2H Compiler results, without making the C code

incompatible with other compilers.

Connection

Pragma

The C2H Compiler provides a connection pragma that associates a

pointer variable with an Avalon-MM slave port, which is typically a

memory. A pointer variable can translate to one or more master ports,

depending on how many times it is dereferenced in the C code. The

connection pragma directs the C2H Compiler to connect all master ports

generated for a particular variable to a specific slave port in the SOPC

Builder system, reducing arbitration logic.

The connection pragma syntax is as follows:

#pragma altera_accelerate connect_variable \

<function name>/<variable name> to \

<module>[/<slave name>] [arbitration_share <shares>]

<function name> and <variable name> are the exact names of the

accelerated function and the pointer variable. <module> is the exact name

of the component instance, as specified in SOPC Builder. <slave name> is

optional. If provided, <slave name> is the exact name of a specific slave

port on <module>; if not provided, the master port connects to all slave

ports on <module>. <shares> is a positive integer from 1 to 100.

Define the connection pragma in the same file as the function to be

accelerated, outside the function body.

To connect a variable's master ports to multiple slave ports, you can use

multiple pragmas. If you use the connection pragma for a specific

variable, the C2H Compiler connects only the slave ports specified in

pragma statements.

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Altera Nios II C2H Compiler Uživatelský manuál Strana 119