Altera Nios II C2H Compiler - Manual (Page 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.