Altera Nios II C2H Compiler Manual de usuario descargar pdf (Pagina 66)

3–26 9.1 Altera Corporation

Nios II C2H Compiler User Guide November 2009

Memory Accesses

Example 3–17 connects the variable x in function myfunc to the memory

module named sdram with an arbitration share of 16.

Example 3–17. Pragma Specifying Arbitration Share

#pragma altera_accelerate connect_variable myfunc/x to sdram \

arbitration_share 16

Specifying Flow Control

Avalon-MM transfers with flow control force a master port to obey flow

control signals controlled by a slave port. For example, a slave FIFO might

assert flow control signals to prevent write transfers when the FIFO

memory is full. The C2H Compiler provides a flow control pragma which

enables flow control for all master ports related to a specific pointer

variable.

The flow control pragma is defined as follows:

#pragma altera_accelerate \

enable_flow_control_for_pointer \

The flow control pragma must be placed in the same file as the function

to be accelerated, but outside the function. <function name> and

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

pointer variable.

f For details about Avalon-MM flow control, refer to the Avalon Memory-

Mapped Interface Specification.

Array Subscript Operator

The C2H Compiler converts array subscript operations to equivalent

pointer dereferences, and then translates the pointer dereferences to

hardware. An array is a pointer with abstractions of length and

dimension. The value of an array type is defined to be a pointer to its first

element. The C language specification defines the array subscript

operator as follows:

The definition of the subscript operator [] is that E1[E2] is identical to

(*((E1)+(E2))).

By this definition, any array subscripting (indexing) operation can be

expressed in terms of an indirection (pointer dereference) operation.

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Altera Nios II C2H Compiler Manual de usuario Pagina 66