Altera Nios II C2H Compiler - Manual (Page 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 \
<
function name >/< variable name >
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.