Data Access Pattern

The syntax for this pragma is:

#pragma SDS data access_pattern(ArrayName:pattern)

This pragma must be specified immediately preceding a function declaration, or immediately preceding another #pragma SDS bound to the function declaration.

Some notes about the syntax:

pattern can be either SEQUENTIAL or RANDOM, by default it is RANDOM

This pragma specifies the data access pattern in the hardware function. If a copy pragma has been specified for an array argument, SDSoC checks the value of this pragma to determine the hardware interface to synthesize. If the access pattern is SEQUENTIAL, a streaming interface (such as ap_fifo) will be generated. Otherwise, with RANDOM access pattern, a RAM interface will be generated. Refer to Data Motion Network Generation in SDSoC for the usage of this pragma in data motion network generation in SDSoC.

Example 1:

The following code snippet shows an example of using this pragma for an array argument:

#pragma SDS data access_pattern(A:SEQUENTIAL)
void foo(int A[1024], int B[1024])

In the example shown above, a streaming interface will be generated for argument A, while a RAM interface will be generated for argument B. The access pattern for argument A must be A[0], A[1], A[2], ... , A[1023], and all elements must be accessed only once. On the other hand, argument B can be accessed in a random fasion, and each element can be accessed zero or more times.

Example 2:

The following code snippet shows an example of using this pragma for a pointer argument:

#pragma SDS data access_pattern(A:SEQUENTIAL)
void foo(int *A, int B[1024])

In the above example, if argument A is intended to be a streaming port, the two pragmas shown must be applied. Without these, SDSoC synthesizes argument A as a register (IN, OUT, or INOUT based on the usage of A in function foo).

Example 3:

The following code snippet shows the effect of zero_copy pragma (refer to Data Transfer Size) on the access_pattern pragma:

#pragma SDS data zero_copy(A)
#pragma SDS data access_pattern(A:SEQUENTIAL)
void foo(int A[1024], int B[1024])

In the above example, the access_pattern pragama is ignored. Once a zero_copy pragma has been applied to an argument, the AXI4 interface will be synthesized for that argument. Please refer to Zero Copy Data Mover for more details.