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 SDSbound to the function declaration.

Some notes about the syntax:

patterncan be eitherSEQUENTIALorRANDOM, by default it isRANDOM

This pragma specifies the data access pattern in the hardware function. If acopypragma 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 isSEQUENTIAL, a streaming interface (such as ap_fifo) will be generated. Otherwise, withRANDOMaccess pattern, a RAM interface will be generated. Refer toData Motion Network Generation in SDSoCfor 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 argumentA, while a RAM interface will be generated for argumentB. The access pattern for argumentAmust be A[0], A[1], A[2], ... , A[1023], and all elements must be accessed only once. On the other hand, argumentBcan 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 argumentAis intended to be a streaming port, the two pragmas shown must be applied. Without these, SDSoC synthesizes argumentAas a register (IN, OUT, or INOUT based on the usage ofAin functionfoo).

Example 3:

The following code snippet shows the effect of zero_copypragma (refer to Data Transfer Size) on the access_patternpragma:

#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, theaccess_patternpragama is ignored. Once azero_copypragma has been applied to an argument, the AXI4 interface will be synthesized for that argument. Please refer toZero Copy Data Moverfor more details.