Exporting a Library for GCC

To build a shared library, sds++ requires at least one accelerator. The following example provides three entry points into two hardware accelerators: a matrix multiplier and a matrix adder. You can find these files in the samples/libmatrix/build directory.

• mmult_accel.cpp: Accelerator code for the matrix multiplier
• mmult_accel.h: Header file for the matrix multiplier
• madd_accel.cpp: Accelerator code for the matrix adder
• madd_accel.h: Header file for the matrix adder
• matrix.cpp: Code that calls the accelerators and determines the data motion network
• matrix.h: Header file for the library

The matrix.cpp file contains functions that define the accelerator interfaces as well as how the hardware functions communicate with the platform (that is, the data motion networks between platform and accelerators). The function madd calls a single matrix adder accelerator, and the function mmult calls a single matrix multiplier accelerator. Another function mmultadd is implemented using two hardware functions, with the output of the matrix multiplier connected directly to the input of the matrix adder.

/* matrix.cpp */
#include "madd_accel.h"
#include "mmult_accel.h"
    
void madd(float in_A[MSIZE*MSIZE], float in_B[MSIZE*MSIZE], float out_C[MSIZE*MSIZE])                                             
{
  madd_accel(in_A, in_B, out_C);
}
    
void mmult(float in_A[MSIZE*MSIZE], float in_B[MSIZE*MSIZE], float out_C[MSIZE*MSIZE])                                            
{
  mmult_accel(in_A, in_B, out_C);
}
    
void mmultadd(float in_A[MSIZE*MSIZE], float in_B[MSIZE*MSIZE], float in_C[MSIZE*MSIZE], 
float out_D[MSIZE*MSIZE])
{
  float tmp[MSIZE * MSIZE];
    
  mmult_accel(in_A, in_B, tmp);
  madd_accel(tmp, in_C, out_D);
}

The matrix.h file defines the function interfaces to the shared library and is included in the application source code.

/* matrix.h */
#ifndef MATRIX_H_
#define MATRIX_H_
   
#define MSIZE 16
    
void madd(float in_A[MSIZE*MSIZE], float in_B[MSIZE*MSIZE], float out_C[MSIZE*MSIZE]);
  
void mmult(float in_A[MSIZE*MSIZE], float in_B[MSIZE*MSIZE], float out_C[MSIZE*MSIZE]);
    
void mmultadd(float in_A[MSIZE*MSIZE], float in_B[MSIZE*MSIZE], float in_C[MSIZE*MSIZE], 
float out_D[MSIZE*MSIZE]);
    
#endif /* MATRIX_H_ */

In the samples/libmatrix/build/shared folder, the Makefile shows how the project is built by specifying that the functions mmult_accel, madd, and mmult_add must be implemented in programmable logic.

SDSFLAGS = \
    -sds-pf ${PLATFORM} \
    -sds-hw mmult_accel mmult_accel.cpp -sds-end \
    -sds-hw madd_accel madd_accel.cpp -sds-end

Object files are generated with position independent code (PIC), like standard shared libraries, using the GCC standard -fpic option:

sds++ ${SDSFLAGS} -c -fpic –o mmult_accel.o mmult_accel.cpp
    sds++ ${SDSFLAGS} -c -fpic –o madd_accel.o madd_accel.cpp
    sds++ ${SDSFLAGS} -c -fpic –o matrix.o matrix.cpp

Link the objects files by using the using the GCC standard –shared switch:

sds++ ${SDSFLAGS} -shared -o libmatrix.so mmult_accel.o madd_accel.o matrix.o

After building the project, the following files are generated:

• libmatrix.so: Shared library suitable for linking using GCC and for runtime use
• sd_card: Directory containing an SD card image for booting the board

The following is an example of using the library with a GCC compiler. The library is used by including the header file matrix.h and then calling the necessary library functions.

/* main.cpp (pseudocode) */
#include "matrix.h"
        
int main(int argc, char* argv[])
{
  float *A, *B, *C, *D;
  float *J, *K, *L;
  float *X, *Y, *Z;
  ...
  mmultadd(A, B, C, D);
  ...
  mmult(J, K, L);
  ...
  madd(X, Y, Z);
  ...
}

To compile against a library, the compiler needs the header file. The path to the header file is specified using the -I switch. You can find example files in the samples/libmatrix/use directory.

gcc –I <path_to_library>/include –o main.o main.c

To link against the library, the linker needs the library. The path to the library is specified using the -L switch. Also, ask the linker to link against the library using the -l switch.

gcc –I <path_to_library>/lib –o main.elf main.o -lmatrix

For detailed information on using the GCC compiler and linker switches see the GCC documentation.