2D Perlin Noise Generator Accelerator

This is simple example that generate 2D perlin noise in FPGA and write the values to a file as python style lists. The main aim of this example is to introduce the DATAFLOW pragma which enable task level parallelism. However, the main purpose of using DATAFLOW pragma is to show how writing HLS C++ code for hardware generally requires a diffrent style of programming.

void perlin(int nx, int ny, float* result, const float freq)
{
#pragma HLS INTERFACE m_axi port=result
#pragma HLS DATAFLOW
    
    hls::stream<Coord> coord_stream;
    hls::stream<float> noise_stream;

    const int N = nx*ny;

    gen_coord(coord_stream, nx, ny, freq);
    perlin_calc(coord_stream, noise_stream, N);
    write_mem(noise_stream, result, N);
}

In the code snippet above, it might seem like gen_coord is executed and then perlin_calc and write_mem respectively. In real hardware, those three functions are actually executed concurrently with data streams (coord_stream and noise_stream) connecting them. The data ‘flows’ between those 3 tasks, thus the name DATAFLOW.

• gen_coord generate x and y coordiate and write them to coord_stream one by one.
• perlin_calc reads coordinates from coord_stream and writes generated noise values to noise_stream.
• write_mem reads noise values from noise_stream and writes them to memory.

For more complex dataflows, the flow must be carefully designed to prevent any potential deadlocks.

Setup

This must be done everytime a new terminal is opened

source /opt/xilinx/xrt/setup.sh
# Replace <Vitis install path> and <vesion>
source <Vitis install path>/Vitis/<version>/settings64.sh
export PLATFORM_REPO_PATHS=/opt/xilinx/platforms
# Change to appropiate platform
export PLATFORM=xilinx_u250_gen3x16_xdma_4_1_202210_1

For software emulation:

export XCL_EMULATION_MODE=sw_emu
cd sw_emu

For hardware emulation:

export XCL_EMULATION_MODE=hw_emu
cd hw_emu

For hardware:

cd hw

Build Host Software

g++ -Wall -g -std=c++11 ../src/host.cpp -o perlin -I${XILINX_XRT}/include/ -L${XILINX_XRT}/lib/ -lOpenCL -pthread -lrt -lstdc++

Build And Link Kenel

# Replace ${TARGET} with / Set TARGET to:
#  sw_emu if targeting software emulation
#  hw_emu if targeting hardware emulation
#  hw if targeting hardware
v++ -c -t ${TARGET} --platform ${PLATFORM} --config ../src/perlin.cfg -k perlin -I../src ../src/perlin.cpp -o perlin.xo
v++ -l -t ${TARGET} --platform ${PLATFORM} --config ../src/perlin.cfg ./perlin.xo -o perlin.xclbin

Configure Emulator

Only when targeting software/hardware emulation

emconfigutil --platform ${PLATFORM} --nd 1

Run the host software

# Replace <W> with width, <H> with height, and <freq> with frequency
./perlin perlin.xclbin <W> <H> <freq>

After running, a text file perlin_hls.txt will be generated and contains lists of generated noise value.