sobel

cFp Sobel Filter

This is the implementation of the common Median Blur Filter (Sobel), on cloudFPGA platform. The Sobel IP is privided by the open source Xilinx ® Vitis™ Vision library, which is a fundamental library aimed at providing a comprehensive FPGA acceleration library for computer vision algorithms.

Repository and environment setup

git clone --recursive [email protected]:cloudFPGA/cFp_Vitis.git
cd cFp_Vitis
source ./env/setenv.sh

Intergration of Vitis Vision Sobel with cloudFPGA

In the following figure it is shown how straightforward is to intergrate a function from Vitis libraries with cloudFPGA project.

Since most of Vitis libraries (in L1) are offered with a AXI stream I/F in dataflow mode, the most obvious approach to connect them to cF is to wrap this I/F with anohter I/F that takes care of carefully feeding (as well as sending the results back) to (from) the Sobel IP from the network. For cFp_Vitis we are using the Themisto Shell already equipeed with a network streaming I/F for the user application. A small FSM takes care of the data casting between network and AXI streams.

Sobel Simulation

The testbench of Sobel is highlighted below:

The testbench is offered in two flavors:

• HLS TB: The testbench of the C++/RTL. This is a typical Vivado HLS testbench but it includes the testing of Sobel IP when this is wrapped in a cF Themisto Shell.
• Host TB: This includes the testing of a a host apllication (C++) that send/receives images over Ethernet (TCP/UDP) with a cF FPGA. This testbench establishes a socket-based connection with an intermediate listener which further calls the previous testbench. So practically, the 2nd tb is a wrapper of the 1st tb, but passing the I/O data over socket streams. For example this is the system command inside Host TB that calls the HLS TB:

This folder contains the mandatory files to proceed withthe 1st option, i.e. HLS TB

Basic files/module for the HLS TB: 3. test_sobel_app.cpp: The typical Vivado HLS testbench of Sobel IP, when this is wrapped in a Themisto Shell. 4. Themisto Shell: The SHELL-ROLE architecture of cF. 5. cFp_Vitis: The project that bridges Vitis libraries with cF.

Sobel image size

The maximum image size, that the Sobel IP is configured, is defined at https://github.com/cloudFPGA/cFp_Vitis/blob/master/ROLE/vision/host/sobel/include/config.h through the FRAME_HEIGHT and FRAME_WIDTH definitions. These definitions have an impact of the FPGA resources. In the following simulations if the image provided has other dimensions, the cv::resize function will be used to adjust the image (scale) to FRAME_HEIGHT x FRAME_WIDTH.

Note: Remember to run make clean every time you change those definitions.

Run simulation

HLS TB

cd ./ROLE/vision/hls/sobel_app
make fcsim -j 4  # to run simulation using your system's gcc (with 4 threads)
make csim   # to run simulation using Vivado's gcc
make cosim  # to run co-simulation using Vivado

Optional steps

cd ./ROLE/vision/hls/sobel_app
make callgraph # to run fcsim and then execute the binary in Valgrind's callgraph tool
make kcachegrind # to run callgrah and then view the output in Kcachegrind tool
make memcheck # to run fcsim and then execute the binary in Valgrind's memcheck tool (to inspect memory leaks)

Sobel Synthesis

Since curretnly the cFDK supports only Vivado(HLS) 2017.4 we are following a 2-steps synthesis procedure. Firstly we synthesize the Themisto SHELL with Vivado (HLS) 2017.4 and then we synthesize the rest of the project (including P&R and bitgen) with Vivado (HLS) > 2019.1.

The Sobel IP

This is only for the HLS of Sobel (e.g. to check synthesizability)

cd cFp_Vitis/ROLE/vision/hls
make sobel # with Vivado HLS >= 2019.1

or

cd cFp_Vitis/ROLE/vision/hls/sobel
make csynth # with Vivado HLS >= 2019.1

or

cd cFp_Vitis/ROLE/vision/hls/sobel
vivado_hls -f run_hls.tcl # with Vivado HLS >= 2019.1

The Themisto SHELL

cd cFp_Vitis/cFDK/SRA/LIB/SHELL/Themisto
make all # with Vivado HLS == 2017.4

The complete cFp_Vitis

cd cFp_Vitis
make monolithic # with Vivado HLS >= 2019.1

More info for the Sobel IP: https://xilinx.github.io/Vitis_Libraries/vision/2020.1/api-reference.html#median-blur-filter

Troubleshooting

• Vivado libstdc++.so.6: version CXXABI_1.3.11 not found (required by /lib64/libtbb.so.2)`
  

  Fix: cp /usr/lib64/libstdc++.so.6 /tools/Xilinx/Vivado/2020.1/lib/lnx64.o/Default/libstdc++.so.6

• /lib64/libtbb.so.2: undefined reference to `__cxa_init_primary_exception@CXXABI_1.3.11'
  /lib64/libtbb.so.2: undefined reference to `std::__exception_ptr::exception_ptr::exception_ptr(void*)@CXXABI_1.3.11'
  

  Fix: csim_design -ldflags "-L/usr/lib/gcc/x86_64-redhat-linux/8/ ${OPENCV_LIB_FLAGS} ${OPENCV_LIB_REF}" -clean -argv "${SimFile}"

/usr/include/features.h:367:12: fatal error: 'sys/cdefs.h' file not found # include <sys/cdefs.h>

Fix: `sudo apt-get install gcc-multilib g++-multilib`

* Inability to compile vitis libraries for some libs.
Add this fix to the Xilinx makefile
Fix: ```LDFLAGS += `pkg-config --libs opencv` `xml2-config --cflags --libs```