Tuesday, August 28, 2018

Deep Learning with Raspberry Pi -- Real-time object detection with YOLO v3 Tiny! [updated on Dec 19 2018, detailed instruction included]

A quick note on Dec 18 2018:
Since I posted this article late Aug, I have been inquired many times on the detailed instruction and also the python wrapper. Having been really busy in the last several months, I finally found some spare time completing this blog with detailed instruction! All the information can be found in my GitHub repos which was forked from shizukachan/darknet-nnpack. I have modified the Makefile, added the two Python nonblocking wrapper, and made some other minor modification. It should "almost" work out of the box!

Here goes the updated article

I am a big fan of Yolo (You Only Look Once, Yolo website). Redmon & Farhadi's famous Yolo series work had big impacts on the deep learning society. BTW, their recent "paper" (Yolo v3: an incremental Improvement) is an interesting read as well.

So, what is Yolo? Yolo is a cutting-edge object detection algorithm, i.e., it detects objects from images. Traditionally people used moving windows to scan an image, and then try to recognize each snapshot in every possible window locations. This method is of course very time consuming because there are many different ways to place the window, and many computations need to be done repeatedly. Yolo, standing for "You Only Look Once" (not You Only Live Once), smartly avoids those heavy computations by directly predicting object category and their bounding boxes simultaneously.

YoloV3 is one of the latest updates of Yolo algorithm. The biggest change is that YoloV3 now uses only convolutional layers and no more fully-connected layer. Don't let the technical term scare you away! What does this implies is that YoloV3 does not care about the input image size anymore! As long as the height and width are integer times 32 (such as 224x224, 288x288, 608x288, etc), YoloV3 will work fine! Another major improvement of YoloV3 is that it gives predictions in the intermediate layers as well. Again, what does it mean, is that Yolo3 now does a better job predicting small objects than its previous version!

I will have to skip the technical detail here because the paper explained everything. The only thing you need to know is that Yolo is lightweight and fast and decently accurate. It is so lightweight and fast that it can even be used on Raspberry Pi, a single-board computer with smart-phone-grade CPU and limited RAM and no CUDA GPU, to run object detection in real-time! And, it is also convenient because the authors had provided configuration files and weights trained on COCO dataset. So no need to train your own model if you are only interested to detect common objects.

Although Yolo is super efficient, it still requires quite a lot of computation. The original YoloV3, which was written with a C++ library called Darknet by the same authors, will report "segmentation fault" on Raspberry Pi v3 model B+ because Raspberry Pi simply cannot provide enough memory to load the weight. YoloV3-tiny version, however, can be run on RPI 3, very slowly.

Again, I wasn't able to run YoloV3 full version on Pi 3. I think it wouldn't be possible to do so considering the large memory requirement by YoloV3. This article is all about implementing YoloV3-Tiny on Raspberry Pi Model 3B!

Quite a few steps still have to be done to speed up yolov3-tiny on the pi:
1. Install NNPACK, an acceleration library for the neural network to run on multi-core CPU
2. Add some special configuration to the Makefile to compile the Darknet Yolo source code on Cortex CPU and NNPACK optimization
3. Either install opencv C++ (big pain on raspberry pi) or write some python code to wrap darknet. I believe Yolo comes with a python wrapper but I haven't had a chance to test it on RPI.
4. Download Yolov3-tiny.cfg and Yolov3-tiny.weights. Run Darknet with Yolo tiny version (not full version)!

Sounds complicated? Luckily digitalbrain79 (not me) had already figured it out (https://github.com/digitalbrain79/darknet-nnpack). I had more luck with Shizukachan's fork version. I even made a few more changes to make it easier to follow:

Step 0: prepare Python and Pi Camera

Log in to Raspberry Pi using SSH or directly in terminal.
Make sure pip-install is included (it should come together with Debian
sudo apt-get install python-pip
Install OpenCV. The simplest way on RPI is as follows (do not build from source!):
sudo apt-get install python-opencv
Enable pi camera
sudo raspi-config
Go to Interfacing Options, and enable P1/Camera
You will have to reboot the pi to be able to use the camera
A few additional words here. In the advanced option of raspi-config, you can adjust the memory split between CPU and GPU. Although we would like to allocate more ram to CPU so that the pi can load a larger model, you will want to allocate at least 64MB to GPU as the camera module would require it.

Step 1: Install NNPACK

NNPACK was used to optimize Darknet without using a GPU. It is useful for embedded devices using ARM CPUs.
Idein's qmkl is also used to accelerate the SGEMM using the GPU. This is slower than NNPACK on NEON-capable devices and primarily useful for ARM CPUs without NEON.
The NNPACK implementation in Darknet was improved to use transform-based convolution computation, allowing for 40%+ faster inference performance on non-initial frames. This is most useful for repeated inferences, ie. video, or if Darknet is left open to continue processing input instead of allowed to terminate after processing input.

Install Ninja (building tool)

Install PeachPy and confu
sudo pip install --upgrade git+https://github.com/Maratyszcza/PeachPy
sudo pip install --upgrade git+https://github.com/Maratyszcza/confu
Install Ninja
git clone https://github.com/ninja-build/ninja.git
cd ninja
git checkout release
./configure.py --bootstrap
Install clang (I'm not sure why we need this, NNPACK doesn't use it unless you specifically target it).
sudo apt-get install clang

Install NNPACK

Install modified NNPACK
git clone https://github.com/shizukachan/NNPACK
confu setup
python ./configure.py --backend auto
If you are compiling for the Pi Zero, change the last line to python ./configure.py --backend scalar
You can skip the following several lines from the original darknet-nnpack repos. I found them not very necessary (or maybe I missed something)
It's also recommended to examine and edit https://github.com/digitalbrain79/NNPACK-darknet/blob/master/src/init.c#L215 to match your CPU architecture if you're on ARM, as the cache size detection code only works on x86.
Since none of the ARM CPUs have a L3, it's recommended to set L3 = L2 and set inclusive=false. This should lead to the L2 size being set equal to the L3 size.
Ironically, after some trial and error, I've found that setting L3 to an arbitrary 2MB seems to work pretty well.
Build NNPACK with ninja (this might take * quie * a while, be patient. In fact my Pi crashed in the first time. Just reboot and run again):
do a ls and you should be able to find the folders lib and include if all went well:
Test if NNPACK is working:
In my case, the test actually failed in the first time. But I just ran the test again and all items are passed. So if your test failed, don't panic, try one more time.
Copy the libraries and header files to the system environment:
sudo cp -a lib/* /usr/lib/
sudo cp include/nnpack.h /usr/include/
sudo cp deps/pthreadpool/include/pthreadpool.h /usr/include/
If the convolution-inference-smoketest fails, you've probably hit a compiler bug and will have to change to Clang or an older version of GCC.
You can skip the qmkl/qasm/qbin2hex steps if you aren't targeting the QPU.
Install qmkl
sudo apt-get install cmake
git clone https://github.com/Idein/qmkl.git
cd qmkl
cmake .
sudo make install
Install qasm2
sudo apt-get install flex
git clone https://github.com/Terminus-IMRC/qpu-assembler2
cd qpu-assembler2
makesudo make install
Install qbin2hex
git clone https://github.com/Terminus-IMRC/qpu-bin-to-hex
cd qpu-bin-to-hex
sudo make install

Step 2. Install darknet-nnpack

We have finally finished configuring everything needed. Now simply clone this repository. Note that we are cloning the yolov3branch. It comes with the python wrapper I wrote, correct makefile, and yolov3 weight:
git clone -b yolov3 https://github.com/zxzhaixiang/darknet-nnpack
cd darknet-nnpack
git checkout yolov3
At this point, you can build darknet-nnpack using make. Be sure to edit the Makefile before compiling.

Step 3. Test with YoloV3-tiny

Despite doing so many pre-configurations, Raspberry Pi is not powerful enough to run the full YoloV3 version. The YoloV3-tiny version, however, can be run at about 1 frame per second rate
I wrote two python nonblocking wrappers to run Yolo, rpi_video.py and rpi_record.py. What these two python codes do is to take pictures with PiCamera python library, and spawn darknet executable to conduct detection tasks to the picture, and then save to prediction.png, and the python code will load prediction.png and display it on the screen via opencv. Therefore, all the detection jobs are done by darknet, and python simply provides in and out. rpi_video.py will only display the real-time object detection result on the screen as an animation (about 1 frame every 1-1.5 second); rpi_record.py will also save each frame for your own record (like making a git animation afterwards)
To test it, simply run
sudo python rpi_video.py
sudo python rpi_record.py
You can adjust the task type (detection/classification?), weight, configure file, and threshold in line
yolo_proc = Popen(["./darknet",
                   "-thresh", "0.1"],
                   stdin = PIPE, stdout = PIPE)
For more details/weights/configuration/different ways to call darknet, refer to the official YOLO homepage.
As I mentioned, YoloV3-tiny does not care about the size of the input image. So feel free to adjust the camera resolution as long as both height and width are integer multiplication of 32.

#camera.resolution = (224, 224)
#camera.resolution = (608, 608)
camera.resolution = (544, 416)

Here are my test results:

1. It worked. Yolov3-tiny on Raspberry Pi 3 Model B+ has a frame rate of 1 frame per sec (FPS). The rpi_video.py will print the time it requires Yolov3-tiny to predict on an image. I was able to get numbers like 0.9 second to 1.1 second per frame. Not bad at all! Of course, you can't do any rigorous fast object tracing. But for a surveillance camera, or slow robot, or even drone, 1FPS is promising. NNPACK is critical here. As pointed out by Shizukachan, without NNPACK the frame rate will be lower than 0.1FPS!

2.Make sure the power supply you are using can truly provide 2.4A (which is desired by RPI 3B). I have seen cases that the detection speed drops to 1 frame per 1.7 seconds because the power supply did not provide sufficient power.

3. It worked limitedly. Yolov3-tiny is not that accurate compared to Yolov3 full version. But if you want to detect specific objects in some specific scene, you can probably train your own Yolo v3 model (must be the tiny version) on GPU desktop, and transplant it to RPI. Never try to train the model on RPI. Don't even think about it.. With pre-trained Yolov3-tiny on COCO dataset, some good transfer learning can be leveraged to speed up the training speed.

4. I didn't modify the source code of Yolo. When performing a detection task, Yolo outputs an image with bounding box, label and confidence overlaied on top. If you would like to get such information in a digital form, you will have to dig into Yolo's source code and modify the output part. It should be relatively straightforward.

Finally, the results. Note that I accelerated the video 5 times. The actual frame rate is about 1 frame per second.

Yolov3-tiny successfully detected keyboard, banana, person (me), cup, sometimes sofa, car, etc. It thought curious George as teddy bear all the time, probably because COCO dataset does not have a category called "Curious George stuffed animal". It got confused on the old-fashion calculator and sometimes recognized it as a laptop or a cell phone. But in general, I was very surprised to see the results, and the frame rate! 


  1. Hello Doctor again me :) You helped me more thank you so much! Now, I am trying to implement my distance equation inside the yolo code. Can you help me about? Thank you!

    1. hey. has been super busy recently. any luck on the distance calculation?

  2. hello, thanks for the beautiful post, I worked very well then suddenly the camera has stopped working, you can use a webCam usb? if possible what should I change in the "rpi_video.py"?

    1. you can use a USB camera. but you will have to modify the rpi_video.py file as it was written to get image from PiCam. In the past I didn't get too much luck with a USB camera. It was too slow compared to a Pi Cam

    2. Hi, thanks for your post. You can send me rpi_video.py file modified to work with usb camera? My USB camera is a Logitech C170.

      Best regards

  3. Hi,
    thx for your post. Unfortunately it doesn't work for me. I'm using RasPi 3+ fresh Raspbian Stretch image and following strictly to your instructions. The ninja step throws: "warning: A compatible version of re2c (>= 0.11.3) was not found. changes to src/*.in.cc will not affect your build."

    And going further to NNPACK it stops always at the step "[53/140] CXX test/convolution-output/overfeat-fast.cc" (waited many hours in one run)

    Do you have any ideas how I could solve this issue or do some sort of workaround?

    best wishes

    1. The ninja step throws: "warning: A compatible version of re2c (>= 0.11.3) was not found. changes to src/*.in.cc will not affect your build."

      ==>>sudo apt-get install re2c

  4. hey man it is me again

    check the last comment of here, might interest you and everyone else


    i dont have time to try it tho

    ALSO , there is an optimized version of Opencv for ARM which you can install like this


    1. Thanks for sharing! Also OpenCV4 comes with obj detection. Haven't tried on RPI yet. big pain to build and optimize Opencv on RPI

  5. I have tried different times to install yoloV3 tiny following your instructions, but after a while Raspepberry3 freezes with the
    command: $NINJA_PATH/ninja.

    1. Don't give up. You should see the number of files reducing after each crash. Keep running it, the last few files install a lot quicker. Just reboot after every crash and re-run the command.

  6. Hi, thanks for such a great post. I followed your direction and it works well until I run the test script, where yolo_proc.stdout.read() output none. Any idea why? I ran the one single test on the capture image and it works

    1. I faced the same issue. And I suppose you ran the command in Python3 instead of python2.7. Iff that's the case, then it's the problem of the installation of 'confu' module. Unfortunately for some reason(my guess is due to the fact that python2.7 is going to be obsolete in 2020), it installs by default in Python3. To specify the pip installation only to python2.7, use the command as 'sudo python2 -m pip install --upgrade git+https://github.com/Maratyszcza/confu'. After that, go to the 'ninja' dir and run 'export NINJA_PATH=$PWD' again. Next, which is where the root problem is, go to the 'NNPACK' dir and run 'python ./configure.py --backend auto' as is, again. Now, you execute the 'sudo python rpi_video.py' as is and it should work. I think is should be sufficient for it to work, if not, run the rest of the commands once again.

  7. Sir! Thanks for the great tutorial. I want to access IP camera with this yolo version. Is it necessary to install opencv for that purpose?
    Secondly Are there any data sets available for single objects? Like I just need person detection so I'm looking for a person detection pre-trained model.
    Thanks again!

    1. you will have to modify the way how RPI gets images. Instead of getting it through an onboard PiCam (which you need an opencv), you have to find a way to get frames from the IP camera. You might not need opencv dependent on how you fetch the frames

  8. Hello, sir,
    Thank you for this amazing tutorial.
    But I have a little problem when running with my own model that I have train before on my laptop. I have an error like this
    *** `./darknet 'error: corrupted vs. size. prev_size: 0x00334c10 ***

    can you help me with errors like this? thank you once again

    1. seems to be an issue of darknet. i haven't seen it before. Have you looked this? https://github.com/pjreddie/darknet/issues/105

  9. Everything looks fantastic.Amazing i m really impress with your content and very useful it.hydroglobalreview

  10. This comment has been removed by the author.

  11. Sir,
    I got error at the end
    When I try to run
    sudo python rpi_video.py

    Gtk-WARNING **: cannot open display: :1.0

    Can you help me

    1. Did you connect through SSH+VNC? or you were running directly on rpi?

    2. I get the same problem. I connect it through SSH+VNC.

  12. On step Install NNPACK, I got the error,

    Traceback (most recent call last):
    File "./configure.py", line 4, in
    import confu
    ImportError: No module named confu

    and when I ran, $NINJA_PATH/ninja

    I got

    ninja: no work to do.

    1. did you run "sudo pip install --upgrade git+https://github.com/Maratyszcza/confu" and did it run successfully?

    2. An unknown user posted a possible solution:
      "I faced the same issue. And I suppose you ran the command in Python3 instead of python2.7. Iff that's the case, then it's the problem of the installation of 'confu' module. Unfortunately for some reason(my guess is due to the fact that python2.7 is going to be obsolete in 2020), it installs by default in Python3. To specify the pip installation only to python2.7, use the command as 'sudo python2 -m pip install --upgrade git+https://github.com/Maratyszcza/confu'. After that, go to the 'ninja' dir and run 'export NINJA_PATH=$PWD' again. Next, which is where the root problem is, go to the 'NNPACK' dir and run 'python ./configure.py --backend auto' as is, again. Now, you execute the 'sudo python rpi_video.py' as is and it should work. I think is should be sufficient for it to work, if not, run the rest of the commands once again."

    3. Hi I followed the steps you mention above, but regardless of whether im on python 2 or 3 I keep getting the issue: "Traceback (most recent call last):
      File "./configure.py", line 5, in
      parser = confu.standard_parser()
      AttributeError: module 'confu' has no attribute 'standard_parser'" I dont know what to do anymore I've checked this issue https://github.com/Maratyszcza/confu/issues/4 , tis one: https://github.com/digitalbrain79/darknet-nnpack/issues/22 and this comment and nothing works :(

  13. thanks for share the tutorial.

    I already see your detection and that's amaze me.

    I want to ask something.
    how the way we can make the prediction more accurate and faster in detection?

    Thx in advance :)

    1. To make the prediction more accurate: train the neural network with more images, or use larger neural networks (YoloV3 is much more accurate than YoloV3-tiny, the one I am using here)
      To make the run faster: use more powerful devices than raspberry pi, or use a smaller neural network.

      I don't think there is a way to achieve both on raspberry pi without significant hardware improvement or model improvement

  14. Hello sir,

    i am trying to read from video and then detect via your code.
    My code is: but then I get an error message
    ```im = cv2.imread("one.png")
    ima1 = cv2.cvtColor(im,cv2.COLOR_BGR2RGB)

    Cannot load image " && ;;4EE>PPI^^Wzzs��������������������������~��|��|~~w}} e^^WNNG((!((!&& && $$ "" " " # # " ! !

    STB Reason: can't fopen```

    1. this line -> "yolo_proc.stdin.write(ima1.tostring())"

      you are trying to convert a binary array to string and write to the yolo process. However, what the yolo process is expecting is the filename of the image. so you should only pass 'one.png' to yolo_proc.stdin.write('one.png')

  15. So im trying to write a single image to the stdin

    The ```
    doesnt work neither as the code is expecting a byte array and not a string :/

    1. it is because the code was written in Python 2.7. Bytestring is a Python 3 thing. You can try to add a letter b in front of the string to force it to be a byte string:

    2. Same problem. It freezes with no error when call select.select([yolo_proc.stdout],[],[])

  16. This is enough for installing ninja:
    sudo apt install ninja-build

  17. Hey this is awesome! I saw your post on Rasberry Pi forum and you mentioned this being possible on autonomous vehicles like drones. I'm working on a drone and would like to use a rasberry pi and PiCamera. Would you be able to give me any tips/advice? Anything helps thanks!

  18. Hi bro thanks for this awesome tutorial i got it to work on my rpi! Anyway, do you have any post that teaches how to train my own model or any reference that will serve as a guide? Your reply would be much appreciated!

    1. thanks. glad it worked on your Pi! To train your own model, you have to follow the instruction given in https://pjreddie.com/darknet/yolo/.
      Essentially you have to prepare your input images, labels and boxes. You have to train the model on a desktop or laptop, better with a Nvidia GPU. Then you can copy the trained weight to your Pi

    2. but the trained weights are in terms of .data files instead of .weights and there is no software or procedure to convert the .data (checkpoints) into .weights

  19. File "rpi_record.py", line 35
    copyfile('predictions.png', 'frame%03d.png' % iframe)
    TabError: inconsistent use of tabs and spaces in indentation

    i got this error

    1. I have fixed the indentation. please download the git repos again

  20. Hi Xiang,

    Thank you for the nice artical, it is very helpful!

    I'm wondering if there are some optimizing could be done to this or maybe other CNN frameworks on RPI? Because 1 FPS is still too slow in real usage.

    Thank you again.


  21. hi,

    that is great article, but i got this error

    pi@raspberrypi:~/Downloads/darknet-nnpack $ make
    mkdir -p obj
    mkdir -p results
    gcc -Iinclude/ -Isrc/ -DNNPACK -DNNPACK_FAST -DARM_NEON -Wall -Wno-unknown-pragmas -Wfatal-errors -fPIC -march=native -Ofast -DNNPACK -DNNPACK_FAST -DARM_NEON -mfpu=neon-vfpv4 -funsafe-math-optimizations -ftree-vectorize -c ./src/gemm.c -o obj/gemm.o
    *** Error in `gcc': double free or corruption (top): 0x01e30028 ***
    Makefile:114: recipe for target 'obj/gemm.o' failed
    make: *** [obj/gemm.o] Aborted

    it seems something problem with NNPACK compilation, i got the following error, beside that, that NNPACK test went well

    pi@raspberrypi:~/Downloads/NNPACK $ $NINJA_PATH/ninja
    [11/92] CC src/convolution-inference.c
    /home/pi/Downloads/NNPACK/src/convolution-inference.c: In function 'compute_output_transform':
    /home/pi/Downloads/NNPACK/src/convolution-inference.c:158:59: warning: initialization from incompatible pointer type
    nnp_transform_2d_with_offset transform_function_nobias = context->transform_function;
    /home/pi/Downloads/NNPACK/src/convolution-inference.c: In function 'nnp_convolution_inference':
    /home/pi/Downloads/NNPACK/src/convolution-inference.c:1132:33: warning: assignment from incompatible pointer type
    output_transform_function = nnp_hwinfo.transforms.owt_f6x6_3x3;
    /home/pi/Downloads/NNPACK/src/convolution-inference.c:1167:33: warning: assignment from incompatible pointer type
    output_transform_function = nnp_hwinfo.transforms.ifft8x8_with_offset;
    /home/pi/Downloads/NNPACK/src/convolution-inference.c:1202:33: warning: assignment from incompatible pointer type
    output_transform_function = nnp_hwinfo.transforms.ifft16x16_with_offset;


  22. Hi, may i know can this project works on Raspberry Pi 4?

  23. This comment has been removed by the author.

  24. hello sir, I have a problem when I run the command $ NINJA_PATH / ninja. raspberry 3b + stopped and when I tried again gradually. stopped at [80]

    1. Hello: Did you get a solution to this problem? Thanks

  25. Hey man, thanks alot for the tutorial its been a huge help. Im running it on raspberry Pi 3B+, exactly how you have it set up. The only thing is it takes about 5 seconds for each detection (0.2 FPS), do you have any tips on how i could speed it up?

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  27. That 'ninja' compile that takes quite a while and crashes- likely because the Pi runs out of memory. Use: $NINJA_PATH/ninja -j 2
    to only use 2 cores at once, and it's more likely to complete without crashing.

  28. I found the Pi4 with 4GB of memory can run both the original full Yolo-v3 and the full version of Yolo-v3 with NNPACK as shown here. The NNPACK version is hugely faster (over 10x) however it also gives different results. For example 96% confidence detection on the same input that the original Yolo was 99%.

  29. I also found the NNPACK smoketest failed the first try, but the second try succeeded without changing anything. This leads me to wonder why!?
    [ RUN ] WT8x8_FP16.multi_tile_with_relu
    /home/pi/NNPACK/test/testers/convolution.h:382: Failure
    Expected: (median(maxErrors)) < (errorLimit()), actual: 0.0101598 vs 0.01

  30. Raspberry Pi 4 with gcc 9.2.1, when making darknet I get the error: unrecognized command line option ‘-mfpu=neon-vfpv4’ but it works if I change that to -mtune=cortex-a72

    1. Had this same problem with ubuntu (64bit) on pi 4, the fix worked for me

  31. Great note. How can I modify the code to use a USB-based webcam?

  32. it,s showing like this when i run 'sudo python rpi_video.py '

    (yolov3-tiny:2084): Gtk-WARNING **: 01:42:57.268: cannot open display:

    i am using raspberry pi 4 and i don't have a display connected to pi. i am ssh ing through wifi, and also i need to save the detection output details as a text file.

    please help me. its for my college project

  33. Just wanted to leave a like, was easy to follow, and worked like a charm!

  34. Getting segmentation fault
    Loading weights from yolov3-tiny.weights...
    seen 64, trained: 64 K-images (1 Kilo-batches_64)
    Done! Loaded 24 layers from weights-file
    Segmentation fault
    Can anybody help out ?

  35. Enjoyed reading the article above, really explains everything in detail, the article is very interesting and effective. Thank you and good luck for the upcoming articles Python Programming Course

  36. Hi I'm trying to run it on a rpi4, the make of yolov3branch give me this error:

    gcc -Iinclude/ -Isrc/ -DNNPACK -DNNPACK_FAST -DARM_NEON -Wall -Wno-unknown-pragmas -Wfatal-errors -fPIC -march=native -Ofast -DNNPACK -DNNPACK_FAST -DARM_NEON -mfpu=neon-vfpv4 -funsafe-math-optimizations -ftree-vectorize obj/captcha.o obj/lsd.o obj/super.o obj/art.o obj/tag.o obj/cifar.o obj/go.o obj/rnn.o obj/segmenter.o obj/regressor.o obj/classifier.o obj/coco.o obj/yolo.o obj/detector.o obj/nightmare.o obj/darknet.o libdarknet.a -o darknet -lm -pthread -lnnpack -lpthreadpool libdarknet.a
    /usr/bin/ld: /usr/lib/gcc/arm-linux-gnueabihf/8/../../../libpthreadpool.a(pthreads.c.o): in function `pthreadpool_create':
    /home/pi/NNPACK/deps/pthreadpool/src/pthreads.c:258: undefined reference to `pthreadpool_allocate'
    /usr/bin/ld: /usr/lib/gcc/arm-linux-gnueabihf/8/../../../libpthreadpool.a(pthreads.c.o): in function `pthreadpool_destroy':
    /home/pi/NNPACK/deps/pthreadpool/src/pthreads.c:459: undefined reference to `pthreadpool_deallocate'
    /usr/bin/ld: /home/pi/NNPACK/deps/pthreadpool/src/pthreads.c:459: undefined reference to `pthreadpool_deallocate'
    /usr/bin/ld: darknet: internal symbol `pthreadpool_deallocate' isn't defined
    /usr/bin/ld: final link failed: bad value
    collect2: error: ld returned 1 exit status
    make: *** [Makefile:105: darknet] Error 1

    1. Also I'm not sure about what I need to change in the makefile
      Tried to use -mtune=cortex-a72 in the CFLAGS and I get a different error:

      gcc -Iinclude/ -Isrc/ -DNNPACK -DNNPACK_FAST -DARM_NEON -Wall -Wno-unknown-pragmas -Wfatal-errors -fPIC -march=native -Ofast -DNNPACK -DNNPACK_FAST -DARM_NEON -mtune=cortex-a72 -funsafe-math-optimizations -ftree-vectorize -c ./src/blas.c -o obj/blas.o
      In file included from ./src/blas.c:10:
      ./src/blas.c: In function ‘scal_cpu’:
      /usr/lib/gcc/arm-linux-gnueabihf/8/include/arm_neon.h:6740:1: error: inlining failed in call to always_inline ‘vdupq_n_f32’: target specific option mismatch
      vdupq_n_f32 (float32_t __a)
      compilation terminated due to -Wfatal-errors.
      make: *** [Makefile:114: obj/blas.o] Error 1

    2. Hello. Any solution regarding this issue. your help will be of great assistance. thanks

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