ML-TN-001 - AI at the edge: comparison of different embedded platforms - Part 1

Info Box Applies to Machine Learning

Work in progress

History

Version	Date	Notes
1.0.0	September 2020	First public release

Introduction

Thanks to the unstoppable technology progress, nowadays Artificial Intelligence (AI) and specifically Machine Learning (ML) are spreading on low-power, resource-constrained devices as well. In a typical Industrial IoT scenario, this means that edge devices can implement complex inference algorithms that were used to run on the cloud platforms only.

This Technical Note (TN for short) is the first one of a series illustrating how machine learning-based test applications are deployed and perform across different embedded platforms, which are eligible for building such intelligent edge devices.

The idea is to develop one or more reference applications with the help of well-known frameworks/libraries and to test them on these platforms for comparing performances, resource utilization, development flow, etc.

In the following sections, these applications are described in more detail. Each article of this series explores in detail one specific platform or use case.

Reference application #1: fruit classifier

This application implements a classifier like the one described here. There is one notable difference, however, with respect to the linked article. In this case, the model was created from scratch.

Model creation

The model was created and trained using Keras, a high-level API of TensorFlow.

The following block shows its architecture:

Model: "sequential"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
conv2d (Conv2D)              (None, 222, 222, 32)      896       
_________________________________________________________________
activation (Activation)      (None, 222, 222, 32)      0         
_________________________________________________________________
max_pooling2d (MaxPooling2D) (None, 111, 111, 32)      0         
_________________________________________________________________
conv2d_1 (Conv2D)            (None, 109, 109, 32)      9248      
_________________________________________________________________
activation_1 (Activation)    (None, 109, 109, 32)      0         
_________________________________________________________________
max_pooling2d_1 (MaxPooling2 (None, 54, 54, 32)        0         
_________________________________________________________________
conv2d_2 (Conv2D)            (None, 52, 52, 64)        18496     
_________________________________________________________________
activation_2 (Activation)    (None, 52, 52, 64)        0         
_________________________________________________________________
max_pooling2d_2 (MaxPooling2 (None, 26, 26, 64)        0         
_________________________________________________________________
conv2d_3 (Conv2D)            (None, 24, 24, 128)       73856     
_________________________________________________________________
activation_3 (Activation)    (None, 24, 24, 128)       0         
_________________________________________________________________
max_pooling2d_3 (MaxPooling2 (None, 12, 12, 128)       0         
_________________________________________________________________
flatten (Flatten)            (None, 18432)             0         
_________________________________________________________________
dense (Dense)                (None, 256)               4718848   
_________________________________________________________________
activation_4 (Activation)    (None, 256)               0         
_________________________________________________________________
dropout (Dropout)            (None, 256)               0         
_________________________________________________________________
dense_1 (Dense)              (None, 6)                 1542      
_________________________________________________________________
activation_5 (Activation)    (None, 6)                 0         
=================================================================
Total params: 4,822,886
Trainable params: 4,822,886
Non-trainable params: 0

The training was done in the cloud using an AWS EC2 server set up ad hoc.

The dataset was created collecting 240 images of 6 different fruits. 75% of the images were used for the training (training dataset) and the rest was used for test/validation purposes (test dataset, validation dataset). Training the model with a greater number of images would have led to better accuracy, but it wouldn't have changed the inference time.

Several measures were taken to counter the high overfitting tendency due to the small number of images. For instance, new images were synthesized from the existing ones to simulate a larger dataset (data augmentation), as shown below:

New images synthesized from an existing one. Original image by tookapic from Pixabay.com

The following plots show the training history:

Variation of the loss (blue) and the validation loss (orange) through the epochs during training

Variation of the accuracy (blue) and the validation accuracy (orange) through the epochs during training

Articles in this series

The other articles in this series are:

• Part 2: testing application #1 on Mito8M SoM (NXP i.MX8M)
• Part 3: testing application #1 on Xilinx Zynq UltraScale+ MPSoC ZCU104 Evaluation Kit
• Part 4: testing application #1 on NXP i.MX8M Plus EVK