STT-tensorflow/tensorflow/lite/micro/kernels/arc_mli

EmbARC MLI Library Based Optimizations of TensorFlow Lite Micro Kernels for ARC Platforms.

This folder contains kernel implementations which use optimized embARC MLI Library. It allows acceleration of inference operations which use int8 (asymmetric quantization).

Usage

embARC MLI Library is used by default to speed up execution of some kernels for asymmetrically quantized layers. This means that usual project generation for ARC specific target implies usage of embARC MLI.

For example:

make -f tensorflow/lite/micro/tools/make/Makefile TARGET=arc_emsdp generate_person_detection_int8_make_project

In case MLI implementation can’t be used, kernels in this folder fallback to TFLM reference implementations. For applications which may not benefit from MLI library, projects can be generated without these implementations by adding TAGS=no_arc_mli in the command line, which can reduce overall code size:

make -f tensorflow/lite/micro/tools/make/Makefile TARGET=arc_emsdp TAGS=no_arc_mli generate_person_detection_int8_make_project

For ARC EM SDP board, a pre-compiled MLI library is downloaded and used in the application. For a custom target ARC-based platform, MLI sources are downloaded and compiled during project generation phase. To build library from sources for ARC EM SDP platform, add BUILD_ARC_MLI=true option to make command:

make -f tensorflow/lite/micro/tools/make/Makefile TARGET=arc_emsdp BUILD_ARC_MLI=true generate_person_detection_int8_make_project

If an application exclusively uses accelerated MLI kernel implementations, one can strip out TFLM reference kernel implementations to reduce code size of application. Build application with MLI_ONLY=true option in generated project (after the project was built):

cd tensorflow/lite/micro/tools/make/gen/arc_emsdp_arc/prj/person_detection_int8/make

make app MLI_ONLY=true

if you try this and application execution fails, then most probably MLI can’t be used for some nodes and you need to revert to using TFLM reference kernels.

Limitations

Currently, the MLI Library provides optimized implementation only for int8 (asymmetric) versions of the following kernels: 1. Convolution 2D – Per axis quantization only, dilation_ratio==1 2. Depthwise Convolution 2D – Per axis quantization only, dilation_ratio==1 3. Average Pooling 4. Max Pooling 5. Fully Connected

Currently only /tensorflow/lite/micro/examples/person_detection_experimental is quantized using this specification. Other examples can be executed on ARC-based targets, but will only use reference kernels.

Scratch Buffers and Slicing

The following information applies only for ARC EM SDP and other targets with XY memory. embARC MLI uses specific optimizations which assumes node operands are in XY memory and/or DCCM (Data Closely Coupled Memory). As operands might be quite big and may not fit in available XY memory, special slicing logic is applied which allows kernel calculations to be split into multiple parts. For this reason, internal static buffers are allocated in these X, Y and DCCM memory banks and used to execute sub-calculations.

All this is performed automatically and invisible to the user. Half of the DCCM memory bank and the full XY banks are occupied for MLI specific needs. If the user needs space in XY memory for other tasks, these arrays can be reduced by setting specific sizes. For this, add the following option to build command replacing <size[a|b|c]> with required values:

EXT_CFLAGS=”-DSCRATCH_MEM_Z_SIZE=<size_a> -DSCRATCH_MEM_X_SIZE=<size_b> -DSCRATCH_MEM_Y_SIZE=<size_c>”

For example, to reduce sizes of arrays placed in DCCM and XCCM to 32k and 8k respectively, use next command:

make app EXT_CFLAGS=”-DSCRATCH_MEM_Z_SIZE=32*1024 -DSCRATCH_MEM_X_SIZE=8*1024”

License

TensorFlow's code is covered by the Apache2 License included in the repository, and third party dependencies are covered by their respective licenses, in the third_party folder of this package.