Under each application folder, there are two files that describe the application in Halide.

<AHA_path>/aha/Halide-to-Hardware/apps/hardware_benchmarks/apps/<app>/<app>_generator.cpp

<AHA_path>/aha/Halide-to-Hardware/apps/hardware_benchmarks/apps/<app>/process.cpp

In <app>_generator.cpp, there are several knobs that we can control to determine how the images are streamed. The schedule, mywidth, and myunroll are three arguments that we usually focus on. We can change the arguments either by setting HALIDE_GEN_ARGS (e.g. export HALIDE_GEN_ARGS="mywidth=62 myunroll=2 schedule=3" for gaussian) or setting the arguments in both <app>_generator.cpp and process.cpp. To quickly know the HALIDE_GEN_ARGS that work for dense apps, we could check in /aha/aha/util/regress.py.

In order to change the utilization of a certain application, we can change its unrolling by setting myunroll. This would be useful if we want to exploit the maximum utilization of the CGRA array or use low unrolling duplication to get higher frequency. However, there are certain rules needed to be honored when changing the unrolling.

1. output width % unroll == 0
2. input bank width < 20 || input bank width % 4 == 0

The variables can be calculated as follows:

• The output width is the mywidth set in <app>_generator.cpp and process.cpp.
• input bank width = ceiling(input width / unroll).
• The input width depends on which application you are running. For most dense applications (e.g. gaussian, harris_color, unsharp), input width = output width + filter size - 1. The filter size could be found in <app>_generator.cpp. Take the gaussian for example, filter size = 3.

In most cases, the images are not streamed to the CGRA at one time, but are divided into several tiles first and then streamed tile by tile. When you run the bitstream generation and the rtl simulation test, you only get the estimated frequency, cycle delays, and simulation result for one tile. We can change the tile size by adjusting the tileWidth and tileHeight in <app>_generator.cpp for specific purposes. For example, if we want to accelerate the spin time for CI test, we can set a smaller tile size by reducing mywidth in HALIDE_GEN_ARGS. If we want to make sure that the whole image is processed correctly, we can set the size to the whole image size to test the functionality of an application.