ARM Community: Software Enablement - ARM Community

In this post, I will explain the various branch and call instructions available in the ARM and Thumb instruction sets, and why the variants exist. Finally, I will provide a JavaScript tool that can help you find a typical branch sequence matching your requirements.

What Does a Branch Do?

A branch, quite simply, is a break in the sequential flow of instructions that the processor is executing. Some other architectures call them jumps, but they're essentially the same thing. The following is a trivial, and hopefully familiar example of a branch:

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In part one of this series, we introduced the video encode requirement and target development environment. In this part, we start by examining benchmarking result of h.264 encode using x264 on a development host rather than the ARM target. This enables us to perform some initial tuning of the encode settings for our target use case of video conferencing.

1 Benchmarking
For video conferencing, we want low bit rate, but at the same time we must maintain at least a 15 fps frame rate so that video quality is acceptable. So we focus on balancing bit rate, frame rate and video quality when investigating the performance of x264 encoder. In x264, there are many options for enabling and tuning the performance of the encoder. So we test the various combinations and evaluate resultant bit rate and video quality. Since relative bit rate and video quality are facets of the encode algorithm and independent of the hardware platform, we first test x264 using our desktop development host.

1.1 Bit rate and video quality testing
1) Description
We test the different combinations of options which x264 support. We focus on bit rate, frame rate and video quality. Video quality is measured by PSNR (Peak Signal-To-Noise Ratio). PSNR is most commonly used as a measure of q...