avclk

Avclk, short for audio/video clock, is a foundational timing signal used to synchronize the digital audio and video subsystems within multimedia devices. It provides a common reference that drives components such as audio codecs, DACs and ADCs, video encoders and decoders, display interfaces, and memory controllers, helping to coordinate data flow and timing across the AV pipeline.

Generation and distribution

Avclk is typically produced by a clock generator or a phase-locked loop (PLL) within the system, and is routed through a clock tree to various blocks. Depending on the design, there may be a single master avclk or multiple related clock domains (for example avclk for audio, vidclk for video, and separate domain clocks for memory and I/O). The clock may be fixed or dynamically adjusted to match changing modes, resolutions, or sample rates. Proper distribution often involves clock gating, domain crossing considerations, and careful synchronization to minimize jitter and drift.

Role in synchronization

A primary purpose of avclk is to maintain lip synchronization between audio and video streams. Deviations in clock frequencies can lead to audio gaps, video stuttering, or misaligned frames. To mitigate this, systems may employ clock management techniques, buffer strategies, and, when necessary, asynchronous sample rate conversion or resampling to preserve AV alignment.

Implementation notes

In software and firmware, avclk is commonly exposed through a clock framework or device tree description, allowing drivers to enable, configure, or gate the clock as needed. Misconfiguration can cause audio dropouts or video instability, so correct setup of the clock source, frequency, and gating is essential for reliable multimedia operation.