Up to this point, we've discussed the main CPU and the buses inside Tachyon, but there are still many features to be found in the SoC. In particular, there's another block of modules designed for a specific application: multimedia. This group specialises in audio and image processing, including the combination of both (video processing), and it operates without consuming bandwidth from the main CPU bus (the 'system group').
Daxter (2006), showing an in-game cinematic rendered by the Media Engine group.
This new block is called Media Engine group and it's composed of the following components:
- A second Allegrex CPU serving as the 'controller' of the Media Engine group. This is the same CPU found in the system group, but without the vector coprocessor . The controller is responsible for receiving orders from the main CPU and managing the rest of the multimedia hardware that will work concurrently.
- 2 MB of embedded DRAM (eDRAM): multimedia encoding and/or decoding consumes a considerable amount of bandwidth, so to avoid stalling the other components, the Media Engine contains dedicated memory to process the data 'in-house' and publish the results when necessary.
- 'eDRAM' is the same as DRAM but manufactured inside another chip.
- An MPEG-AVC decoder: a hardware decoder that does only one thing, and fast. That is, swallow an H.264 video stream and spit out data that the audio and graphics endpoint understand.
- A Virtual Mobile Engine or 'VME': this is some sort of programmable Digital Signal Processor (DSP). The controller programs it and then begins feeding in the data. Afterwards, like the AVC, the VME stores the processed chunk in local memory.
- This is a very obscure component; only Sony seems to know the ins and outs of it (including how to program it). To this day, it's still a mystery.
- Based on unofficial reports, the VME seems to have local memory and a DMA controller. It's also known as the 'Dynamic Reconfigurable Engine' .
Needless to say, the Media Engine is not directly operable from the developer's side (Sony hides all of it through a thick API). The operating system provides frameworks like 'libmpeg' or 'libmp3' that already implement complete applications optimised for this engine .