This document describes the environment in which games and applications run inside the PlayStation 3 and Nucleus approach to emulate it. The PlayStation 3 boot process after FW 3.60 is managed by LV0, which encapsulates all loaders (appldr, isoldr, lv1ldr, lv2ldr). LV1, formally Cell OS Lv-1, provides the logical partitions, and the resource handling to the underlying operating system. LV2, formally Cell OS Lv-2, provides a software execution environment with process management and thread synchronization primitives and communicates with LV1 through hvsc or sc, 1. Finally, user process can communicate with LV2 through sc or sc, 0. LV1 code runs in Hypervisor Mode, LV2 code runs in Supervisor Mode and user processes run in User Mode.
Since performance on a PS3 emulator is the biggest challenge, Nucleus is designed as a High-Level Emulator (HLE), providing the User Mode environment by intercepting syscalls and replacing them with a native custom LV2 kernel. This makes LV1 and the booting process irrelevant for us. System libraries are Low-Level Emulated (LLE), that is, dynamically loaded into memory, linked and run as part of the game.
A few points to take into account are:
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Games and applications cannot spawn multiple processes, therefore Nucleus focuses in emulating one process. However, games can use Inter-Process Communication (IPC) with system process like vsh.self (e.g. via the libsysutil.sprx module). An approach for this is explained below.
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To deal with performance issues in hardware intensive system modules (e.g. image/audio/video decoding modules), or bypassing IPC queries (rarely used by the application directly), some system library functions are HLE'd instead of LLE'd.
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For the sake of resembling a bit more the original PS3, some RSX-related LV2 syscalls have their implementation splitted in the syscalls/lv1 and syscalls/lv2 folders. For now, there is no further meaning in this.