EE, IOP, and SIF

This section is in beta. See the note on the cheat sheet.

The EE and the IOP do not share memory. Game logic runs on the EE, and almost every peripheral is reachable only from the IOP. This page documents the link between them.

IOP modules

An IOP module (.irx) is a separate program with its own entry point (_start), loaded into the IOP's memory by the IOP's kernel. It is not linked into your EE executable. A ps2.yaml iop/iop_lib target builds one of these. Your EE executable and its IOP modules are separate binaries that cooperate at runtime. Consequences:

• embed_irx exists. It bundles a companion .irx into an ee target, so ps2build build produces one .elf and you do not ship multiple files.
• many packages come in pairs. One half is an EE-side library that gives your game code an ordinary function to call. The other half is the IOP driver that function talks to over SIF. pad+padman, mc+mcman/mcserv, netman (IOP side) paired with ps2ip (EE side) all follow this pattern.

SIF

SIF (Sub-system InterFace) is the hardware link between the two processors. It is a narrow channel with no shared memory. This SDK's sifman/sifcmd packages are the software RPC layer built on top of it: sifman handles the low-level init/DMA-transfer mechanics, sifcmd layers a request/response RPC protocol over that so EE code can call sceSifCallRpc()-style functions that block until the IOP module on the other end replies.

Two of the ten DMA channels are dedicated to this link (DMA_CHANNEL_fromSIF0/DMA_CHANNEL_toSIF1 - see DMA), plus a less-common third (DMA_CHANNEL_SIF2).

RPC calls and loading

An RPC call sends a message to the IOP and back and costs more than a local function call. An IOP module must be loaded (SifLoadModule or SifExecModuleBuffer, or embed_irx, which bundles it into the EE binary) before anything can call into it. Linking is not enough.

patches (sbv)

The patches package (source directory sbv, see the cheat sheet) exists because some IOP features the SDK relies on, such as loading a module from an in-memory buffer instead of a file, are missing from the original retail BIOS's IOP kernel. Most programs call sbv_patch_enable_lmb() before any other IOP work. It patches the running IOP kernel to support LoadModuleBuffer.

See also

• DMA
• Introduction to PS2 architecture