It just gives the game some memory to work with and assumes the game will play nice. MMU Off is as barebones as MMU emulation can get while still booting games. The other thing to note is the special boot sector, but since games can't access it there isn't much more to say about it for now. The big one is Memory-Mapped Input/Output (MMIO), which is how the CPU interacts with different devices, such as the disc drive, memory cards, etc. There are also a few other major pieces mapped out that we'll be keeping out of the scope of this article. In layman's terms, the game is asking for one memory address, but the console (and thus Dolphin) gives it another from real memory. Because BATs are faster than page tables, most games simply stick to this.ĭolphin's way of handling this is to hardcode that Block Address Translation (BAT) from virtual memory and translate the address to physical memory. The default mappings have one Block Address Translation (BAT) that translates to all of physical memory. Most games use the GameCube/Wii's default BAT mappings, and as long as they don't try to access memory outside of that, all that has to be done is making sure accesses end up in the right place.
#Dolphin emulator gamecube star bios software
Theory 1: The Software Only Writes to Valid Memory ¶Īs long as the games only write to valid memory, Dolphin doesn't have much work to do. Secondly, the GameCube only has 24MB (and some specialized areas) of RAM across a 4GB address space, meaning most memory addresses have no RAM backing them! If a game were to access a real memory address with no backing memory, it'd get garbage or even crash! By using virtual memory, the MMU can throw an exception giving the game a way to handle the situation or provide valuable feedback to developers on what went wrong.ĭolphin is able to emulate the MMU with several degrees of accuracy based on theories of how the game is going to behave.
First of all, it gives the CPU an opportunity to cache accesses, greatly speeding up the efficiency of accessing often used values. The games are given access to virtual memory instead of real memory for several reasons. This can be done in two ways, with Block Address Translations (BATs) for huge portions of memory or the page tables for small fine-grained mappings.
Rather than directly accessing available RAM, games interface with virtual memory which is then translated to physical memory by the MMU. The Memory Management Unit, or MMU, is responsible for quickly giving games access to data and code.
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