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Corwin 2022-10-12 17:06:12 +01:00
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//! There are, broadly speaking, three different kinds of save media that can be
//! found in official Game Carts:
//!
//! * Battery-Backed SRAM: The simplest kind of save media, which can be accessed
//! like normal memory. You can have SRAM up to 32KiB, and while there exist a
//! few variants this does not matter much for a game developer.
//! * Battery-Backed SRAM: The simplest kind of save media, which can be
//! accessed like normal memory. You can have SRAM up to 32KiB, and while
//! there exist a few variants this does not matter much for a game developer.
//! * EEPROM: A kind of save media based on very cheap chips and slow chips.
//! These are accessed using a serial interface based on reading/writing bit
//! streams into IO registers. This memory comes in 8KiB and 512 byte versions,
//! which unfortunately cannot be distinguished at runtime.
//! * Flash: A kind of save media based on flash memory. Flash memory can be read
//! like ordinary memory, but writing requires sending commands using multiple
//! IO register spread across the address space. This memory comes in 64KiB
//! and 128KiB variants, which can thankfully be distinguished using a chip ID.
//! streams into IO registers. This memory comes in 8KiB and 512 byte
//! versions, which unfortunately cannot be distinguished at runtime.
//! * Flash: A kind of save media based on flash memory. Flash memory can be
//! read like ordinary memory, but writing requires sending commands using
//! multiple IO register spread across the address space. This memory comes in
//! 64KiB and 128KiB variants, which can thankfully be distinguished using a
//! chip ID.
//!
//! As these various types of save media cannot be easily distinguished at
//! runtime, the kind of media in use should be set manually.
@ -39,24 +40,26 @@
//!
//! ## Using save media
//!
//! To access save media, use the [`SaveManager::access`] or [`SaveManager::access_with_timer`] methods to create a new
//! [`SaveData`] object. Its methods are used to read or write save media.
//! To access save media, use the [`SaveManager::access`] or
//! [`SaveManager::access_with_timer`] methods to create a new [`SaveData`]
//! object. Its methods are used to read or write save media.
//!
//! Reading data from the savegame is simple. Use [`read`] to copy data from an
//! offset in the savegame into a buffer in memory.
//!
//! Writing to save media requires you to prepare the area for writing by calling
//! the [`prepare_write`] method to return a [`SavePreparedBlock`], which contains
//! the actual [`write`] method.
//! Writing to save media requires you to prepare the area for writing by
//! calling the [`prepare_write`] method to return a [`SavePreparedBlock`],
//! which contains the actual [`write`] method.
//!
//! The `prepare_write` method leaves everything in a sector that overlaps the
//! range passed to it in an implementation defined state. On some devices it may
//! do nothing, and on others, it may clear the entire range to `0xFF`.
//! range passed to it in an implementation defined state. On some devices it
//! may do nothing, and on others, it may clear the entire range to `0xFF`.
//!
//! Because writes can only be prepared on a per-sector basis, a clear on a range
//! of `4000..5000` on a device with 4096 byte sectors will actually clear a range
//! of `0..8192`. Use [`sector_size`] to find the sector size, or [`align_range`]
//! to directly calculate the range of memory that will be affected by the clear.
//! Because writes can only be prepared on a per-sector basis, a clear on a
//! range of `4000..5000` on a device with 4096 byte sectors will actually clear
//! a range of `0..8192`. Use [`sector_size`] to find the sector size, or
//! [`align_range`] to directly calculate the range of memory that will be
//! affected by the clear.
//!
//! [`read`]: SaveData::read
//! [`prepare_write`]: SaveData::prepare_write
@ -78,9 +81,9 @@
//! * Atmel flash chips have a sector size of 128 bytes. Reads to any alignment
//! are efficient, however, unaligned writes are extremely slow.
//! `prepare_write` does not immediately erase any data.
//! * EEPROM has a sector size of 8 bytes. Unaligned reads and writes are
//! slower than aligned writes, however, this is easily mitigated by the
//! small sector size.
//! * EEPROM has a sector size of 8 bytes. Unaligned reads and writes are slower
//! than aligned writes, however, this is easily mitigated by the small sector
//! size.
use crate::save::utils::Timeout;
use crate::sync::{Mutex, RawMutexGuard};