Changes

== RAM management ==

No matter what module is banked into memory, there is a section of memory 4,340 bytes long (0x10F4 bytes) that is reserved for all the variables for the entire game. This entire image is called the "[[FF7/Savemap|Savemap]]". When it's time to save a game, this section of memory is copied to non-volatile ram, such as a hard disk or memory card.

Within the [[FF7/Savemap|Savemap]] there are 5 banks of memory that are directly accessible by the [[FF7/Field_script|field scripting language]]. These can either be accessed 8 bits or 16 bits at a time depending on the field command argument. The following table is basic memory map of the banks and how they relate to the [[FF7/Savemap|Savemap]]. There is also an allocation for 256 bytes for temporary field variables. These are not used between field files and are not saved.

<table CELLSPACING{| class="0wikitable"><tr><th | style="borderbackground: 1px solid rgb(0255, 0255, 0255); width: 68px; height: 43px; background-color: rgb(230, 230, 230);80px">Offset<| N/th>A<th | style="borderbackground: 1px solid rgb(0255, 0255, 0255); text-width: 80px" align: ="center; vertical-align: middle; width: 83px; height: 43px; background-color: rgb(230, 230, 230);">| 0x58 Bit Field Bank</th><th | style="borderbackground: 1px solid rgb(0255, 0255, 0255); text-width: 100px" align: ="center; vertical-align: middle; width: 99px; height: 43px; background-color: rgb(230, 230, 230);">16 Bit Field Bank</th>| 0x6<th | style="borderbackground: 1px solid rgb(0255, 0255, 0255); width: 281px; height: 43px; background-color: rgb250px" | Temporary field variables (230, 230, 230256 bytes);">Description</th></tr>|}

<tr><td style="border: 1px solid rgb(0, 0, 0); width: 68px; height: 25px;">0x0000</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 83px; height: 25px;">N/A</td><td style VRAM management ="border: 1px solid rgb(0, 0, 0); text-align: center; width: 99px; height: 25px;">N/A</td><td style="border: 1px solid rgb(0, 0, 0); width: 281px; height: 25px;">Beginning of Save Map</td></tr>

<tr><td style="border: 1px solid rgb(0The kernel is in charge of allocating, 0caching, 0); width: 68px; height: 25px; background-color: rgb(152and displaying in Video RAM. In the case of the PSX, 204port, 255);">0x0BA4</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 83px; height: 25px; background-color: rgb(152, 204, 255);">0x1</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 99px; height: 25px; background-color: rgb(152, 204, 255);">0x2</td><td style="border: 1px solid rgb(0, 0, 0); width: 281px; height: 25px; background-color: rgb(152, 204, 255);">Field Script Bank the Playstation only has 1</td></tr>megabyte of VRAM which makes this task a little complex. This is alleviated somewhat by using the PSX's VRAM caching system.

<tr><td style=The PSX video memory can best be seen as a rectangular "border: 1px solid rgb(0, 0, 0); width: 68px; height: 25px; background-color: rgb(152, 204, 255);">0x0CA4</td><td style=surface"border: 1px solid rgb(0, 0, 0); text-align: center; width: 83px; height: 25px; background-made up of 2048x512 pixels. A slight caveat to this model is that the PSX can hold multiple color: rgb(152, 204depths in VRAM at the same time. To make the VRAM a little easier to visualize, 255);">0x3</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 99px; height: 25px; background-This document represents VRAM as a 1024x512 matrix to allow for some color: rgb(152, 204, 255);">0x4</td><td style="border: 1px solid rgb(0, 0, 0); width: 281px; height: 25px; background-color: rgb(152, 204, 255);">Field Script Bank 2</td></tr>depth in either direction and to minimize some extreme skewing of the video buffers.

<tr><td style="border: 1px solid rgb(0, 0, 0); width: 68px; height: 25px; background-color: rgb(152, 204, 255);">0x0DA4</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 83px; height: 25px; background-color: rgb(152, 204, 255);">0xB</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 99px; height: 25px; background-color: rgb(152, 204, 255);">0xC</td><td style="border: 1px solid rgb(0, 0, 0); width: 281px; height: 25px; background-color: rgb(152, 204, 255);">Field Script Bank 3</td><br /tr>The following is a typical state of VRAM during game play.

<tr><td style="border: 1px solid rgb(0, 0, 0); width: 68px; height: 25px; background-color: rgb(152, 204, 255);">0x0EA4</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 83px; height: 25px; background-color: rgb(152, 204, 255);">0xD</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 99px; height: 25px; background-color: rgb(152, 204, 255);">0xE</td><td style="border: 1px solid rgb(0, 0, 0); width: 281px; height: 25px; background-color: rgb(152, 204, 255);">Field Script Bank 4</td></tr> <tr><td style="border: 1px solid rgb(0, 0, 0); width: 68px; height: 25px; background-color: rgb(152, 204, 255);">0x0FA4</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 83px; height: 25px; background-color: rgb(152, 204, 255);">0x7</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 99px; height: 25px; background-color: rgb(152, 204, 255);">0xF</td><td style="border: 1px solid rgb(0, 0, 0); width: 281px; height: 25px; background-color: rgb(152, 204, 255);">Field Script Bank 5</td></tr> <tr><td style="border: 1px solid rgb(0, 0, 0); width: 68px; height: 25px;">0x10F4</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 83px; height: 25px;">N/A</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 99px; height: 25px;">N/A</td><td style="border: 1px solid rgb(0, 0, 0); width: 281px; height: 25px;">End of Save Map</td></tr> <tr><td style="border-style: solid none solid solid; border-color: rgb(0, 0, 0); border-width: 1px; vertical-align: top; width: 68px; height: 25px;"></td><td style="border-style: solid none; border-color: rgb(0, 0, 0); border-width: 1px; text-align: center; vertical-align: top; width: 83px; height: 25px;"></td><td style="border-style: solid none; border-color: rgb(0, 0, 0); border-width: 1px; text-align: center; vertical-align: top; width: 99px; height: 25px;"></td><td style="border-style: solid solid solid none; border-color: rgb(0, 0, 0); border-width: 1px; vertical-align: top; width: 281px; height: 25px;"></td></tr> <tr><td style="border: 1px solid rgb(0, 0, 0); width: 68px; height: 25px;">N/A</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 83px; height: 25px;">0x5</td><td style="border: 1px solid rgb(0, 0, 0); text-align: center; width: 99px; height: 25px;">0x6</td><td style="border: 1px solid rgb(0, 0, 0); width: 281px; height: 25px;">Temporary field variables (256 bytes)</td></tr></table>  A more complete and annotated save map is in the MENU section.   == VRAM management == The kernel is in charge of allocating, caching, and displaying in Video RAM. The the case if the PSX, port, the Playstation only has 1 megabyte of VRAM which makes this task a little complex. This is alleviated somewhat by using the PSX's VRAM caching system. The PSX video memory can best be seen as a rectangular "surface" made up of 2048x512 pixels. A slight caveat to this model is that the PSX can hold multiple color depths in VRAM at the same time. To make the VRAM a little easier to visualize, This document represents VRAM as a 1024x512 matrix to allow for some color depth in either direction and to minimize some extreme skewing of the video buffers.   The following is a typical state of VRAM during game play. [[ImageFile:Gears_img_3Gears img 3.jpg|thumb]]

The following is a schematic representation of VRAM and all it's texture boundaries. [[ImageFile:Gears_img_4Gears img 4.jpg|thumb]]

The magenta area under the video buffers is the Color Look Up Tables (CLUT). This is where the texture palettes are stored. This is also allows the PSX to display multiple color depths at the same time. The red area to the right is extra CLUT space when it is needed and there are no textures cached there.

== PSX CD-ROM management ==One of the big rules on PSX development is that direct hardware access is a prohibited. Everything must go through the BIOS or the program will risk being incompatible with later systems. This means not only the from PSX to PS2, but also all the trivial hardware revisions as well. This creates a problem for the kernel. During module transitions, (For for example, going from "Map" to "Battle"), the engine actually "preloads" the next module while the current one is still executing. This loading of data can't be done with a simple open() or read() BIOS syscall. Whenever you enter the BIOS, the rest of the system comes to a screeching halt until it is exited.