ABelliqueux
/
psx-spx.github.io
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity
psx-spx.github.io/memorymap/index.html

573 lines
26 KiB
HTML
Raw Blame History

<!DOCTYPE html>
<html class="no-js" lang="en">
<head>
<meta charset="utf-8"/>
<meta content="width=device-width,initial-scale=1" name="viewport"/>
<link href="https://psx-spx.consoledev.net/memorymap/" rel="canonical"/>
<link href="../assets/images/favicon.png" rel="icon"/>
<meta content="mkdocs-1.1.2, mkdocs-material-7.1.3" name="generator"/>
<title>Memory Map - PlayStation Specifications - psx-spx</title>
<link href="../assets/stylesheets/main.e35208c4.min.css" rel="stylesheet"/>
<link href="../assets/stylesheets/palette.ef6f36e2.min.css" rel="stylesheet"/>
<link crossorigin="" href="https://fonts.gstatic.com" rel="preconnect"/>
<link href="https://fonts.googleapis.com/css?family=Roboto:300,400,400i,700%7CRoboto+Mono&amp;display=fallback" rel="stylesheet"/>
<style>:root{--md-text-font-family:"Roboto";--md-code-font-family:"Roboto Mono"}</style>
<link href="../css/extra.css" rel="stylesheet"/>
</head>
<body data-md-color-accent="indigo" data-md-color-primary="indigo" data-md-color-scheme="default" dir="ltr">
<script>function __prefix(e){return new URL("..",location).pathname+"."+e}function __get(e,t=localStorage){return JSON.parse(t.getItem(__prefix(e)))}</script>
<script>var palette=__get("__palette");if(null!==palette&&"object"==typeof palette.color)for(var key in palette.color)document.body.setAttribute("data-md-color-"+key,palette.color[key])</script>
<input autocomplete="off" class="md-toggle" data-md-toggle="drawer" id="__drawer" type="checkbox"/>
<input autocomplete="off" class="md-toggle" data-md-toggle="search" id="__search" type="checkbox"/>
<label class="md-overlay" for="__drawer"></label>
<div data-md-component="skip">
<a class="md-skip" href="#memory-map">
Skip to content
</a>
</div>
<div data-md-component="announce">
</div>
<header class="md-header" data-md-component="header">
<nav aria-label="Header" class="md-header__inner md-grid">
<a aria-label="PlayStation Specifications - psx-spx" class="md-header__button md-logo" data-md-component="logo" href=".." title="PlayStation Specifications - psx-spx">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54z"></path></svg>
</a>
<label class="md-header__button md-icon" for="__drawer">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M3 6h18v2H3V6m0 5h18v2H3v-2m0 5h18v2H3v-2z"></path></svg>
</label>
<div class="md-header__title" data-md-component="header-title">
<div class="md-header__ellipsis">
<div class="md-header__topic">
<span class="md-ellipsis">
PlayStation Specifications - psx-spx
</span>
</div>
<div class="md-header__topic" data-md-component="header-topic">
<span class="md-ellipsis">
Memory Map
</span>
</div>
</div>
</div>
<form class="md-header__option" data-md-component="palette">
<input class="md-option" data-md-color-accent="indigo" data-md-color-media="(prefers-color-scheme: light)" data-md-color-primary="indigo" data-md-color-scheme="default" id="__palette_1" name="__palette" type="radio"/>
<label class="md-header__button md-icon" for="__palette_2" hidden="" title="Switch to dark mode">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M7 10a2 2 0 0 1 2 2 2 2 0 0 1-2 2 2 2 0 0 1-2-2 2 2 0 0 1 2-2m10-3a5 5 0 0 1 5 5 5 5 0 0 1-5 5H7a5 5 0 0 1-5-5 5 5 0 0 1 5-5h10M7 9a3 3 0 0 0-3 3 3 3 0 0 0 3 3h10a3 3 0 0 0 3-3 3 3 0 0 0-3-3H7z"></path></svg>
</label>
<input class="md-option" data-md-color-accent="blue" data-md-color-media="(prefers-color-scheme: dark)" data-md-color-primary="blue" data-md-color-scheme="slate" id="__palette_2" name="__palette" type="radio"/>
<label class="md-header__button md-icon" for="__palette_1" hidden="" title="Switch to light mode">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M17 7H7a5 5 0 0 0-5 5 5 5 0 0 0 5 5h10a5 5 0 0 0 5-5 5 5 0 0 0-5-5m0 8a3 3 0 0 1-3-3 3 3 0 0 1 3-3 3 3 0 0 1 3 3 3 3 0 0 1-3 3z"></path></svg>
</label>
</form>
<label class="md-header__button md-icon" for="__search">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5z"></path></svg>
</label>
<div class="md-search" data-md-component="search" role="dialog">
<label class="md-search__overlay" for="__search"></label>
<div class="md-search__inner" role="search">
<form class="md-search__form" name="search">
<input aria-label="Search" autocapitalize="off" autocomplete="off" autocorrect="off" class="md-search__input" data-md-component="search-query" data-md-state="active" name="query" placeholder="Search" required="" spellcheck="false" type="text"/>
<label class="md-search__icon md-icon" for="__search">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5z"></path></svg>
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12z"></path></svg>
</label>
<button aria-label="Clear" class="md-search__icon md-icon" tabindex="-1" type="reset">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M19 6.41 17.59 5 12 10.59 6.41 5 5 6.41 10.59 12 5 17.59 6.41 19 12 13.41 17.59 19 19 17.59 13.41 12 19 6.41z"></path></svg>
</button>
</form>
<div class="md-search__output">
<div class="md-search__scrollwrap" data-md-scrollfix="">
<div class="md-search-result" data-md-component="search-result">
<div class="md-search-result__meta">
Initializing search
</div>
<ol class="md-search-result__list"></ol>
</div>
</div>
</div>
</div>
</div>
<div class="md-header__source">
<a class="md-source" data-md-component="source" href="https://github.com/psx-spx/psx-spx.github.io/" title="Go to repository">
<div class="md-source__icon md-icon">
<svg viewbox="0 0 448 512" xmlns="http://www.w3.org/2000/svg"><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81z"></path></svg>
</div>
<div class="md-source__repository">
GitHub
</div>
</a>
</div>
</nav>
</header>
<div class="md-container" data-md-component="container">
<main class="md-main" data-md-component="main">
<div class="md-main__inner md-grid">
<div class="md-sidebar md-sidebar--primary" data-md-component="sidebar" data-md-type="navigation">
<div class="md-sidebar__scrollwrap">
<div class="md-sidebar__inner">
<nav aria-label="Navigation" class="md-nav md-nav--primary" data-md-level="0">
<label class="md-nav__title" for="__drawer">
<a aria-label="PlayStation Specifications - psx-spx" class="md-nav__button md-logo" data-md-component="logo" href=".." title="PlayStation Specifications - psx-spx">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54z"></path></svg>
</a>
PlayStation Specifications - psx-spx
</label>
<div class="md-nav__source">
<a class="md-source" data-md-component="source" href="https://github.com/psx-spx/psx-spx.github.io/" title="Go to repository">
<div class="md-source__icon md-icon">
<svg viewbox="0 0 448 512" xmlns="http://www.w3.org/2000/svg"><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81z"></path></svg>
</div>
<div class="md-source__repository">
GitHub
</div>
</a>
</div>
<ul class="md-nav__list" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="..">
Home
</a>
</li>
<li class="md-nav__item md-nav__item--active">
<input class="md-nav__toggle md-toggle" data-md-toggle="toc" id="__toc" type="checkbox"/>
<label class="md-nav__link md-nav__link--active" for="__toc">
Memory Map
<span class="md-nav__icon md-icon"></span>
</label>
<a class="md-nav__link md-nav__link--active" href="./">
Memory Map
</a>
<nav aria-label="Table of contents" class="md-nav md-nav--secondary">
<label class="md-nav__title" for="__toc">
<span class="md-nav__icon md-icon"></span>
Table of contents
</label>
<ul class="md-nav__list" data-md-component="toc" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="#memory-map_1">
Memory Map
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#additional-memory-not-mapped-to-the-cpu-bus">
Additional Memory (not mapped to the CPU bus)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#kusegkseg0kseg1kseg2-memory-regions">
KUSEG,KSEG0,KSEG1,KSEG2 Memory Regions
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#i-cache">
i-Cache
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#scratchpad">
Scratchpad
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#memory-mirrors">
Memory Mirrors
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#memory-exceptions">
Memory Exceptions
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#write-queue">
Write queue
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#more-memory-info">
More Memory Info
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../iomap/">
I/O Map
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../graphicsprocessingunitgpu/">
Graphics Processing Unit (GPU)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../geometrytransformationenginegte/">
Geometry Transformation Engine (GTE)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../macroblockdecodermdec/">
Macroblock Decoder (MDEC)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../soundprocessingunitspu/">
Sound Processing Unit (SPU)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../interrupts/">
Interrupts
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../dmachannels/">
DMA Channels
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../timers/">
Timers
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../cdromdrive/">
CDROM Drive
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../controllersandmemorycards/">
Controllers and Memory Cards
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../pocketstation/">
Pocketstation
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../serialportsio/">
Serial Port (SIO)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../expansionportpio/">
Expansion Port (PIO)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../memorycontrol/">
Memory Control
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../unpredictablethings/">
Unpredictable Things
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../cpuspecifications/">
CPU Specifications
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../kernelbios/">
Kernel (BIOS)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../arcadecabinets/">
Arcade Cabinets
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../cheatdevices/">
Cheat Devices
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../psxdevboardchipsets/">
PSX Dev-Board Chipsets
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../hardwarenumbers/">
Hardware Numbers
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../pinouts/">
Pinouts
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../aboutcredits/">
About &amp; Credits
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../cdromvideocdsvcd/">
CDROM Video CDs (VCD)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="../cdrominternalinfoonpsxcdromcontroller/">
CDROM Internal Info on PSX CDROM Controller
</a>
</li>
</ul>
</nav>
</div>
</div>
</div>
<div class="md-sidebar md-sidebar--secondary" data-md-component="sidebar" data-md-type="toc">
<div class="md-sidebar__scrollwrap">
<div class="md-sidebar__inner">
<nav aria-label="Table of contents" class="md-nav md-nav--secondary">
<label class="md-nav__title" for="__toc">
<span class="md-nav__icon md-icon"></span>
Table of contents
</label>
<ul class="md-nav__list" data-md-component="toc" data-md-scrollfix="">
<li class="md-nav__item">
<a class="md-nav__link" href="#memory-map_1">
Memory Map
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#additional-memory-not-mapped-to-the-cpu-bus">
Additional Memory (not mapped to the CPU bus)
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#kusegkseg0kseg1kseg2-memory-regions">
KUSEG,KSEG0,KSEG1,KSEG2 Memory Regions
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#i-cache">
i-Cache
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#scratchpad">
Scratchpad
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#memory-mirrors">
Memory Mirrors
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#memory-exceptions">
Memory Exceptions
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#write-queue">
Write queue
</a>
</li>
<li class="md-nav__item">
<a class="md-nav__link" href="#more-memory-info">
More Memory Info
</a>
</li>
</ul>
</nav>
</div>
</div>
</div>
<div class="md-content" data-md-component="content">
<article class="md-content__inner md-typeset">
<a class="md-content__button md-icon" href="https://github.com/psx-spx/psx-spx.github.io/edit/master/docs/memorymap.md" title="Edit this page">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M20.71 7.04c.39-.39.39-1.04 0-1.41l-2.34-2.34c-.37-.39-1.02-.39-1.41 0l-1.84 1.83 3.75 3.75M3 17.25V21h3.75L17.81 9.93l-3.75-3.75L3 17.25z"></path></svg>
</a>
<h1 id="memory-map">Memory Map</h1>
<h4 id="memory-map_1">Memory Map</h4>
<pre><code> KUSEG KSEG0 KSEG1
00000000h 80000000h A0000000h 2048K Main RAM (first 64K reserved for BIOS)
1F000000h 9F000000h BF000000h 8192K Expansion Region 1 (ROM/RAM)
1F800000h 9F800000h -- 1K Scratchpad (D-Cache used as Fast RAM)
1F801000h 9F801000h BF801000h 8K I/O Ports
1F802000h 9F802000h BF802000h 8K Expansion Region 2 (I/O Ports)
1FA00000h 9FA00000h BFA00000h 2048K Expansion Region 3 (SRAM BIOS region for DTL cards)
1FC00000h 9FC00000h BFC00000h 512K BIOS ROM (Kernel) (4096K max)
FFFE0000h (in KSEG2) 0.5K Internal CPU control registers (Cache Control)
</code></pre>
<p>Additionally, there are a number of memory mirrors.<br/></p>
<h4 id="additional-memory-not-mapped-to-the-cpu-bus">Additional Memory (not mapped to the CPU bus)</h4>
<pre><code> 1024K VRAM (Framebuffers, Textures, Palettes) (with 2KB Texture Cache)
512K Sound RAM (Capture Buffers, ADPCM Data, Reverb Workspace)
0.5K CDROM controller RAM (see CDROM Test commands)
16.5K CDROM controller ROM (Firmware and Bootstrap for MC68HC05 cpu)
32K CDROM Buffer (IC303) (32Kx8) (BUG: only two sectors accessible?)
128K External Memory Card(s) (EEPROMs)
</code></pre>
<h4 id="kusegkseg0kseg1kseg2-memory-regions">KUSEG,KSEG0,KSEG1,KSEG2 Memory Regions</h4>
<pre><code> Address Name i-Cache Write-Queue
00000000h KUSEG Yes Yes
80000000h KSEG0 Yes Yes
A0000000h KSEG1 No No
C0000000h KSEG2 (No code) No
</code></pre>
<p>Kernel Memory: KSEG1 is the normal physical memory (uncached), KSEG0 is a
mirror thereof (but with cache enabled). KSEG2 is usually intended to contain
virtual kernel memory, but in the PSX it's containing Cache Control hardware registers.<br/>
User Memory: KUSEG is intended to contain 2GB virtual memory (on extended MIPS
processors), the PSX doesn't support virtual memory, and KUSEG simply contains
a mirror of KSEG0/KSEG1 (in the first 512MB) (trying to access memory in the
remaining 1.5GB causes an exception).<br/></p>
<h4 id="i-cache">i-Cache</h4>
<p>The i-Cache can hold 4096 bytes, or 1024 instructions.<br/>
It is only active in the cached regions (KUSEG and KSEG0).<br/>
There are reportedly some restrictions... not sure there... eventually it is
using the LSBs of the address as cache-line number... so, for example, it
couldn't simultaneously memorize opcodes at BOTH address 80001234h, AND at
address 800F1234h (?)<br/></p>
<h4 id="scratchpad">Scratchpad</h4>
<p>MIPS CPUs usually have a d-Cache, but, in the PSX, Sony has assigned it as
what's referenced as the "Scratchpad", mapped to a fixed memory location at
1F800000h..1F8003FFh, ie. it's used as Fast RAM, rather than as cache.<br/>
There \&lt;might&gt; be a way to disable that behavior (via Port FFFE0130h or
so), but, the Kernel is accessing I/O ports via KUSEG, so activating Data Cache
would cause the Kernel to access cached I/O ports.<br/>
The purpose of the scratchpad is to have a more flexible cache system available
to the programmer. Neither the kernel nor the Sony libraries will try to make use
of it, so it is therefore completely up for grabs to the programmer. A good example
would be if you were to write a piece of code that's doing a lot of CRC computation,
to use the 1KB scratchpad to initially load the CRC lookup tables, which incidentally,
is exactly 1KB large. Doing this will relieve SDRAM page changes overhead while reading
the data to checksum linearly, while also keeping the whole CRC code in the i-Cache,
hence being more optimal than what you'd get with an automatic d-Cache system.</p>
<h4 id="memory-mirrors">Memory Mirrors</h4>
<p>As described above, the 512Mbyte KUSEG, KSEG0, and KSEG1 regions are mirrors of
each other. Additional mirrors within these 512MB regions are:<br/></p>
<pre><code> 2MB RAM can be mirrored to the first 8MB (strangely, enabled by default)
512K BIOS ROM can be mirrored to the last 4MB (disabled by default)
Expansion hardware (if any) may be mirrored within expansion region
The seven DMA Control Registers at 1F8010x8h are mirrored to 1F8010xCh
</code></pre>
<p>The size of the RAM, BIOS, Expansion regions can be configured by software, for
Expansion Region it's also possible to change base address, see:<br/>
<a href="../memorycontrol/">Memory Control</a><br/>
The Scratchpad is mirrored only in KUSEG and KSEG0, but not in KSEG1.<br/></p>
<h4 id="memory-exceptions">Memory Exceptions</h4>
<pre><code> Memory Error ------&gt; Misalignments
(and probably also KSEG access in User mode)
Bus Error ------&gt; Unused Memory Regions (including Gaps in I/O Region)
(unless RAM/BIOS/Expansion mirrors are mapped to "unused" area)
</code></pre>
<h4 id="write-queue">Write queue</h4>
<p>The MIPS CPU has a 4-words deep pass-through write queue, in order to relieve
some bus contention when writing to memory. If reading the same memory location
that just got written into the write queue, it will first be flushed before
being read back from memory.<br/>
It is important to realize that the write queue's mechanism is only viable for
normal memory attached to the main CPU, and that any hardware register state machine
will get messed up by it.<br/>
The typical example is the typical JEDEC standard to access flash, which usually does
the following sequence to read the ID of a flash chip:</p>
<pre><code class="language-C"> base[0xAAA] = 0xAA;
base[0x555] = 0x55;
base[0xAAA] = 0x90;
uint8_t mnfctrID = base[0x000];
uint8_t deviceId = base[0x002];
</code></pre>
<p>In this example above, if <code>base</code> is located in a memory segment that has the write queue
enabled, even if the low level assembly code will do the first 3 stores before doing 2 loads,
the physical signals sent to that device through the CPU bus will be seen in the sequence:</p>
<pre><code>store(0xaaa, 0xaa)
load(0x000)
store(0x555, 0x55)
load(0x002)
store(0xaaa, 0x90)
</code></pre>
<p>Therefore, using KSEG1 that disables the write queue is the only way to ensure that the
operations are done in the proper way.</p>
<p>The above is valid for most of the hardware connected to the main CPU, such as the CDROM
controller, exp1, exp2, the SPU, or the GPU. Therefore, using BF80180xh to access the
CDROM registers is more correct than using 1F80180xh.</p>
<p>It is noteworthy that the Sony code will still incorrectly use KUSEG as the memory map
for all hardware registers, and they then spend a lot of time writing 4 dummy values
somewhere, in order to ensure the write queue has been flushed.</p>
<p>The SN debugger in contrast is properly using the KSEG1 memory map for all the hardware
registers, nullifying the need to flush the write queue when accessing it.</p>
<p>It's also noteworthy that doing ANY KSEG1 access (read OR write) will automatically stall
the CPU in order to flush the whole write queue before proceeding with the operation.
Therefore, all BIOS ROM operations will naturally and effectively have the write queue
disabled, as this code requires the CPU to read from KSEG1 constantly.</p>
<p>This also means that if using KUSEG for the hardware registers, another method to flush
the write queue, albeit potentially slightly less efficient, would be to simply read
the first byte located at BFC00000h. The latter is what is effectively described as the
official method to flush the write queue in the MIPS handbook. This could be potentially
useful to flush the write queue all at once, instead of flushing it word by word.</p>
<h4 id="more-memory-info">More Memory Info</h4>
<p>For Info on Exception vectors, Unused/Garbage memory locations, I/O Ports,
Expansion ROM Headers, and Memory Waitstate Control, etc. see:<br/>
<a href="../iomap/">I/O Map</a><br/>
<a href="../memorycontrol/">Memory Control</a><br/>
<a href="../expansionportpio/#exp1-expansion-rom-header">EXP1 Expansion ROM Header</a><br/>
<a href="../kernelbios/#bios-memory-map">BIOS Memory Map</a><br/>
<a href="../kernelbios/#bios-memory-allocation">BIOS Memory Allocation</a><br/>
<a href="../cpuspecifications/#cop0-exception-handling">COP0 - Exception Handling</a><br/>
<a href="../unpredictablethings/">Unpredictable Things</a><br/></p>
</article>
</div>
</div>
</main>
<footer class="md-footer">
<nav aria-label="Footer" class="md-footer__inner md-grid">
<a class="md-footer__link md-footer__link--prev" href=".." rel="prev">
<div class="md-footer__button md-icon">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12z"></path></svg>
</div>
<div class="md-footer__title">
<div class="md-ellipsis">
<span class="md-footer__direction">
Previous
</span>
Home
</div>
</div>
</a>
<a class="md-footer__link md-footer__link--next" href="../iomap/" rel="next">
<div class="md-footer__title">
<div class="md-ellipsis">
<span class="md-footer__direction">
Next
</span>
I/O Map
</div>
</div>
<div class="md-footer__button md-icon">
<svg viewbox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11H4z"></path></svg>
</div>
</a>
</nav>
<div class="md-footer-meta md-typeset">
<div class="md-footer-meta__inner md-grid">
<div class="md-footer-copyright">
Made with
<a href="https://squidfunk.github.io/mkdocs-material/" rel="noopener" target="_blank">
Material for MkDocs
</a>
... <a class="link--pdf-download" download href="../psx-spx.pdf" title="PDF">download PDF</a></div>
</div>
</div>
</footer>
</div>
<div class="md-dialog" data-md-component="dialog">
<div class="md-dialog__inner md-typeset"></div>
</div>
<script id="__config" type="application/json">{"base": "..", "features": [], "translations": {"clipboard.copy": "Copy to clipboard", "clipboard.copied": "Copied to clipboard", "search.config.lang": "en", "search.config.pipeline": "trimmer, stopWordFilter", "search.config.separator": "[\\s\\-]+", "search.placeholder": "Search", "search.result.placeholder": "Type to start searching", "search.result.none": "No matching documents", "search.result.one": "1 matching document", "search.result.other": "# matching documents", "search.result.more.one": "1 more on this page", "search.result.more.other": "# more on this page", "search.result.term.missing": "Missing"}, "search": "../assets/javascripts/workers/search.fe42c31b.min.js", "version": null}</script>
<script src="../assets/javascripts/bundle.4ea5477f.min.js"></script>
</body>
</html>
Reference in New Issue View Git Blame Copy Permalink