PCSX2 Documentation/MMU mini-series: Difference between revisions
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Let's begin with the root, the Operating System (OS). Hardware can run without any OS but it is often a necessary evil. The OS has 2 major goals: | Let's begin with the root, the Operating System (OS). Hardware can run without any OS but it is often a necessary evil. The OS has 2 major goals: | ||
1 | 1. The first goal of the OS is to control privilege access of processes. | ||
Maybe you want to keep a resource for the hardware or OS internal, for example a hardware watchdog. Maybe you only want to check the validity of a command. It could be as simple as only allowing a stop command after a start command. | Maybe you want to keep a resource for the hardware or OS internal, for example a hardware watchdog. Maybe you only want to check the validity of a command. It could be as simple as only allowing a stop command after a start command. | ||
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As you can see, without any OS you could easily kill your system. The OS allows the separation of privileged and standard resources. | As you can see, without any OS you could easily kill your system. The OS allows the separation of privileged and standard resources. | ||
2 | 2. The second goal is to share the resources between processes | ||
You need to understand that processes are independent for coding simplicity and security. | You need to understand that processes are independent for coding simplicity and security. | ||
Let's reuse our hardware counter example | Let's reuse our hardware counter example | ||
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* The first 512KB of RAM is not virtually mapped because it is at the location of the OS, do you know how the kernel will access this location? | * The first 512KB of RAM is not virtually mapped because it is at the location of the OS, do you know how the kernel will access this location? | ||
* A hardware component needs to access the memory without the CPUs intervention. Do you know which one? Do you know how the addresses are handled? | * A hardware component needs to access the memory without the CPUs intervention. Do you know which one? Do you know how the addresses are handled? | ||
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