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Dr-Noob
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# cpufetch programming documentation (v0.88)
# cpufetch programming documentation (v0.94)
This documentation explains how cpufetch works internally and all the design decisions I made. The intention of this documentation is to be useful for me in the future, for everyone interested in the project, and for anyone who is trying to obtain any specific information from the CPU. In this way, this can be used as a manual or a page which collects interesting material in this area.
### 1. Basics
cpufetch works for __x86_64__ CPUs (Intel and AMD) and experimental support for __ARM__. Other kinds of x86_64 CPU are not supported (I don't think supporting other CPUs may pay off). Depending on the architecture, cpufetch choose certain files to be compiled. A summarized tree of the source code of cpufetch is shown below.
cpufetch works for __x86_64__ (Intel and AMD) and __ARM__ CPUs. However, cpufetch is expected to work better on x86_64, because the codebase is older and has been tested much more than the ARM version. Other kinds of x86_64 CPU are not supported (I don't think supporting other CPUs may pay off). Depending on the architecture, cpufetch choose certain files to be compiled. A summarized tree of the source code of cpufetch is shown below.
```
cpufetch/
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##### 1.1 Basics (x86_64)
In x86, __cpufetch works using the CPUID instruction__. It is called directly using assembly (see `src/x86/cpuid_asm.c`). To understand how CPUID works you may have a look at the [Useful documentation](https://github.com/Dr-Noob/cpufetch/blob/master/DOCUMENTATION_x86.md#useful-documentation) section (more precisely, Link 1).
In x86, __cpufetch works using the CPUID instruction__. It is called directly using assembly (see `src/x86/cpuid_asm.c`). To understand how CPUID works, see [DOCUMENTATION_X86.md](https://github.com/Dr-Noob/cpufetch/blob/master/doc/DOCUMENTATION_X86.md).
At the beginning of execution, cpufetch needs to know the max standard CPUID level and max CPUID extended level supported in the running CPU. We also need to know if the x86 CPU is Intel or AMD because some fetching depends on it. This information will be stored in:
At the beginning of execution, cpufetch needs to know the max standard CPUID level and max CPUID extended level supported in the running CPU. We also need to know if the x86 CPU is Intel or AMD because sometimes, the way to obtain the information depends on the manufacturer. This information will be stored in:
```
struct cpuInfo {
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};
```
To use any CPUID leaf, we always need to check that it is supported in the current CPU. cpufetch will always check if the leaf is supported in the current CPU, and will use a different workaround if the CPU is Intel or AMD, which leads us to the following section.
To use any CPUID leaf, cpufetch always need to check that it is supported in the current CPU.
##### 1.2 Basics (ARM)
In ARM, __cpufetch works using the MIDR register and Linux filesystem__. MIDR (Main ID Register) is fetched from `/proc/cpuinfo`. It allows the detection of the microarchitecture of the cores. Furthermore, Linux filesystem `/sys/devices/system/cpu/` is used to fetch the number of cores, and other information. This is the main reason to explain __why `cpufetch` only works on Linux kernel based systems.__
In ARM, __cpufetch works using the MIDR register and Linux filesystem__. MIDR (Main ID Register) is read from `/proc/cpuinfo`. It allows the detection of the microarchitecture of the cores. Furthermore, Linux filesystem `/sys/devices/system/cpu/` is used to fetch the number of cores, and other information. This is the main reason to explain __why `cpufetch` only works on Linux kernel based systems.__
##### 1.3 Documentation organization
The rest of the documentation is divided into x86 and ARM architectures, since each one need different implementations: