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[[File:PSP CXD2962GG.jpg|thumb|PSP CXD2962GG]]
Tachyon is the codename of the PSP main CPU SoC IC. It is a Sony custom-made LSI which holds the main CPU (Allegrex), the VFPU coprocessor, the Media Engine CPU and its embedded DRAM, the Graphics Engine, the AVC decoder, the Virtual Mobile Engine DSP, the [[Kirk]] and [[Spock]] crypto engines, and the 4KB embedded mask ROM which holds the [[PRE-IPL|iplloader]] and routines to boot into service mode. Tachyon has one primary CPU core which is responsible for running the XMB and games, and a second CPU core (Media Engine) which implements the audio and video decoding functionality of the PSP.


<b>Tachyon</b> is the codename of the PSP main CPU SoC IC. It is a Sony custom-made LSI which holds the main CPU (Allegrex), the VFPU coprocessor, the Media Engine CPU and its embedded DRAM, the Graphics Engine, the AVC decoder, the Virtual Mobile Engine DSP, the [[Kirk]] and [[Spock]] crypto engines, and the 4KB embedded mask ROM which holds the [[iplloader]] and routines to boot into service mode.
[[File:PSP CXD2962GG.jpg|thumb|left|PSP CXD2962GG]]<br>
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Tachyon has one primary CPU core which is responsible for running the [[XMB]] and games, and a second CPU core (<i>[[Media Engine]]</i>) which implements the audio and video decoding functionality of the PSP.
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== Main Core "SC" ==
== Main Core "SC" ==


See [[Allegrex]].
The PSP's CPU is a dual core 32-bit Little Endian MIPS based on the R4000 design with a few custom instructions.


== Media Engine ==
Both CPU cores have their own 16 KiB Instruction and 16KiB Data caches. The main CPU has an internal 16 KiB of scratchpad RAM that is accessed directly without going through the system bus.


See [[Media Engine]].
The main CPU has three coprocessors:
*COP0 - general system control
*COP1 - 32-bit Floating Point Unit
*COP2 - Vector Floating Point Unit (up to 3.2 GFLOPS)


== Virtual Mobile Engine ==
The CPU defaults to 222MHz, but can be configured to run from 1-333 MHz.


See [[Virtual Mobile Engine]].
The CPU cores are connected to main memory and other peripherals like the Graphics Engine through a system bus that is limited to 1/2 of the CPU's configured clock speed.


== Graphics Engine ==
== Media Engine ==


: <i>See main article: <b>[[Graphics]]</b></i>
The Media Engine ("ME") is a second MIPS based CPU core that was not directly accessible by licensed developers. Instead, Sony runs code on the ME to facilitate decoding audio and video assets, along with the help of more specialized hardware like the Virtual Mobile Engine and "AVC".


== Memory mapping ==
The ME runs at the same clock frequency as the main CPU core.


This memory mapping is shared by the SC, the GE & the ME, except the VRAM which is accessible only by the SC and the GE.
The ME has two co-processors:
*COP0 - general system control
*COP1 - 32-bit Floating Point Unit


{| class="wikitable"
== Graphics Engine ==
|-
! Start !! End !! Size !! Description
|-
| 0x00010000 || 0x00013FFF || 0x00004000 (<i>16KiB</i>) || Allegrex Scratchpad
|-
| 0x04000000 || 0x041FFFFF || 0x00200000 (<i>2MiB</i>)  || Graphics Engine VRAM
|-
| 0x08000000 || 0x087FFFFF || 0x00800000 (<i>8MiB</i>)  || Allegrex Kernel memory (RAM)
|-
| 0x08800000 || 0x09FFFFFF || 0x01800000 (<i>24MiB</i>) || Allegrex User memory (RAM)
|-
| 0x1C000000 || ?          || ?                        || Hardware registers
|-
| 0x1FC00000 || 0x1FDFFFFF || 0x00200000                || MIPS Reset Vector
|-
| 0x1FE00000 || ?          || ?                        || Hardware registers
|-
|}


See [[Hardware Registers]] for details about the hardware registers.
== Virtual Mobile Engine ==
 
Access can be cached & privileged or not by changing the first 4 bits (<i>31-28 bits</i>) of the address using this virtual memory mapping:
{| class="wikitable"
|-
! Address !! Name !! Is it cached? !! Permission || Description
|-
| 0x<b>0</b>0000000 || KU0  || Cached  || User/Supervisor/Kernel || Main memory
|-
| 0x<b>4</b>0000000 || KU1  || Uncached || User/Supervisor/Kernel || Often used for VRAM
|-
| 0x<b>8</b>0000000 || K0    || Cached  || Kernel || Main kernel memory
|-
| 0x<b>A</b>0000000 || K1    || Uncached || Kernel || Mainly used for hardware registers
|-
| 0x<b>C</b>0000000 || K2/KS || Cached  || Supervisor/Kernel || Usage unknown/unconfirmed
|-
| 0x<b>E</b>0000000 || K3    || Cached  || Kernel || Usage unknown/unconfirmed
|-
|}
 
== PSP-1000 VFPU bug ==
 
PSP-1000 CPU has broken <code>ulv.q</code> instruction, that causes FPU registers corruption.


You can see more about it [https://sites.google.com/a/davidgf.es/davidgf-net/home/psp-dev/vfpu-test?tmpl=%2Fsystem%2Fapp%2Ftemplates%2Fprint%2F here].
The VME appears to be one half of Sony's "Virtual Mobile Engine Concept 2" where a CPU would take care of "lightweight control tasks" and reconfigurable hardware logic (the VME) would do all of the "heavy work in a power efficient manner". See [https://www.yumpu.com/en/document/read/10961029/virtual-mobile-enginetm-vme-sony Virtual Mobile Engine - LSI that "Changes its Spots"].


== Versions ==  
== Versions ==  
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* https://www.zdnet.com/article/sony-reveals-some-specs-for-psp-handheld/ (2004)
* https://www.zdnet.com/article/sony-reveals-some-specs-for-psp-handheld/ (2004)


* https://www.extremetech.com/extreme/56942-sony-details-psp-chip-specs
https://www.extremetech.com/extreme/56942-sony-details-psp-chip-specs


* https://www.copetti.org/writings/consoles/playstation-portable/
https://www.copetti.org/writings/consoles/playstation-portable/
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