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#ActualHodgman

Posted 24 September 2013 - 09:27 PM

I really wonder which CPU did that to you because I can't think of any like that.
Unless you mean the microcode in CPUs...

Yeah. The PPC's used in the PS3/360 have a shift-by-variable instruction, but it's microcoded. When the CPU hits one of them, it flushes the CPU pipeline, fetches the algorithm from ROM and runs it (while locking down shared CPU resources - e.g. dual issuing disabled), pretending that it was just a single instruction, before resuming normal operations.
 
It's nice that the new consoles are moving over to x86-land now and ditching these simple CPUs... though I do have a soft-spot for the SPE's; async memcpy ftw!


#1Hodgman

Posted 24 September 2013 - 09:21 PM


I really wonder which CPU did that to you because I can't think of any like that.
Unless you mean the microcode in CPUs...
Yeah. Yhe PPU (PS3/360 CPU) has a shift-by-variable instruction, but it's microcoded. When the CPU hits one of them, it flushes the CPU pipeline, fetches the algorithm from ROM and runs it (while locking down shared CPU resources - e.g. dual issuing disabled), pretending that it was just a single instruction, before resuming normal operations.

It's nice that the new consoles are moving over to x86-land now and ditching these simple CPUs... though I do have a soft-spot for the SPE's; async memcpy ftw!


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