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   The Natural Philosopher  wrote:   
   > On 12/02/2024 22:17, Theo wrote:   
   > > druck  wrote:   
   > >> Luckily ARM doesn't have a management engine - yet!   
   > >   
   > > Arm doesn't have a management engine, because Arm (mostly) don't make   
   chips.   
   > > That's up to Qualcomm, Samsung or whoever.  You don't get a full datasheet   
   > > for what's in one of those.   
   > >   
   > > In the case of the original Pi, the Arm *is* the management engine.  It was   
   > > used for managing the GPU, which was the main function of the chip   
   originally.   
   > >   
   > > (well sorta, the original Broadcom chips didn't have an Arm in them)   
   > >   
   > > Theo   
   >   
   > Tell me more.  This is a corner of history I am only vaguely familiar   
   > with., Wasn't the original chip a failed set top box chip? Which is why   
   > it always had HDMI.....   
      
   https://en.wikipedia.org/wiki/Alphamosaic   
   https://en.wikipedia.org/wiki/VideoCore   
      
   The original Videocore graphics processor was designed by a Cambridge   
   company called Alphamosaic.  They were then bought by Broadcom in 2004.   
   They were used as GPUs that were in addition to the primary processor in the   
   system - eg in phones and media players (the 5th gen video iPod has a   
   Videocore 2, the Nokia 808 Pureview has a VC4 [*]).  There wasn't a CPU in   
   them at this point - all the software was running on the GPU, which would   
   communicate with the host CPU on a separate chip.  For example the video   
   iPod used an ARM7 CPU (PortalPlayer 5021C-TDF, dual ARM7 at about 75MHz).   
      
   When the Pi project was coming together, the folks at Cambridge Broadcom   
   were looking for a suitable chip.  The VC4 was already in production and did   
   roughly what they wanted but had no CPU, so the decision was made to modify   
   the existing chip.  The story goes that they raided their parts bin, found   
   an already-decade-old ARM1176 and slapped it in the VC4 - I heard the   
   timeline for this was a month.  The rest is history.   
      
   This is why the Pi Zero and 1 have the ancient ARMv6 CPU architecture, where   
   other vendors were already shipping ARMv7 CPUs (Cortex A8 and similar)   
   around 2007 or so.  And also why the boot process on Pi 1-3 is backwards   
   from what we're used to: they boot the GPU first and only later does the GPU   
   start up the Arm.  The GPU is the main processor in the system, the Arm is   
   a secondary processor.   
      
   Theo   
      
   [*] I believe the image processing stack for the 808 Pureview with its   
   then-massive sensor was written by Broadcom and/or Nokia Cambridge folks,   
   some of whom later worked on the Pi camera interface.   
      
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