Commits on Jul 6, 2024

1. Implement power saving primitive BANDGAP …

   As the board on the GW1N-1 chip becomes a rarity, its replacement is the
   Tangnano1k board with the GW1NZ-1 chip. This chip has a unique mechanism
   for turning off power to important things such as OSC, PLL, etc.
   
   Here we introduce a primitive that allows energy saving to be controlled
   dynamically.
   
   Nextpnr will add this primitive automatically if we do not use it
   explicitly - this is done to explicitly connect the control input since
   its default connection is neither VCC nor GND.
   
   BANDGAP only has an input, but does not have a fuse - it is on all the
   time. Of course, a reasonable question arises - what are these magic
   numbers in line 2258-2259 of gowin_pack.py?
   
   I really don’t want to consider these BANDGAP fuses precisely because
   this primitive is not configurable - and these bits are fuses that
   appear in the db.shortval[49]['unknown_75'] and
   db.logicinfo['unknown_74'] tables , which clearly describe something
   with decent configuration capabilities. This could be some kind of
   adjustable voltage stabilizer, which has an input MUX for control
   signals and one of the combinations connects BANDGAP.
   
   But this is not part of BANDGAP and I think I'll leave it as it is.
   
   Signed-off-by: YRabbit <rabbit@yrabbit.cyou>

   

   yrabbit committed Jul 6, 2024
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