INES Mapper 065

 Here are Disch's original notes:  
 ========================
 =  Mapper 065          =
 ========================
 
 
 Example Games:
 --------------------------
 Daiku no Gen San 2
 Kaiketsu Yanchamaru 3
 Spartan X 2
 
 
 
 Registers:
 --------------------------
 
   $8000:  PRG Reg 0 (8k @ $8000)
   $A000:  PRG Reg 1 (8k @ $A000)
   $C000:  PRG Reg 2 (8k @ $C000)
 
   $B000-$B007:  CHR regs
 
   $9001:  [M... ....]  Mirroring
     0 = Vert
     1 = Horz
 
   $9003:  [E... ....]  IRQ Enable (0=disabled, 1=enabled)
   $9004:  [.... ....]  Reload IRQ counter
   $9005:  [IIII IIII]  High 8 bits of IRQ Reload value
   $9006:  [IIII IIII]  Low 8 bits of IRQ Reload value
 
 
 On Powerup:
 ---------------------------
 On powerup, it appears as though PRG regs are inited to specific values:
 
   $8000 = $00
   $A000 = $01
   $C000 = $FE
 
 Games do rely on this and will crash otherwise.
 
 
 PRG Setup:
 ---------------------------
 
       $8000   $A000   $C000   $E000  
     +-------+-------+-------+-------+
     | $8000 | $A000 | $C000 | { -1} |
     +-------+-------+-------+-------+
 
 
 CHR Setup:
 ---------------------------
 
       $0000   $0400   $0800   $0C00   $1000   $1400   $1800   $1C00 
     +-------+-------+-------+-------+-------+-------+-------+-------+
     | $B000 | $B001 | $B002 | $B003 | $B004 | $B005 | $B006 | $B007 |
     +-------+-------+-------+-------+-------+-------+-------+-------+
 
 
 
 IRQs:
 ---------------------------
 
 This mapper's IRQ system is very simple.  There's a 16-bit internal down counter which (when enabled),
 decrements by 1 every CPU cycle.  When the counter reaches 0, an IRQ is fired.  The counter stops at 0 -- it
 does not wrap and isn't automatically reloaded.
 
 Any write to $9003 or $9004 will acknowledge the pending IRQ.
 
 Any write to $9004 will copy the 16-bit reload value into the counter.
 
 $9006 and $9005 set the reload value, but do not have any effect on the actual counter.  Note that $9005 is
 the HIGH bits, not the low bits.