Talk:RAMBO-1

As for the 2mb PRG, I'm not sure if the cart actually supports that much ROM, but the PRG registers apparently are 8 bits, and 8kb * $100 = 2048kb = 2mb. --Drag 03:05, 9 November 2011 (UTC)

IRQ related - Hard Drivin'

Suggested changes for the Mapper64 IRQ. It makes Hard Drivin' to work fine. No other games are affected with this change. Every cycle on 6502 is either a read or a write cycle. So, you update the IRQ counter in the next CPU cycle:

• IF $C001 was written to after previous clock
  • reload IRQ counter with IRQ Reload value PLUS ONE
• ELSE IF IRQ counter is 0
  • reload IRQ counter with IRQ Reload value

When the IRQ is clocked by the mapper (in scanline or cycle mode):

• • Decrement IRQ counter by 1
  • IF IRQ counter is now 0 AND IRQs are enabled
    • wait one M2 cycle, then trigger IRQ

Hard Drivin' works. --Zepper (talk) 17:57, 14 January 2014 (MST)

Alternate IRQ timing

This is how to get 3 games working: Klax, Skull&Crossbones and Hard Drivin'.

• Address mask: $E001.

• Register $C000: IRQ_latch = value AND $FE (last bit is NOT used), IRQ_clear = true.
• Register $C001: IRQ_mode = value AND $01, IRQ_clear = true.
• Register $E000: IRQ_enable = false, acknowledges IRQ.
• Register $E001: IRQ_enable = true, acknowledges IRQ.

When the IRQ is clocked by CPU or scanline modes:

• IF IRQ_counter++ == IRQ_latch:
  • IF IRQ_enable == true, wait 4 CPU cycles, then trigger an IRQ AND clear IRQ_counter.
• ELSE IF IRQ_clear == true:
  • Clear IRQ_counter and IRQ_clear = false.