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 an hack to get 3 games working: Klax, Skull&Crossbones and Hard Drivin'.

• Address mask: $E001.
• Writing to the registers $E000 or $E001 acknowledges the IRQ.
• Register $C001 sets the IRQ clear flag to true (it's cleared at the next IRQ clock).

When the IRQ is clocked by CPU or scanline modes:

• If the IRQ counter++ == IRQ latch:
  • If IRQs are enabled, trigger an IRQ 2 CPU cycles later.
  • Set IRQ clear flag to true.
• If the IRQ clear flag is true:
  • IRQ counter is set to zero.
  • IRQ clear flag is set to false.

Notice!

• Skull&Crossbones has a glitched scanlined at the top of the scorebar, but NOT on the continue screen. Plus, the bottom line of the scorebar is NOT missing.
• Hard Drivin' works, but the title screen has 2 glitched scanlines.
• Klax is perfect, no problems.

--Zepper (talk) 17:12, 3 July 2017 (MDT)