Talk:RAMBO-1: Difference between revisions

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m (→‎Alternate IRQ timing: Minor fixes.)
 
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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. --[[User:Drag|Drag]] 03:05, 9 November 2011 (UTC)
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. --[[User:Drag|Drag]] 03:05, 9 November 2011 (UTC)


== IRQ related - Hard Drivin' ==
== Alternate IRQ timing  ==


Suggested changes for the Mapper64 IRQ. It makes Hard Drivin' to work fine. No other games are affected with this change.
This is how to get 4 games working: Klax, Skull&Crossbones, Rolling Thunder and Hard Drivin'.
Every cycle on 6502 is either a read or a write cycle. So, you update the IRQ counter in the next CPU cycle:
*Address mask: $E001.
 
* '''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):
writes to $C000: irq_latch=data;
** Decrement IRQ counter by 1
writes to $C001: irq_reload=true; irq_mode=data&1;
** '''IF''' IRQ counter is now 0 '''AND''' IRQs are enabled
writes to $E000: irq_enable=false; IRQ acknowledge by CPU.
*** wait one M2 cycle, then trigger IRQ
writes to $E001: irq_enable=true; IRQ acknowledge by CPU.


Hard Drivin' works. --[[User:Zepper|Zepper]] ([[User talk:Zepper|talk]]) 17:57, 14 January 2014 (MST)
* When the IRQ is clocked by CPU or scanline modes:
 
== 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'''.
If irq_reload == true:
*Register $C001: IRQ_mode = value AND $01, IRQ_clear = '''true'''.
    irq_counter = irq_latch;
*Register $E000: IRQ_enable = '''false''', acknowledges IRQ.
    if irq_latch != 0
*Register $E001: IRQ_enable = '''true''', acknowledges IRQ.
      irq_counter |= 1;
    irq_reload=false;
Else if irq_counter == 0:
    irq_counter = irq_latch;
Else
    irq_counter--;
If irq_counter == 0 and irq_enable == true
    irq_delay=4 (IRQ will be fired 4 CPU cycles later)


== Alternate Method for RAMBO-1 IRQ ==


'''When the IRQ is clocked by CPU or scanline modes:'''
Nintendulator-NRS's source file /mappers/src/iNES/mapper064.cpp has an alternative implementation of the IRQ which allows it to work properly with all known games to use it: Klax, Skull & Crossbones and Hard Drivin'.
*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'''.

Latest revision as of 14:43, 9 July 2019

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)

Alternate IRQ timing

This is how to get 4 games working: Klax, Skull&Crossbones, Rolling Thunder and Hard Drivin'.

  • Address mask: $E001.
writes to $C000: irq_latch=data;
writes to $C001: irq_reload=true; irq_mode=data&1;
writes to $E000: irq_enable=false; IRQ acknowledge by CPU.
writes to $E001: irq_enable=true; IRQ acknowledge by CPU.
  • When the IRQ is clocked by CPU or scanline modes:
If irq_reload == true:
   irq_counter = irq_latch;
   if irq_latch != 0
      irq_counter |= 1;
   irq_reload=false;
Else if irq_counter == 0:
   irq_counter = irq_latch;
Else
   irq_counter--;
If irq_counter == 0 and irq_enable == true
   irq_delay=4 (IRQ will be fired 4 CPU cycles later)

Alternate Method for RAMBO-1 IRQ

Nintendulator-NRS's source file /mappers/src/iNES/mapper064.cpp has an alternative implementation of the IRQ which allows it to work properly with all known games to use it: Klax, Skull & Crossbones and Hard Drivin'.

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