Talk:RAMBO-1: Difference between revisions
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(→Alternate IRQ timing: Progress, Klax is off by 1 scanline only. All the others are perfect.) |
(→Alternate IRQ timing: No need of checking the irq_delay.) |
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| Line 28: | Line 28: | ||
writes to $E001: irq_enable=true; 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: | If irq_reload == true: | ||
irq_counter = irq_latch; | irq_counter = irq_latch; | ||
Revision as of 13:40, 6 August 2017
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)
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 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)
