Re: [hatari-devel] 68040/060 MMU bug fix

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 29/12/2023 à 15:25, Andreas Grabher a écrit :

> The complexity of interrupt code in WinUAE is very high due to 
> handling lots of different CPUs and emulation modes. This increases 
> the chance to mess things up unintentionally. There is interrupt code 
> in lots of places using SPCFLAG_INT, SPCFLAG_DOINT, regs.ipl[0], 
> regs,ipl[1], regs.ipl[2], ipl_pin, ipl_pin_p, do_interrupt(), 
> check_interrupt(), ipl_fetch_xxx(), doint(), checkint(), 
> m68k_interrupt_delay, m68k_accurate_ipl … just to name a few.
>
> Is there a chance this will be cleaned up a bit which would also 
> improve performance?

Hi

toni will certainly elaborate more on this, but in the case of the 68000 
having cycle accurate emulation of the micro code unfortunately imply to 
have sometimes a lot of variables just to emulate a very particular 
behaviour.

for example, deciding which value of the hardware ipl pins is sampled to 
decide at which stage an opcode will be interrupted in case of a change 
in IPL is really tricky. That's why  the ipl[] array is needed because 
you need to keep an history of the IPL values during the previous cycle 
as well as at what cycles the IPL changed

This variable are also there to help improving perfomance : if you 
disable m68k_accurate_ipl or m68k_interrupt_delay you will have a less 
cycle accurate but slightly faster emulation , which can good enough for 
68030 (which is not cycle accurate emulated anyway)

But I agree dealing with all those variables and function can be 
difficult when you're trying to follow the code :)

Nicolas