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Discussion Starter #1 (Edited)
This key seems to be the solution for nearly every savin problem. But what does it really do? Is it depending on the system? I heard about people having a problem with saving in ePSXe and have to press F4 to get it work. I never had this problem on my System. So why there is this problem on some machines and on some not?
 

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Discussion Starter #3
I know that :)
But why it has to be pressed on some machines and on some not?
And wtf is this SIO IRQ doing?
 

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This is a really good question, I hope that some knowledgable emu-author types can post a good explanation. It's kind of like voodoo to me, if any games seem to be stalling while checking for memory cards, I hit F4 a couple of times, and they roll along.

I don't know what it does, but I know that it works.
 

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well I'm no emu author :( (...yet! :) )
but if you type SIO IRQ out, you get
Serial Input Output Interrupt ReQuest !!!
...you can figure out what that means for yourself ;)
 

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:sigh: Quite some time ago I'd posted my thoughts on this subject. Sadly, it seems that after a topic is inactive for awhile it gets trimmed, so I'll just have to type it again ;)

Please note that everything below is merely my speculation and could be (and probably is) wrong. My ideas are only the result of deductive reasoning, not scientific analysis:

At its most basic an IRQ (Interrupt ReQuest) is a method whereby functionality that's outside of a processor (the realtime clock or input devices, for example) can be allowed to gain the processor's time. Normally, if set to a given task, a processor will continue to execute the task until it reaches completion.

Imagine, if you will, that the processor is a clerical person in an office. The secretary, if left alone, will complete work that they have pending and, if no new work is assigned, will be left to idle. An IRQ can walk over to the clerical person and make a request. "Hi there! Could you take a look at this data, then do something with it?" The processor agrees and temporarily interrupts (hence the name) their previous work to see what the IRQ wants done.

The PSX's processor works in much the same way. If left to its own devices, it'd continuously loop through the code and nothing else. Like most other systems, the PSX also contains IRQs which cause the processor to temporarily perform other activiities. "The user has pressed the (X) button. Please update the screen as such, ok?" From the behavior I've observed, the SIO IRQ (which I assume stands for Sequential [or Serial, perhaps] Input/Output) controls the flow of information from the CD drive, memory cards and controllers.

Though I'm not certain, I'm willing to bet that in a real PSX the SIO IRQ is managed by the hardware or the PSX's firmware (software built into the hardware) and is polled (that is, checked) on a regular basis to see if there's new information awaiting the processor. Since a PC running an emulator lacks the hardware/firmware, a method was needed to manually make the system go out and check for new data. Hence, the need for 'Force SIO IRQ'; a feature which forces the system to re-read information from its external devices to check for updates.

Did that make any sense?
 

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In otherwords you request the emu to interupt the serial input/output function :p

I guess that means that pressing f4 you force the emu to stop checking serial devices (which I assume is the memory cards or the pads as these are the 2 areas that it fixes.)
 

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Discussion Starter #8 (Edited)
Ok, I understood the explanation of cluthu so far. That sounds really as it could be true :)
But my second question is still unanswered: Why on some systems and on some not?
 

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>Why on systems and on some not?
I'm not really aware of a certain game working on one configuration and not another. The cases where F4 is necessary seem pretty consistant. Do you have an example of this? Not that I'm doubting you, I'm just interested.

If such is the case, I'd suppose...timing issues? I really couldn't say.
 

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Discussion Starter #10 (Edited)
One game which requires in some cases pressing F4 is FF9. On my system it doesn't. But there were a lotta posts from people saying something about this problem.
 

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Spyro, Tony Hawk 1 & 2 need an F4 to get them going when the memory card is accessed the first time.

FF8, Gran Turismo 1 & 2 don't.

It's just curious why some games require it and others don't.
 
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