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Atari demoscene BBS
| Re: Sans sujet |
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Posted by: ggn
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Jun,06.2016-21:01
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Ok, I'll try to give a short (and hopefully accurate) explanation of what happens when you press reset on the ST:
- First of all the reset button is more or less wired to the RESET pin of the 68000. So hitting the button will simply reset the CPU but not the peripherals (to the CPU even memory is a peripheral of sorts). Since the RAM and its controller is still getting power when you press reset, its contents are kept intact. In fact TOS or whatever boots is responsible for clearing the memory if needed.
- Very very early into the TOS boot code (it barely resets some peripherals and checks if there's a diagnostic cart installed), a certain memory location is checked ($426). If that contains the magic value $31415926 (yeah, you know, geeks write O/Ses :)) then a 2nd memory location is accessed ($42a). The second memory location contains the address of where to execute code, and it proceeds doing that immediately.
(BTW, TOS is full of magic numbers internally but this one is probably the most "fun")
- Now, the machine isn't fully brought up at this point so it's at our mercy. The memory is untouched so if we have placed code somewhere, it is not overwritten by anything. So we can safely execute demo code!
- A small piece of trivia here is that all STs reset to 60Hz! Later in the boot process TOS decides whether to set 50 or 60Hz, but since the startup code runs for a few milliseconds it's not really noticeable by anyone, but it does mean that the reset demos need to set frequency to 50Hz by hand :).
Well, I can't think of anything relevant here. If I do, I might follow up this post!
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[All messages in this thread] [Start new thread]
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Topic
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Posted by
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Date
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Best hidden / reset screens
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S_t_s
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Jun,06.2016-11:33
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Re: Best hidden / reset screens
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ggn
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Jun,06.2016-12:27
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Re: Best hidden / reset screens
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evil
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Jun,06.2016-16:02
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Sans sujet
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s_t_s
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Jun,06.2016-17:52
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Re: Sans sujet
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ggn
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Jun,06.2016-21:01
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Re: Sans sujet
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s_t_s
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Jun,07.2016-08:47
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Re: Best hidden / reset screens
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grazey/phf
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Jun,06.2016-18:12
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Re: Best hidden / reset screens
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s_t_s
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Jun,07.2016-08:49
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Re: Best hidden / reset screens
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Orion_
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Jun,08.2016-19:27
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Re: Best hidden / reset screens
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s_t_s
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Jun,10.2016-16:51
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Re: Best hidden / reset screens
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gwEm
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Jun,12.2016-13:05
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Re: Best hidden / reset screens
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Gwem
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Jun,12.2016-13:09
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Re: Best hidden / reset screens
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Leonard
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Jun,12.2016-23:57
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Re: Best hidden / reset screens
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s_t_s
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Jun,14.2016-09:09
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Re: Best hidden / reset screens
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PeyloW
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Jun,16.2016-23:11
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What's the anti-troll code?
That's your personal code to be able to add comments and messages on the dhs.nu site.
Don't have a code or forgot it? Fix it here.
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