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59 lines
2.0 KiB
HTML
59 lines
2.0 KiB
HTML
<HTML>
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<HEAD>
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<TITLE>Frodo and Frodo SC</TITLE>
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</HEAD>
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<BODY>
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<H1>Frodo and Frodo SC</H1>
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<HR>
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Frodo comes in two 'flavours' that allow you to decide between speed
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and accuracy of the emulation.
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<H2>The line-based emulation 'Frodo'</H2>
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<B>Frodo</B> is a line-based emulation, i.e. the activities that happen
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in parallel during one video line in the real C64 are emulated one after
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the other for the different chips. This offers a reasonable degree of
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precision of the emulation at a decent speed. There are some things that
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cannot be emulated with this technique, but it works fine with about
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80% of all C64 programs and it is also the faster of the two Frodo
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versions.
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<HR>
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<H2>The single-cycle emulation 'Frodo SC'</H2>
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<B>Frodo SC</B> is a special version of Frodo that doesn't work with a
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line-based emulation but instead with a cycle-based one. That means that
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the emulator switches between 6510 and VIC in every emulated ø2 clock
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phase. By doing this, Frodo SC achieves an extreme precision (nearly all
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$d011 and $d016 effects can be emulated), but at the expense of speed.
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In the settings options, Frodo SC differs from Frodo in only a few points:
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<UL>
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<LI>The "Cycles per line" settings are not available as the timing of Frodo SC is hardcoded
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<LI>The "Clear CIA IRC on write" hack is not necessary
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</UL>
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Apart from that, Frodo SC is operated in the same way as Frodo and also
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uses the same settings. Frodo SC has only a few incompatibilities to a
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real C64:
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<UL>
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<LI>On the left and right side of the screen, sprites are not clipped but blanked out
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<LI>Sprite collisions are only detected within the visible screen area (excluding borders)
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<LI>The sprite data fetch ignores the state of BA
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<LI>On BA low and AEC high, the VIC always reads $f in D8-D11
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<LI>Color register modifications are visible 7 pixels too late
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<LI>The TOD clock should not be stopped on a read access, but be latched
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<LI>The SDR interrupt is faked
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<LI>Some small incompatibilities with the CIA timers
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<LI>The readable SID registers are not emulated correctly
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</UL>
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</BODY>
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</HTML>
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