frodo-wii/Docs/flavours.html
2009-01-13 18:46:42 +00:00

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