Frodo4/Docs/flavours.html

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<HEAD>
<TITLE>Frodo and Frodo SC</TITLE>
</HEAD>
<BODY>

<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
</UL>

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</HTML>
Revision:	1.2
Committed:	2003-07-09T13:59:33Z (21 years, 4 months ago) by cebix
Content type:	text/html
Branch:	MAIN
CVS Tags:	VERSION_4_2
Changes since 1.1:	+5 -23 lines
Log Message:	no more Frodo PC
#	User	Rev	Content
1	cebix	1.1	<HTML>
2			<HEAD>
3	cebix	1.2	<TITLE>Frodo and Frodo SC</TITLE>
4	cebix	1.1	</HEAD>
5			<BODY>
6
7	cebix	1.2	<H1>Frodo and Frodo SC</H1>
8	cebix	1.1
9			<HR>
10
11	cebix	1.2	Frodo comes in two 'flavours' that allow you to decide between speed
12	cebix	1.1	and accuracy of the emulation.
13
14			<H2>The line-based emulation 'Frodo'</H2>
15
16			<B>Frodo</B> is a line-based emulation, i.e. the activities that happen
17			in parallel during one video line in the real C64 are emulated one after
18			the other for the different chips. This offers a reasonable degree of
19			precision of the emulation at a decent speed. There are some things that
20			cannot be emulated with this technique, but it works fine with about
21	cebix	1.2	80% of all C64 programs and it is also the faster of the two Frodo
22	cebix	1.1	versions.
23
24			<HR>
25
26			<H2>The single-cycle emulation 'Frodo SC'</H2>
27
28			<B>Frodo SC</B> is a special version of Frodo that doesn't work with a
29			line-based emulation but instead with a cycle-based one. That means that
30			the emulator switches between 6510 and VIC in every emulated ø2 clock
31			phase. By doing this, Frodo SC achieves an extreme precision (nearly all
32			$d011 and $d016 effects can be emulated), but at the expense of speed.
33
34	cebix	1.2	In the settings options, Frodo SC differs from Frodo in only a few points:
35	cebix	1.1
36			<UL>
37			<LI>The "Cycles per line" settings are not available as the timing of Frodo SC is hardcoded
38			<LI>The "Clear CIA IRC on write" hack is not necessary
39			</UL>
40
41			Apart from that, Frodo SC is operated in the same way as Frodo and also
42			uses the same settings. Frodo SC has only a few incompatibilities to a
43			real C64:
44
45			<UL>
46			<LI>On the left and right side of the screen, sprites are not clipped but blanked out
47			<LI>Sprite collisions are only detected within the visible screen area (excluding borders)
48			<LI>The sprite data fetch ignores the state of BA
49			<LI>On BA low and AEC high, the VIC always reads $f in D8-D11
50			<LI>Color register modifications are visible 7 pixels too late
51			<LI>The TOD clock should not be stopped on a read access, but be latched
52			<LI>The SDR interrupt is faked
53			<LI>Some small incompatibilities with the CIA timers
54			<LI>The readable SID registers are not emulated correctly
55			</UL>
56
57			</BODY>
58			</HTML>