| 1 |
cebix |
1.1 |
<HTML> |
| 2 |
|
|
<HEAD> |
| 3 |
|
|
<TITLE>Frodo, Frodo PC and Frodo SC</TITLE> |
| 4 |
|
|
</HEAD> |
| 5 |
|
|
<BODY> |
| 6 |
|
|
|
| 7 |
|
|
<H1>Frodo, Frodo PC and Frodo SC</H1> |
| 8 |
|
|
|
| 9 |
|
|
<HR> |
| 10 |
|
|
|
| 11 |
|
|
Frodo comes in three 'flavours' that allow you to decide between speed |
| 12 |
|
|
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 |
|
|
80% of all C64 programs and it is also the fastest of the three Frodo |
| 22 |
|
|
versions. |
| 23 |
|
|
|
| 24 |
|
|
<HR> |
| 25 |
|
|
|
| 26 |
|
|
<H2>The improved line-based emulation 'Frodo PC'</H2> |
| 27 |
|
|
|
| 28 |
|
|
<B>Frodo PC</B> is also a line-based emulation but it has some improvements |
| 29 |
|
|
over the standard Frodo: |
| 30 |
|
|
|
| 31 |
|
|
<UL> |
| 32 |
|
|
<LI>Code in chip registers can be executed |
| 33 |
|
|
<LI>Correct calculation of 6510 instruction cycles |
| 34 |
|
|
<LI>More precise CIA emulation |
| 35 |
|
|
</UL> |
| 36 |
|
|
|
| 37 |
|
|
Programs that don't work on the standard Frodo or that produce an |
| 38 |
|
|
"Illegal jump to I/O space" message might work with Frodo PC. However, |
| 39 |
|
|
Frodo PC is a bit slower. |
| 40 |
|
|
|
| 41 |
|
|
<HR> |
| 42 |
|
|
|
| 43 |
|
|
<H2>The single-cycle emulation 'Frodo SC'</H2> |
| 44 |
|
|
|
| 45 |
|
|
<B>Frodo SC</B> is a special version of Frodo that doesn't work with a |
| 46 |
|
|
line-based emulation but instead with a cycle-based one. That means that |
| 47 |
|
|
the emulator switches between 6510 and VIC in every emulated ø2 clock |
| 48 |
|
|
phase. By doing this, Frodo SC achieves an extreme precision (nearly all |
| 49 |
|
|
$d011 and $d016 effects can be emulated), but at the expense of speed. |
| 50 |
|
|
|
| 51 |
|
|
In the settings options, Frodo SC differs from Frodo/Frodo PC in only |
| 52 |
|
|
a few points: |
| 53 |
|
|
|
| 54 |
|
|
<UL> |
| 55 |
|
|
<LI>The "Cycles per line" settings are not available as the timing of Frodo SC is hardcoded |
| 56 |
|
|
<LI>The "Clear CIA IRC on write" hack is not necessary |
| 57 |
|
|
</UL> |
| 58 |
|
|
|
| 59 |
|
|
Apart from that, Frodo SC is operated in the same way as Frodo and also |
| 60 |
|
|
uses the same settings. Frodo SC has only a few incompatibilities to a |
| 61 |
|
|
real C64: |
| 62 |
|
|
|
| 63 |
|
|
<UL> |
| 64 |
|
|
<LI>On the left and right side of the screen, sprites are not clipped but blanked out |
| 65 |
|
|
<LI>Sprite collisions are only detected within the visible screen area (excluding borders) |
| 66 |
|
|
<LI>The sprite data fetch ignores the state of BA |
| 67 |
|
|
<LI>On BA low and AEC high, the VIC always reads $f in D8-D11 |
| 68 |
|
|
<LI>Color register modifications are visible 7 pixels too late |
| 69 |
|
|
<LI>The TOD clock should not be stopped on a read access, but be latched |
| 70 |
|
|
<LI>The SDR interrupt is faked |
| 71 |
|
|
<LI>Some small incompatibilities with the CIA timers |
| 72 |
|
|
<LI>The readable SID registers are not emulated correctly |
| 73 |
|
|
</UL> |
| 74 |
|
|
|
| 75 |
|
|
</BODY> |
| 76 |
|
|
</HTML> |
