Forum comments in chronological order

Anonymous
Sat 11-Feb-2017 14:13

https://youtu.be/Tr30Qubu_V4

Whose version is this?

Anonymous
Sun 12-Feb-2017 05:50

That was the "summery"; you are an insult to lazy people everywhere.

But you have redeemed yourself with a great toast: To long, jesus christ! >clink!<

Anonymous
Wed 15-Feb-2017 01:26

you are genius !!!!!

Anonymous
Wed 15-Feb-2017 12:04

I've just compiled this and got it working unmodified on MacOS 10.12.3. It also works on Raspbian, which is where I usually play.

Thanks for the post!

Anonymous
Wed 15-Feb-2017 16:46

Varicella (shown in the screenshot at the top of the page) is a z8 game. That doesn't automatically mean that all z8 games work.

-- Fredrik

Anonymous
Wed 15-Feb-2017 16:56

Det är troligen betydligt mer än fonten som skapar problem. Inmatning och utmatning av svenska tecken, användandet av en alternativ alfabetstabell, och tidsstyrd inmatning är exempel på områden som måste funka för att köra Stugan, och som krånglar även i många ganska mogna speltolkar.

/Fredrik (som skapade Z-kodsversionen av Stugan)

Anonymous
Sat 18-Feb-2017 18:18

Hi,
Please could you explain why you can say this:
"the phase of the colour carrier with respect to the dotclock. The latter is assigned randomly at power-on".
I believe the MOS-8701 works with fixed delays to generate the dot clock, so it should come up with always the same phase with respect to the color clock.
On the boards with no MOS-8701, there's a classic PLL circuit that should come up with always the same phase relationship too.
What am I missing? Thanks (iz8dwf at amsat dot org)

Anonymous
Sat 18-Feb-2017 19:46

Thank you Linus. Really helped me understand this stuff.

lft
Linus Åkesson
Thu 23-Feb-2017 17:16

Hi!

The MOS-8701 produces a 7.88 MHz dotclock and a 4.43 MHz colour carrier from the same internal signal. Their ratio is exactly 16:9, which means that 16 hi-res pixels on the screen correspond to nine complete cycles of the colour signal.

It follows that for each hi-res pixel, the phase of the colour carrier is advanced by 9/16 revolutions, which is 202.5 degrees. If it starts at 0 degrees, then after 8 hi-res pixels it will be at 180 degrees. Hence the familiar red/green vertical banding that repeats after 16 pixels; red and green are 180 degrees apart in YUV.

Now, at which pixel is the colour carrier at 0 degrees?

This depends on the timing relationship between the 8701 and the VIC chip. The 8701 has a reset pin, but it doesn't seem to be connected in the C64. The VIC doesn't even have a reset pin.

So, during power-on, there will be a brief period before the 8701 is outputting a stable signal, and during this period the VIC state machine may or may not respond properly. Meanwhile, the internal clock-divide counters of the 8701 might not even start from zero.

That is where the random assignment happens.

lft
Linus Åkesson
Thu 23-Feb-2017 17:18

Yes, and often several bytes at the same time.

Banking doesn't affect anything, I'm afraid, because the Row Select procedure (LSB) is carried out regardless of what the MSB will be. The corruption happens inside the RAM chips themselves.

Anonymous
Fri 24-Feb-2017 09:43

I'm unsure whether to laugh at this article, or cringe from sheer fremdschämen on its author's behalf. Currently sitting halfway in abject disbelief.

Rather than attempt a sane response, I'll simply recommend you poke through nested Groff macros or the magic-data tables of the venerable file(1) program (ftp://ftp.astron.com/pub/file/file-5.30.tar.gz, under magic/Magdir). If you can dig through those without admitting highlighting plays a critical role in legibility, you're kidding yourself; but you're not kidding every reader shaking their head over this tripe.

Anonymous
Sat 25-Feb-2017 03:19

Hej, just noticed that the page is broken if you get here via HTTPS; not all browsers allow you to embed HTTP frames in an HTTPS page these days. Should be easy to fix.

Anonymous
Sun 26-Feb-2017 20:25

Actually, from the C64 schematics (and from what I can see from a scope) the colour clock output is 4 x 4.433619 MHz which is the crystal frequency, and this signal goes to the VIC-II.
The colour carrier is obtained internally on the VIC-II, but what you say of course doesn't depend from where the 4.433 MHz signal is
generated.


this could be true.

The discussion is very interesting to me since eliminating a precise phase offset between the two clocks (as long as it's constant after each power up) could allow to make a very cheap 8701 replacement.