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Forums > C64 Coding > Demos which load from tape ?

2004-09-04 11:38

yago

Registered: May 2002
Posts: 333

Demos which load from tape ?

After reading covert bitops rants about irq-tapeloader, i wondered if there are any Demos which load their next Part from Tape ?

Something like a castro ?

... 22 posts hidden. Click here to view all posts....

2004-09-04 13:35

yago

Registered: May 2002
Posts: 333

Maybe compo-rules for c64 should not only allow a c64,1541,yc-cable, but also a c64,1531,rf, so that "lowfi" demos must not be held in wild competetion..

2004-09-05 19:48

Cybernator
Account closed

Registered: Jun 2002
Posts: 154

The idea is to be able to load the next part while the previous is still working. But with tapeloaders, that's pretty much impossible (except with some very simple animations, but that's not the point).

2004-09-05 20:15

cmp
Account closed

Registered: Jun 2002
Posts: 4

I guess people would have a tendency to scratch their files if they were on vinyl...

2004-09-05 20:41

TDJ

Registered: Dec 2001
Posts: 1879

Quote: I guess people would have a tendency to scratch their files if they were on vinyl...

Very funny :)

2004-09-06 18:23

yago

Registered: May 2002
Posts: 333

Quote: The idea is to be able to load the next part while the previous is still working. But with tapeloaders, that's pretty much impossible (except with some very simple animations, but that's not the point).

Impossible ? I'll do it ;-)
If I understood your Article, while irq-loading from tape, there has to be always the same Amount of cycles for the "background stuff".
That would require some thoughts, but it should be possible to have effects running while irq-loading.
Whats a sane limit for the amount of rastertime while loading ?

However, last Time I programmed the 1531 is more then 15 Years ago, and even that was simple basic-turboload-interaction..

Another possibility is to connect the datasette-output to the sid-input, that should give some decent samples..

2004-09-06 21:46

Cybernator
Account closed

Registered: Jun 2002
Posts: 154

> Impossible ?

Read again, depends on what you are doing. Effects which require
precise timing are impossible, and even Crossbow will have to humbly
agree. :) (ok, they are possible if hellish flickering is allowed :))

> I'll do it ;-)

I'll have to admit, it's always nice to see something never
done before. :)

> If I understood your Article, while irq-loading from
> tape, there has to be always the same Amount of cycles
> for the "background stuff".

I assume "background stuff" = the effects. Well, no actually.
'The same amount of cycles' thingy was in the saver. Since you
are not using a timer when saving, you have to be careful about
how many cycles have passed, and record the pulse at the correct
moment. It would've been simple if there weren't for the different
branches.

> That would require some thoughts, but it should be
> possible to have effects running while irq-loading.
> Whats a sane limit for the amount of rastertime while
> loading ?

Let's clear some things first. With diskloaders, all the effects
go into an IRQ, so they have higher priority over the loader.
In fact, the loader has the lowest priority since the protocol
is completely asynchronous (thank the 1541's CPU :))

With tapeloaders, it's vice-versa. The loader goes into an IRQ, giving
it the highest priority, which is pretty logical. With diskloaders,
the 1541 takes care of all timing-critical parts (the low-level
disk surface access). But since the tape lacks a CPU, the 6510 has
to take over and do all the timing critical parts. So loading goes into an
IRQ.. Now guess what would happen if you do VSP. No, simply guess
what would happen if you want to display some rasterbars.
Should you somehow make the rasterbars have higher priority than
the loader, you'll always end up with ?LOAD ERROR. Ah, those were
the times. :)

So back to your question, there's no need to worry about a rastertime
limit. :)

There's a possibility that you make the short pulse at least one frame
long, and the long one about two frames long, so you can have the effects in IRQ
and loading outside the IRQ (you only have to make sure that the loader will NEVER
miss a pulse). But one probably couldn't express the slowness of such a record, so
that has no practical purposes.

> However, last Time I programmed the 1531 is more then
> 15 Years ago, and even that was simple basic-turboload-interaction..

That's the hardest part, getting to work with it. After you make your
first Turbo250 clone, IRQ loading should be a breeze. :)

> Another possibility is to connect the datasette-output
> to the sid-input, that should give some decent samples..

Yeah, 1-bit samples. :) Perhaps you've tried Digitizer Datassette?

Oh, almost forgot: tape loading is hellish slow. A Turbo250 record
(which is much faster than IRQ-loader record - don't ask me how much, though :)),
is as fast (or should I say as slow) as a 1541 with the original kernel routines.

Hopefully I haven't destroyed your enthusiasm.
NO! Don't throw your Datassette! :P At least the tape has higher capacity than the
disk, making it a perfect backup storage. I wonder how many disks would I need
to transfer the games from my ca. 200 tapes. :)

2004-09-06 23:15

yago

Registered: May 2002
Posts: 333

Thanks for the clarification concerning disk/tape loading.
Hmm.. no raster effects.. :-(

You misunderstood my datasette-sid idea.
The datasette must be modified, so that it has a headphone-connector. With this, one can not only control the loading, but also put audio-cassettes into, and listen to music.

And this output shall not be digitized, just given to audio-in, so that the sid can filter it.

Surely this is cheating, because hardware-mods are required!

PS: I dont throw datasettes, just Disks and Printers!

2004-09-07 07:46

Hoogo

Registered: Jun 2002
Posts: 105

You surely can load from tape while having rasters or things like that. Pulses from the tape are shown in the Irq-Register $dc0d.
-Usual Turbotapes loop and watch $dc0d. The number of loops needed tells about the lenght of the pulse on tape.
-Allowing these Irq's is neat. Then you don't count in a loop, then you read the timers.
-But you can also check the register regulary, i.e. every 63 or 126 cycles, and put that into the raster-routine.

And the speed of the tape-loaders is limited by the quality of the tapes. When connecting a PC-Soundcard or anything else to the usual port, you can have much faster loaders. But I think that would be called cheating :-)

2004-09-07 15:52

algorithm

Registered: May 2002
Posts: 707

As a past C64 Coder without a floppy drive. my last multipart demo's consisted of a tape irq loader which would display a part while loading the next. The main restriction was lack of solid raster timing, altough music, split screen etc was possible (I think sprites on screen caused load errors?)

2004-09-07 17:19

Graham
Account closed

Registered: Dec 2002
Posts: 990

@Hoogo:

actually it's vice versa. samples are not very suitable for a storage which is based on variable signal lengths. this is way more accurate on an analogue tape than on a 44100 or even 22050 Hz sample... think of it: 44100 Hz = 22 cycles resolution. that's why very tight loaders do not work when converting them from TAP files to real tapes via audio out.

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