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Posted By

TommoH
on 2025-01-15
21:52:39

Re: What format is data on a tape?

Yes! Fantastic!

So: (i) I was off above in forgetting that numbers in a TAP are divided by 8; but, also (ii) the Plus 4 does indeed differ in tape format from the other Commodores — pulse lengths are substantially altered.

Thanks!

Posted By

Csabo
on 2025-01-15
08:06:46

Re: What format is data on a tape?

Does this topic have the info you need? There are many other topics in the encyclopedia that describe the details of various turbos (thanks to Ulysses777!).

Posted By

TommoH
on 2025-01-15
06:28:28

Re: What format is data on a tape?

But surely it has to start with a Kernal-encoded loader, which would be amongst the short half-waves I saw near the start of the file?

Is that part in the same encoding as the Vic-20 and C64 or is the Plus 4 doing something unique? Between the bad lines and the polled input level it'd be understandable.

Posted By

gerliczer
on 2025-01-14
22:57:44

Re: What format is data on a tape?

That game is loaded with an auto-starting fast-loader. So, it is not the native KERNAL tape format. Judging by the loader effect, it is probably a Her-Turbo tape. There is some information on that here in the encyclopedia. The article is titled "Zifra / Her Turbo Tape Format."

Posted By

TommoH
on 2025-01-14
22:39:58

What format is data on a tape?

I am of course aware of the standard Commodore format, as briefly summarised in places like The Complete Commodore Inner Space Anthology (bottom of Page 97), which at the physical layer involves a long wave length that is 262µs per pole, a short that is 182µs and a mark that is 342µs. So it's close to an average of 560 bytes/second in purely physical terms.

However if I look at — arbitrarily — the Mad Rally .tap file from this site, which seems to be encoded as a bunch of individual pole lengths at the half-speed CPU clock rate then I see the lead-in section is mostly numbers around $1C i.e. 28 cycles @ ~890kHz or ~31µs. Ditto if I scroll down to the code area then I see pole lengths like $0F and $22, i.e. ~17µs and ~25µs. But that's an improbable almost 6000 bytes/second if each bits is still only one single full wave.

That compares to other micros tending to be around the 1200 mark, sometimes with an unreliable high-speed option of 2400 bytes/second or so.

That said: if I interpret the TAP file as above, i.e. that an in-file length of $22 means 34/886,722 ths of a second on a PAL machine, then an emulated Plus 4 can load the file.

I do not think I've misunderstood the standard Commodore tape format because if I serialise a PRG file back to a tape wave stream in standard Commodore form and feed it to an emulated Vic-20 then it loads.

So, which is it?

Does the Plus 4 have a unique tape data encoding? If so, where can I find it?

Or am I suffering a misapprehension and/or an error in my workings, or some other failure of comprehension?

I'm guessing the latter, but the fact that my emulated Commodore 16 loads TAP files with that interpretation is somewhat throwing me. I'm obviously screwing up somewhere.