Date   : Mon, 08 Aug 2005 21:39:24 +0200
From   : John Kortink <kortink@...>
Subject: Re: GoMMC supports tapes

On Mon,  8 Aug 2005 13:03:32 +0000 (GMT), "Thomas Harte" wrote:

>> The OS patch ensures that the BBC's tape filing system
>> gets its input from a (selectable) tape image on the MMC
>> (via GoMMC) instead of an actual cassette tape (via the
>> cassette interface). There are no further differences.
>> The same old procedures to load the 'tape' are used
>> (*TAPE, then CHAIN"" or *RUN).
>
>Can I ask how you've hooked this in? I have for a long time
>wanted to dramatically improve the 'fast tape hack' loading
>in ElectrEm and have been looking for the absolute slightest
>internal piece of ROM code that can be modified. At the minute
>a blitz approach of replacing OSFILE, etc, is used and I seem
>to have never ending problems fooling some of the more
>sophisticated copy protection schemes.

I currently put double-NOP at F58D, F77E, F79A and FAE0,
catch service call 14, and serve it if the tape filing
system is selected (?&247 == 0). I.e. I (ab)use the fact
that the tape and ROM filing system are intertwined.

Under emulation I suppose you could easily feed the system
'tape bytes' at the same hook points.

>> This introduces a way to quickly and easily run fully
>> original tapes on the BBC, without the need for feeding
>> audio to the machine.
>> 
>> Tapes load quicker too (for example, Firetrack loads in
>> about 40 seconds total via GoMMC, against 5+ minutes via
>> the regular way).
>
>Some games seem simply not to function if loaded 'quickly',
>presumably a copy protection mechanism that counts time is
>incorporated. So if possible, an option to load at normal
>speed might be desirable.

Yep. I've arranged that in GoMMC by a 'slow down' option.


John Kortink


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