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Message: 5880

Author: jgh@arcade.demon.co.uk

Date: 26/07/2006

Subject: Re: Finding unused addresses

 

Message-ID: < e2gnlg+6kfj@... >

andrewbroad wrote:

This is an erratum to Message 5792; changes are embedded below.

------------------------
Finding unused addresses
------------------------
In the unpatched game-engines, the free space is as follows:

JSW48
-----

&8451-&8453 (3 bytes) contain the left-over string "AIR" which is
not used by the game engine.

&858B-&85CA (64 bytes) contain the password entry prompts, which
are usually unused.

* #869F-87C9 (#12B bytes) contain the colour-code routine, which is
usually bypassed.

Could I suggest to the JSW patching community the following
convention:

If &8451-&8453 does not contain "AIR", then it is a "spare space
index".

&8451 is an index of spare space at &858B. It is the offset from
&858B that spare space starts. &00 means that there are 64 bytes
of spare space starting at &858B+&00. >&3F means that &858B is
full.

&8452-&8453 is an index of spare space at &869F. It is the offset
from &869F that spare space starts. &0000 means that there are 297
bytes of spare space starting at &869F+&0000. >&12A means that
&869F is full.

If &8451-&8453 contains "AIR", then it is treated as though it
contains &000000.

I would also suggest that &858B-&85CA be used for data and
&869F-&87C9 be used for code, following the layout of the JSW48
game engine itself.

I would also recommend patches not be put in the rooms area, this
is space more valuable as rooms, and not in the sprites area, this
is more valuable as sprites.

--
J.G.Harston - jgh@... - mdfs.net/User/JGH
BBC IDE Hard Drive Interface - http://mdfs.net/Info/Comp/BBC/IDE

 

 

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