Repton 3: Emulator/RNG issue

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Diminished
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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Tue Mar 31, 2020 8:40 pm

Rocketeer wrote:
Tue Mar 31, 2020 8:26 pm
The way I developed it was quite primitive since I didn't have a linker. A block of code is defined by a jump table of several JMPs into the actual routines themselves so I didn't have to keep changing addresses of those routines used in other assembler. In general the last JMP was the last routine hightest in memory so if you can find that and where it ends then the memory between that and the next set of JMPs should be free.
Ahhh. I wondered what those weird trampolines were for. Those were the things that initially made me think you had a lot of self-modifying code; I thought perhaps the jump targets were changed as the game ran. Then I thought maybe they were there because you had some shared code between the game and the editor, so they would jump to different places depending on which one was running. Then I thought perhaps they were a debugging aid, so you could perform vectoring at runtime by poking values into the jump targets. But no! Thank you, I should be able to cobble something together now.
Rocketeer wrote:
Tue Mar 31, 2020 8:34 pm
Dave, I can only conclude it got lost in the post then. I did send out the actual floppies probably five in total maybe more. Didn't have any machines to make backups on then so might have been touch and go even if they actually had arrived.
This is miserable news, though. :(

EDIT: all right, did a quick test using b-em's debugger and this looks promising:

Code: Select all

patch!

use 16-byte free region at &1df0:

lda #&ff
sta &85
sta &86
jmp &2fab

so ...

?&1df0 = &a9
?&1df1 = &ff
?&1df2 = &85
?&1df3 = &85
?&1df4 = &85
?&1df5 = &86
?&1df6 = &4c
?&1df7 = &ab
?&1df8 = &2f

then patch the jump target:

?&3034 = &f0
?&3035 = &1d
I'll test it a bit more tomorrow and then try to put together a release, provided someone else doesn't get there first.

EDIT2: here's the WFDIS file I used. Some of it is wrong but meh:
r3-2-6.wfdis.zip
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Just unzip it, then go here and upload it with the "select a file to disassemble" button. Warning: it may paralyse your browser for a while.

D

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Re: Repton 3: Emulator/RNG issue

Post by Snuggsy187 » Tue Mar 31, 2020 11:18 pm

Rocketeer wrote:
Tue Mar 31, 2020 8:26 pm


The way I developed it was quite primitive since I didn't have a linker. A block of code is defined by a jump table of several JMPs into the actual routines themselves so I didn't have to keep changing addresses of those routines used in other assembler. In general the last JMP was the last routine highest in memory so if you can find that and where it ends then the memory between that and the next set of JMPs should be free.
Nothing to add, just wanted to thank everyone contributing to this post. Most enjoyable. Those JMP routines did have me head scratching - seen similar in Codename Droid, I think.
=D>
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Re: Repton 3: Emulator/RNG issue

Post by skipchris » Wed Apr 01, 2020 9:33 am

Seconded — thanks so much for digging into this Diminished, and thanks for your thoughts, Matthew.

I have a whole host of questions, but for now please just bathe in my eternal gratitude.

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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Wed Apr 01, 2020 12:22 pm

No gratitude needed -- I'm stuck indoors on my own and slowly going mad, so distractions are welcome. Plus it was a good excuse to brave the uncharted realms of another classic title.

Patch. I made a simple level in the editor which I think exercises all of the game's features, and I also made eight trivial levels to check I could play through an episode without catastrophe. So I think this works, but I can't be 100% sure; the rest is in the hands of the experts.
Repton3_Diminished_Fungus_20200401_rc1.ssd
(97.75 KiB) Downloaded 11 times


Also did this, just so you know what you're playing.
screenie.png
I've not tested it with a joystick, neither on vintage hardware, nor on a Master 128 or anything.

Lunchtime!

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Re: Repton 3: Emulator/RNG issue

Post by skipchris » Wed Apr 01, 2020 1:23 pm

Works a treat in BeebEm masquerading as a Master!
Screenshot 2020-04-01 at 13.05.24.png
Past the fungus on Screen E.
Thank you so much!

Also, because no-one asked, here’s my splits for screens 1-4 of toccata.
IMG_3366 copy.jpg
splits

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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Wed Apr 01, 2020 2:01 pm

I'm glad. I think I'll pass on racing you, though. I think I beat screens A-D of Prelude as a child and then didn't get any further. Great game though, particularly with the editor. User-created content is king in gaming these days, so this was only 35 years ahead of its time.

That's the second bug in a >30 year old game I've found now (the first being the stack overflow in kieran's excellent Master 128 Prince of Persia port -- which, I should add, wasn't his fault).

I may dig deeper into the disassembly at some point since I've already started on it, and because it seems certain now that we won't be getting the original sources, sadly. The WFDIS file is up there if anyone else wants to poke around.

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Re: Repton 3: Emulator/RNG issue

Post by scarybeasts » Fri Apr 03, 2020 7:41 am

Rocketeer wrote:
Tue Mar 31, 2020 4:00 pm
The initial delay before the fungus seems right, I think that came at the request of Steve Botterill who found that if you had a screen with a lot of fungus to start with then it was on your case straight away. He wanted a fungus delay at the screen start so as not to make it too difficult.

IIRC there is a bug Richard Hanson told me about reported to him by a customer (don't know if it's documented) in that when you move into the crown at the game end then enter the map as Repton is moving, then return. The crown is gone and so the game doesn't end. I think it would have been corrected by swapping around two subroutines in the main loop. He did say it was so obscure that I was not to bother with it.
These little bits of history are fun -- thanks for dropping in to share :-)

Cheers
Chris

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Re: Repton 3: Emulator/RNG issue

Post by Michael Brown » Fri Apr 03, 2020 3:05 pm

Fantasic find and fix!

I hope you don't mind, but I have added that fix to my copy of Repton 3 on my Games Disc 024.
Could I please ask that someone play tests it to check it is OK as I cannot play games to that extent.

thanks
Mick.
Disc024.zip
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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Fri Apr 03, 2020 8:27 pm

The plot thickens.

It's been bothering me -- I just refused to believe this bug wasn't fixed at some point back in the day. Repton 3 was obviously very popular, else Superior wouldn't have seen profitability in releasing three expansion packs. Somebody had to have encountered this one on a normal playthrough, and surely it was reported at some point. It didn't seem possible that this had gone undetected and unfixed for three decades.

Fortunately there was a pretty easy way to check. The three expansion packs of course came bundled with their own copy of the game engine. If the bug had been found, it seemed likely that it would have been fixed in the sequels. With my emulator modification to print &85/&86 still in place, I grabbed Thru Time, Around the World in 40 Screens and Life Of from bbcmicro.co.uk and loaded them up. Sure enough, this bug was fixed, resetting the counter to &ff when a level is completed, and on all three titles.

You may be able to guess what happened next -- I downloaded the Repton 3 vanilla image from bbcmicro.co.uk. That one is fixed, too!

Meanwhile, the original dump that Bill Carr posted (thanks for the unadulterated copy, Bill!) has the bug intact.

So it looks like this is a Repton 2 situation, where a game-breaking bug was present in an earlier release version; ultimately several versions went out -- and my patch was unnecessary. The bbcmicro.co.uk version here appears not to have this problem (the site claims it's from PIAS2, which would make sense -- earlier on I was on the verge of trying to dig out my own PIAS2 tape to check this, but I didn't need to.)

This does make me wonder how the patch was applied -- did Matthew do it and reassemble, or was it (like my effort) an in-house Superior hack that borrowed some spare RAM somewhere? I also wonder whether PIAS2 was the only fixed vanilla R3 version, or whether Superior scuttled out a fix for the full-price version, in which case there should be an original "Repton 3" disc or tape out there somewhere that has this bug fixed. Obviously I have no idea if such a thing exists.

Archaeology!

EDIT1: I've taken RAM dumps after loading of both the Bill Carr and bbcmicro.co.uk versions. Using hexdump -C and then diffing the resulting outputs reveals a lot of differences -- this was reassembled rather than hacked, making a trivial side-by-side comparison difficult.

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Re: Repton 3: Emulator/RNG issue

Post by geraldholdsworth » Fri Apr 03, 2020 10:20 pm

It would be useful if there was a quick and simple way of identifying whether a copy has this bug fixed or otherwise.
I have original floppy copies of Repton 3, ATWIFS, LOR and RTT, so would be interesting to see if they have the bug.

(incidentally, I had also wondered if it had been fixed in house, as there was a competition number which could only be got if one completed the scenario without using passwords).
Gerald Holdsworth
Repton Resource Page
www.reptonresourcepage.co.uk

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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Fri Apr 03, 2020 10:37 pm

geraldholdsworth wrote:
Fri Apr 03, 2020 10:20 pm
It would be useful if there was a quick and simple way of identifying whether a copy has this bug fixed or otherwise.
I have original floppy copies of Repton 3, ATWIFS, LOR and RTT, so would be interesting to see if they have the bug.

(incidentally, I had also wondered if it had been fixed in house, as there was a competition number which could only be got if one completed the scenario without using passwords).
Yeah. One way would be to design a two-level episode, in which the first level can be completed trivially. The second level would need to contain some fungus, and you could beat the first level and then time the fungus to see if it begins to spread immediately, or only after a ten-second delay. A word of warning with this approach -- you need to spend enough time on the first level that the fungus counter has time to count all the way down, so you'd need to waste ten seconds on the first level in order for the test to be valid. One way to guarantee this would be to put down enough diamonds on Screen A that the player has to take at least ten seconds to collect them all. Then, watch the fungus on Screen B and see if it spreads immediately, or if it waits. You should be able to use the same level set on all versions of the game (at least I've had no problem loading my own test levels in all versions I've tried).

I'll attach my two RAM dumps in the interests of documentation. Surely some tool must exist for doing binary comparisons in this way (looking for bytes added and removed as well as just changed), but I'm not aware of one that produces something nicely human-readable like diff -u does for text files. There are significant differences, such as subroutine calls in certain places being removed entirely.

The dumps are just straight dumps of the whole 32K from 0 up to &7fff, so they'll match the addresses in the WFDIS file I posted upthread, but you'll get all the OS workspace and stack etc. at the start, and VRAM at the end. I think the actual game code starts at &400.
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Re: Repton 3: Emulator/RNG issue

Post by Snuggsy187 » Fri Apr 03, 2020 10:41 pm

Wow, and I thought it was nuts when I wrote Gerald's patch to cover the 87.5 versions of Electron Repton2 ! (missing diamond, bad monster count, or both, etc.) !

Good work Diminished, et al !
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Re: Repton 3: Emulator/RNG issue

Post by Rocketeer » Fri Apr 03, 2020 11:04 pm

Superior designed the bulk of the screens for all the variations, I designed a few and I think a few people like Tim Tyler designed many others.

I did supply a tool to them so that they could move screens around within the game file so they could design a screen, play test it then move it around to the position in the file they wanted it to be or combine screens from different game files etc. So it seems quite reasonable they would design a screen as the first screen in the file, test it then use the tool to move it around not realising that it was now so tight as to be unable to be finished.

Now from the analysis of the game images it seems that the bug was discovered and that they asked me to fix it but I don't recall at all if I was asked to do so and I'm pretty sure they never asked for the source to do it themselves.

Also, I did supply them with at least another tool that would read in a game file and calculate the code displayed at the end.

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Re: Repton 3: Emulator/RNG issue

Post by scarybeasts » Sat Apr 04, 2020 1:05 am

geraldholdsworth wrote:
Fri Apr 03, 2020 10:20 pm
It would be useful if there was a quick and simple way of identifying whether a copy has this bug fixed or otherwise.
I have original floppy copies of Repton 3, ATWIFS, LOR and RTT, so would be interesting to see if they have the bug.
I wonder if any of the existing disc tool software can output something like per-sector, per-track or per-disc checksums? A more thorough identification of different disc variants would be great for preservation efforts.


Cheers
Chris

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Re: Repton 3: Emulator/RNG issue

Post by Michael Brown » Sat Apr 04, 2020 9:09 am

That may explain why the code in my copy of Repton 3 was in a slightly different place from where you put yours ie &2FAB and &2FA5 etc.

Here is my original disc024.
Could someone please playtest this version to see if it contains a fixed version or not.
Originally, the game would have come from the tape, but on re-mastering a few years back, I may have used a disc version from later issues without realising the original fault.

regards,
Mick.
Disc024.zip
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Re: Repton 3: Emulator/RNG issue

Post by Kecske Bak » Sat Apr 04, 2020 9:18 am

My understanding was that the original tape version of Repton 3 for the BBC Micro was impossible to complete due to the fungus timer bug, that was fixed and Superior offered a replacement. However, in "Around The World in 40 Screens" the game engine was changed yet again so that the behaviour of spirits was slightly changed - how a spirit behaves if it is not against a wall at the beginning of a level - meaning some screens from later level packs don't work in the original Repton 3.

The "Majesty" bug is mentioned in the news section of "The Micro User" shortly after the release of Repton 3, so I'll have to go through the scans and find the article.

It's a shame Michael S. Repton isn't around because he could give chapter and verse on this.

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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Sat Apr 04, 2020 10:06 am

Michael Brown wrote:
Sat Apr 04, 2020 9:09 am
Could someone please playtest this version to see if it contains a fixed version or not.
Originally, the game would have come from the tape, but on re-mastering a few years back, I may have used a disc version from later issues without realising the original fault.
Hi Mick. Sorry to mess you around. I should have tested more versions before applying the patch.

I've tested this now, and your version was fine all along. My fault. I think I'm just going to make a test episode so there's a definitive way to check.
Rocketeer wrote:
Fri Apr 03, 2020 11:04 pm
I don't recall at all if I was asked to do so and I'm pretty sure they never asked for the source to do it themselves.

I think you fixed this one, Matthew, but I'm still hoping to find out what changed between v1 and v2. I think I've come up with a half-decent way of doing this now.
Kecske Bak wrote:
Sat Apr 04, 2020 9:18 am
The "Majesty" bug is mentioned in the news section of "The Micro User" shortly after the release of Repton 3, so I'll have to go through the scans and find the article.

It's a shame Michael S. Repton isn't around because he could give chapter and verse on this.
It would be interesting to see this, if you have the time to track it down.

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Re: Repton 3: Emulator/RNG issue

Post by billcarr2005 » Sat Apr 04, 2020 11:19 am

The differences are clear from the directory listing.
At &2FAB in D.REPTON2 on the PIAS2 disk is LDA#&FF : STA&86

On Mick's disc here viewtopic.php?f=1&t=18959&p=264237#p264218 LDA#&FF : STA &86 is located at &2FAA, so seems like yet another variant :shock:
REPTON 3.png
SAM 2.png
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Re: Repton 3: Emulator/RNG issue

Post by geraldholdsworth » Sat Apr 04, 2020 11:34 am

Kecske Bak wrote:
Sat Apr 04, 2020 9:18 am
It's a shame Michael S. Repton isn't around because he could give chapter and verse on this.
He's still around, just doesn't do much with Repton these days.
Gerald Holdsworth
Repton Resource Page
www.reptonresourcepage.co.uk

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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Sat Apr 04, 2020 1:19 pm

OK. Here's a test for whatever versions you lovely folks have. If you can complete Screens A and B then your version is bug-free. If you can't, it isn't. Because of the unpredictable way the fungus grows (i.e. sometimes it doesn't), it might be worth playing it twice, just to be sure.

Load the game up, then swap in this game disc. The file to load by pressing L at the menu screen is called "FUNGTST". I don't have a tape UEF available at this time so if anyone else transfers this to tape, please do post it.
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Re: Repton 3: Emulator/RNG issue

Post by Michael Brown » Sat Apr 04, 2020 1:20 pm

Hi,
no problem, if we find something wrong then we need to post it here for testing as there are enough of us to fix just about any issue.

Just one thing, did you try both D024's I posted or just the fix as if the original one I posted lastly was OK, then I can leave it as it is.
thanks
Mick.

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Re: Repton 3: Emulator/RNG issue

Post by geraldholdsworth » Sat Apr 04, 2020 1:22 pm

Diminished wrote:
Sat Apr 04, 2020 1:19 pm
OK. Here's a test for whatever versions you lovely folks have.
Nice.

Is it OK if I stick this onto the Repton Resource Page website?

Gerald.
Gerald Holdsworth
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www.reptonresourcepage.co.uk

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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Sat Apr 04, 2020 2:08 pm

Michael Brown wrote:
Sat Apr 04, 2020 1:20 pm
Hi,
no problem, if we find something wrong then we need to post it here for testing as there are enough of us to fix just about any issue.

Just one thing, did you try both D024's I posted or just the fix as if the original one I posted lastly was OK, then I can leave it as it is.
thanks
Mick.
Hi Mick,

The one I tested was the final one you posted, the one in this post. I've tested it again now just to make sure, and the bug is fixed.

Sorry for the confusion.
geraldholdsworth wrote:
Sat Apr 04, 2020 1:22 pm
Is it OK if I stick this onto the Repton Resource Page website?
Of course!

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Re: Repton 3: Emulator/RNG issue

Post by billcarr2005 » Sat Apr 04, 2020 3:47 pm

I had 4 disc copies of Repton 3, three with the gold "Superior Software DO NOT REMOVE" write protect stickers and one with plain black stickers.
The three didn't have LDA#&FF on sector &15D, offset &AB, but the other one did, so seems like a fixed version was released. That sleeve also contains a card to send off for Repton cuddly toys, of which Original, Arctic and Teenage were available, so seems that it was released after both ATWIFS and LOR.
REPTON 3 v2.png
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Re: Repton 3: Emulator/RNG issue

Post by Diminished » Sat Apr 04, 2020 4:09 pm

billcarr2005 wrote:
Sat Apr 04, 2020 3:47 pm
I had 4 disc copies of Repton 3, three with the gold "Superior Software DO NOT REMOVE" write protect stickers and one with plain black stickers.
The three didn't have LDA#&FF on sector &15D, offset &AB, but the other one did, so seems like a fixed version was released. That sleeve also contains a card to send off for Repton cuddly toys, of which Original, Arctic and Teenage were available, so seems that it was released after both ATWIFS and LOR.

REPTON 3 v2.png
Thanks a lot, Bill. Fascinating. You are doing the Lord's work here.

Do we have a reliable chronology of the release dates of R3 vanilla, the three expansion packs, and PIAS2? I suppose searching endlessly through BEEBUG scans would probably yield this information.

I am still trying to dig into R3 vanilla versus PIAS2. The changes are actually quite substantial in places. Some routines seem to have been reworked entirely. PIAS2 version even seems to have a shiny new interrupt handler that wasn't in the original, although working on this is painful and it's possible I've missed something. I haven't even found the fungus fix yet.

EDIT1: Yes, I see it now; Bill was quite right. It's in the routine I called Linit_level, predictably enough, just a couple of instructions in.

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Re: Repton 3: Emulator/RNG issue

Post by billcarr2005 » Sat Apr 04, 2020 5:47 pm

I wouldn't necessarily take Mick Brown's version as being from the Play It Again Sam 2 disc release, as it differs from the unadulterated copy i uploaded, not least in changing filenames...

EDIT: I've since checked through all of the original Repton disks I have, Repton 3 (v1 and v2), PIAS2 release, LOR, ATWIFS, RTT and all of them redirect the WRCHV (&20E + &20F) to &15CC (code at &151C). All of them also contain LDX #&0D : STX &FE00 at &154E, rather than INX - which explains the 1 byte difference from &15AB to &15AA on Mick's version :roll:
I guess in the mists of time the origin has been lost, but could explain the differences...

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Re: Repton 3: Emulator/RNG issue

Post by Michael Brown » Sun Apr 05, 2020 9:26 am

Hi,
I am not sure where my Repton 3 came from either.
I can confirm the fungus test works on it.
Strangely, Life of Repton and 40 Screens have identical code and the fungus test works on them.
My copy of Thru Time would not load FUNGTST and on checking the code was slightly different.
Made a new version of Thru Time using Repton 3 and FUNGTST loaded and worked.

Is it therefore possible that the fix to Repton3 came after the release of Thru Time?

Mick.

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Re: Repton 3: Emulator/RNG issue

Post by billcarr2005 » Sun Apr 05, 2020 11:54 am

RTT wouldn't even load the file?
I think the spirits move differently on later versions of the game, so replacing it with Repton 3 is probably not advisable.
RTT was the final game, after ATWIFS and LOR?
All of the original, unadulterated "expansion pack" disks I have contain the code LDA #&FF : STA &86 @ &2FAB

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Re: Repton 3: Emulator/RNG issue

Post by billcarr2005 » Sun Apr 05, 2020 12:28 pm

So I decided to check the Cheat it Again Joe disks, since they aim to work for all *released* versions of the game...
When I'd loaded the Repton 3 cheat, I was informed there were 2 distinct versions
ATWIFS and LOR were contained on CIAJ2, RTT on CIAJ3. All variants had the following code in the same place as V2 of Repton3

Code: Select all

VERSION1			VERSION2 / ATWIFS / LOR / RTT				Mick Brown's version
Stop timer
1EAA = 0			1EA9 = 0		SBC #01 to SBC #00		1EA9

Immortal to boulders
2A85, 2A86 = EA			2A85, 2A86 = EA		INC 78 to NOP:NOP		2A85, 2A86

View all maps
3046 = 20			304A = 20		CMP #05 to CMP #20		3052

Infinite lives
3119, 311A = EA			311C, 311D = EA		DEC 7F to NOP:NOP		311B, 311C



Immortal to spirits
595, 616, 680 = A9		597, 618 =A9		INC 78 / INC 78 to LDA#00
596, 617, 681 = 00		598, 619 =00

Immortal to lizards
697,558 = A9			698, 55A = A9		INC 78 / INC 78 to LDA#00
698,559 = 00			699, 55B = 00

Immortal to skulls/fungi
5C64,5C65 = EA			5C64, 5C65 = EA		INC 78 to NOP:NOP
Michael Brown wrote:
Sun Apr 05, 2020 9:26 am
I am not sure where my Repton 3 came from either.
EDIT: Thought I should check where the code needs changing on the original tape version... sure enough, same locations as Mick Brown's version, so it appears like that mystery has been solved :)
Last edited by billcarr2005 on Sun Apr 05, 2020 12:45 pm, edited 1 time in total.

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Re: Repton 3: Emulator/RNG issue

Post by geraldholdsworth » Sun Apr 05, 2020 12:45 pm

Michael Brown wrote:
Sun Apr 05, 2020 9:26 am
Is it therefore possible that the fix to Repton3 came after the release of Thru Time?
I have asked Richard Hanson about the history of this bug and it's fix. Hopefully, he may remember.

Cheers,

Gerald.
Gerald Holdsworth
Repton Resource Page
www.reptonresourcepage.co.uk

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