The Commodore 64 Assembler With A Deliberate Bug: Zeus64

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The Zeus 64 6510 machine language assembler package for the Commodore 64 has a bug lurking in it. Like, an actual digital bee or fly type thing that will buzz around your screen if you happen to send a particular instruction. Join me as we uncover this insect, and take a tour around its home, examining the features of this assembler and machine language monitor operating system.
The Zeus64 source code example is a port from my original Turbo Macro Pro source which I went on about in great detail in this previous video called "Commodore 64 Programming Joystick-Controlled Sprites in Assembly PART TWO" - • Commodore 64 Programmi...
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Index:
0:00 Intro, Zeus 64 package
3:05 Loading from cassette on PAL 64C
4:32 Depressing isn't it - legit?
5:39 First look at assembler
9:46 The Bug Easter Egg
16:32 Zeus 64: Differences to Turbo Macro Pro
23:32 Nice Zeus assembler features
27:14 Interesting Zeus ML monitor features
34:15 Summary and Thanks / Patron Credits

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3 авг 2024

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Комментарии : 103

@snowysnowdon5584 10 месяцев назад

I think the quote about being depressed is taken from Douglas Adams Hitch Hikers Guide To The Galaxy, namely Marvin the paranoid android. 😂

@FactorOfMatt 10 месяцев назад

I bought Zeus 64 directly from Crystal at a London, UK computer show in 1984. Where would I be without it? I found the "bug" almost immediately and even managed to find Crystal's phone number and asked them about it (possibly hoping there was a prize. There wasn't). I used Zeus for assembling C64 and C128 code well into 1988. It's quirky and a little cumbersome here and there but it works well and I'm so glad I found it. Things I remember: - Getting the most-significant byte of a word is possible using the up-arrow operator. So LDA #$ffd2 gets $d2, LDA ^$ffd2 gets $ff. It's mentioned on the second page of section 3 in the manual. -The source is tokenized in much the same way BASIC is, though I'm pretty sure it's stored as true-ASCII, not PETSCII. Things I just checked: - My copy (that I transferred to disk when I got a drive) says "Have a nice day!" when it boots - though it's possible I got clever and did that myself. - My C2N (or my '128) doesn't work. I was going to see if I did indeed muck with the greeting. The Marvin quote does ring a bell and I'm now insanely curious. Thanks for the video trip down memory lane.

@8_Bit 10 месяцев назад

Really cool to hear from someone who remembers the assembler, and even better, found the "bug" :) Do you remember if Crystal had anything else to say about it besides "no prize"? Zeus really does seem like a decent assembler.

@FactorOfMatt 10 месяцев назад

@@8_Bit I don't recall any specific mention of what the code was for, but I do remember them being most surprised that I found it (there was also some relief that this was the bug I was talking about, not some real showstopper issue). I've always just assumed that it was a simple debug routine to verify the assemble-loop was ticking over. Incrementing/decrementing a couple of VIC registers is minimal overhead and a welcome change from just incrementing the border colour. Update: Tried to load the tape using a C64 instead of the 128. The c2n motor at least spins now, but still no loading. Sure. I watch a video and now I need to fix things. :) Also: Until today I was convinced that I was the only person that had ever heard of Zeus.

@helgew9008 9 месяцев назад

@@FactorOfMatt If you can sample the cassette to a WAV file using an old boombox or something, it should be possible to make a TAP file from it.

@FactorOfMatt 9 месяцев назад

@@helgew9008 I'll give that a try. Thanks.

@fogvarious2478 9 месяцев назад

@@8_Bit Graham is still about, just doesn't do coding.. he was helpful when I was asking him about a game he made that I was taking apart.

@TheTRONProgram 9 месяцев назад

Great walkthrough overview, the Zeus Assembler looks most excellent. I Like that it shipped on Tape and let you hold multiple programs in memory and the line numbering feature.

@markpage2779 9 месяцев назад

I remember buying Zeus 64 from the local computer shop on tape, many years ago :)

@BikeArea 9 месяцев назад

How much did they take for it? 💵

@snaggle90 10 месяцев назад

Zeus was written by Crystal Computing == Design Design Software, put out some great games for the Spectrum in the day. They were well known for including easter eggs such as strange responses to high score tables and such things. Simon Brattel was involved, still on Facebook if I remember correctly.

@sark6502 10 месяцев назад

Apparently a different programmer wrote Zeus64 (under contract) - not Simon. Design Design wrote the Z80 version.

@snaggle90 10 месяцев назад

I stand corrected =)

@fogvarious2478 9 месяцев назад

crystal is not design design.. they worked together later.. Graham is probably behind this , he also can do z80 and 6502 (and other machines prolly) .. stupidly clever bloke, but humble with it. He went on after design design to start "walking circles" who did a fair few conversions. Zeus 128 was based on z64 .. that Mr Webb software creations made is based on it.. a PDS where you code on the c128 and send the code to the 64.. and save LOADS of ram for the game.. a number of games were made using it.. also even turned into a NES dev system for a while... Graham has done a fair bit on 8 bit , but it's not obvious :)

@ojjoooooo 10 месяцев назад

Should have been 0xBEE

@mikegarland4500 10 месяцев назад

Cool revisit. Liked the original, like this one as well. End credits song: pretty sure you've included that closing lyrical program before. I typed it in just to see what it did, and I KNOW I've seen you do that one before. Thanks for the update!

@8_Bit 10 месяцев назад

You may be the only person to have typed that song in! You're certainly the only person to have typed it in twice :)

@mikegarland4500 10 месяцев назад

@@8_Bit are you sure? or is it more like people just won't admit to typing it in? ;-)

@8_Bit 10 месяцев назад

@@mikegarland4500 You're right, I don't really know for sure :)

@MT-mi4zz 10 месяцев назад

@25:54 "This is kinda dangerous but I'll try it" - Whoa, easy there tiger...

@sark6502 10 месяцев назад

Hey Robin! Thanks for tracking this down! After 40 years I can finally put this mystery to bed.

@8_Bit 10 месяцев назад

It was a fun thing to look into; thanks for writing about your experience of it!

@WolfgangS 9 месяцев назад

Back in the time I used the Profi-Ass 64. This was heaven 😊

@SammYLightfooD 10 месяцев назад

There also was the HypraAss assembler which was distributed via the 64er magazine back then. It also uses basic line numbering for the source code. Back then I didn't know how to use it, just learned about it later - it's an interesting concept.

@CollinBaillie 10 месяцев назад

That ENT reference... 😂

@CptSparky 10 месяцев назад

You have easily become the most impressive channel on YT ❤ I love how you explain every little detail and dig out all that weird unknown exciting stuff 🥰👍 Thank you so much and I hope you'll keep up with the Commodore for a long time 🤗

@nickbungus 10 месяцев назад

If only i had Zeus when i was 14 years old. My life either have been different. Cassette too as no one had a disk drive in England.

@SimonCoates 10 месяцев назад

There were a few of them 😂

@G.B... 10 месяцев назад

Only rich people had a disk drive in 1984. It was almost as expensive as the C64 itself, so common mortals thought "ok, datasette it is". Many people got a second-hand drive later on, when Amiga became popular and people were selling their C64 peripherals since they didn't need them anymore.

@cygil1 10 месяцев назад

At least you had a c64. I had a TI that *boasted* as a feature that it was impossible to program in assembly. (You can, but you need a special GRAM module and software and the architecture is utterly incomprehensible to any but the high priesthood that understand a stream oriented architecture.)

@foxxy46213 9 месяцев назад

Everyone I knew who had c64 had a disk drive

@AndrewKroll 10 месяцев назад

I know what the Easter egg is all about. Let's remember the classic kid, writing asm for a few days straight and not taking a shower. What's the result? B0! Flies! B0, so surprising that nobody got that reference. 😂 Soon as I saw 176and the fly something clicked in my head because I have been dealing with hexadecimal all week, and somehow I converted that soon as I saw it. Thanks for showing us the egg, fun times!

@RacerX- 10 месяцев назад

Nice overview and demo. I had not heard of this one. Of course i was not much of a ML guy back then. It was something I was trying to learn with Commodore Assembler. I would love to see your take on COMPUTE!"s Fast Assembler.

@michielboland628 10 месяцев назад

Interesting, that brightness problem. I wouldn't think this is in the c64 itself. It looks like the capture tries to compensate for the amount of white in the picture. Haven't looked in great detail but it looked like an empty screen had a brighter background than a screen with white text. Could be interesting to see what happens if you use the standard colors (light blue on dark blue).

@Longuncattr 10 месяцев назад

Regarding the branch offset calculation command, there's at least one monitor for the 8-bit Atari machines with such a command as well, called Monkey Wrench. And it too does not have a mini assembler. Depressingly, it's not quite as useful as the command in Zeus, since the Monkey Wrench command requires you, as the first operand, to enter the address of the instruction *after* the branch instruction. So you have to do a bit of the 6502's incrementing logic manually. Kinda funny. :)

@donwald3436 10 месяцев назад

Assembly with line numbers, that's a mirror universe to line editing like `ed`.

@3vi1J 10 месяцев назад

Really surprised when you showed the tape. I didn't know any assemblers like this were distributed on tape. I was also surprised by some of the nice features. Insanely interesting and insightful, as your videos always are. Do you ever develop using a modern editor (like vs code + extensions+ ca65 or kick) and emulator for faster turnaround/testing? I've really enjoyed playing with the classic assemblers but was wondering what would be the most effective environment for development today. I've found there are quite a few cool opensource tools, like vchar64 and retrodebugger.

@8_Bit 10 месяцев назад

I have used ca65 on a couple projects, including an (unfortunately) unfinished game from about 3-4 years ago. For bigger projects it's definitely a good choice. For the smaller projects I work on for my videos, I just find it a lot more fun to program on the vintage hardware, and I think it makes the videos more interesting.

@3vi1J 10 месяцев назад

@@8_Bit It definitely is interesting to see the classic dev environments! If you're ever running low on ideas though, I'd love to see what someone with your experience thinks of/does with the modern tools. Keep being awesome!

@LeftoverBeefcake 10 месяцев назад

For a modern editor/assembler, CBM prg studio is pretty good because there's a ton of other things you can do with it, like creating sprites and screens and it has nice debugging features. I much prefer the Turbo Macro Pro assembler (due to Robin's videos) and thankfully it's available as a cross-assembler and can be used with your editor of choice... I use a Java-based editor called Relaunch64. The only assembler I've ever seen on tape is from HES (Human Engineered Software) called the 6502 Professional Development System. I have no idea how "professional" it is, though. It's still in the shrink wrap. :)

@3vi1J 10 месяцев назад

@@LeftoverBeefcake Yes, CBM prg studio is a cool tool. My only issues with it are it's closed source and Windows-only. I use Linux, which I somehow feel is the spiritual successor to the non-IBM systems of our youth. I've managed to get CBMPS working via WINE (which I've contributed code to in years past), but I prefer to work from native VS Code (as ironic as it is to use a MS editor) with ca65 and other tools on the back end. I also have tried Relaunch64 on Linux, but didn't find it as good as other environments.

@mikegarland4500 10 месяцев назад

I've also used CBM prg Studio myself, longer than any of the others. Once I got so far in it, I didn't want to take the chance of messing something up and stuck with it instead of trying to switch to any others that were recommended. Honestly, I'd probably still use it, since it's so powerful and has a ton of handy features. Just the ability to Copy & Paste in a native Windows environment has been so immensely helpful; I don't think I could have gotten this far in something like Turbo Macro Pro, even though I do like that one. I have reached almost 4k of code, and I'm wondering what I'm going to do next when I overflow that 4k block at 49152 ($c000)..

@LordmonkeyTRM 10 месяцев назад

That sir is a "busy" bee

@TrollingAround 10 месяцев назад

I seem to remember creating a disk version of Zeus by loading it and writing the RAM to disk and loading ,8,1

@NybblesandBytes 10 месяцев назад

2:55: "Vintage Computer Festival shirt..." -- whaa? Thinking you should have Jason make a shirt using that as the logo or something? O.o

@8_Bit 10 месяцев назад

The white and green design of the VCFMW 2022 shirt I'm wearing is reflected in the shiny black plastic below the cassette :)

@NybblesandBytes 10 месяцев назад

Hah -- nice. I didn't even notice! Now I can't unsee it! XD @@8_Bit

@mikegarland4500 10 месяцев назад

@@NybblesandBytes No idea what the original was supposed to look like, so it was just a garbled mess to my old eyes. 😞

@3vi1J 10 месяцев назад

@@8_BitOMG... I didn't even notice you mentioning it until I re-watched. Coincidentally I'm wearing my VCFSW 2023 shirt (which my wife insisted we buy to be twinsies) right now. lol

@dubbynelson 10 месяцев назад

0:59 remember when people wanted to write efficient software? i don't. i grew up in hell.

@cristianstoica4544 9 месяцев назад

I had the Zeus for spectrum. Interesting feel for typing. I don't remember if it had a disassembler.

@ScottyBrockway 10 месяцев назад

That's super weird the tape loader doesn't work on NTSC. I've never seen a single loader before that didn't. I'd love to see a dump of this tape so I can examine this loader.

@paulvanderlaak700 10 месяцев назад

Pfff I stay with my tass64. But thanks for sharing this oldie..

@PontusBerg 10 месяцев назад

I did note the ENT that was flashing by. :) A question on the OR issue. Is the same valid for AND? So could you have a label like BAND?

@uriituw 10 месяцев назад

That 64 has a green LED.

@G.B... 10 месяцев назад

Well, it's not exactly a bug, but rather a feature downgraded to an Easter egg. It would be better if the bee was always visible and moving while assembling (as a visual feedback that assembling is in progress). If nothing else, it's better than the flashing border lines TMP does while assembling. But other than that, while Zeus is certainly better than some other assemblers I have seen, I still think TMP is the best C64 assembler ever made.

@PaulTaylor1 9 месяцев назад

Yeah but in America, an insect is called a bug 👍😄

@andrewgale7731 10 месяцев назад

Have you ever tried the Fassem assembler? It used the BASIC editor to enter your code.

@ChrisM541 9 месяцев назад

Fantastic overview of this. I'm sure I used Zeus 64 in the mid 80's onwards, though I was using $C000 onwards (amongst other locations) for the assembled code. It appears, though, that Zeus 64 uses $C000 itself since I've just tried it out and can't assemble here (out of memory) though can assemble elsewhere. I'm wondering if Zeus 64 would allow some way of accessing $C000? Failing that, I might have used a cartridge e.g. the Mikro Assembler (which does allow assembling anywhere)? I really can't remember how I did it, lol. Subscribed.

@jan-erikkarlsson7875 6 месяцев назад

I think you really should take a look at Vision (Basic Compiler/Assembler/IDE) it seem's to come with everything ypu could want in a development Kit (Including running both natiively on C64 and cross, includes sprite editors etc.). Perhaps having an interview with the creator, he has a good youtube channel where he explains advanced techniques etc in Vision, it does require a REU of a certain size (uncerain what size is minium), how about some intro videos about the 'new' graphics modes etc that the c64 got late in its life.

@davidsantiagoalonso 10 месяцев назад

Strange, in 84 as kids in the play ground... We all had disk drives and cassettes. Disks for piracy, cassettes for magazines. A lot of people say that Aus had only cassettes, but not really. That was more of a UK thing possibly due to the zx being popular there, but i never saw one here ever! Apple c64 and the Amiga's Not even Ataris really... Then ofcourse pcs

@cygil1 10 месяцев назад

It really depends on the era. I believe by '87 the disk drive was ubiquitous, but not necessarily the early 80s.

@nysaea 10 месяцев назад

best spinning wheel ever

@suvetar 10 месяцев назад

Is it the screen brightness and changes or is the Font different? Edit: Is the Depressing message a quote from Marvin the Paranoid android, from Hitchhikers guide to the galaxy?

@mikegarland4500 10 месяцев назад

That's the assumption, but really no way to know for certain, I don't think. Unless the author comes forward to confirm it.

@vytah 10 месяцев назад

PAL and NTSC have different screen ratios

@ChrisR 10 месяцев назад

That green power LED seems....like it should be red?

@jonlegend9 9 месяцев назад

Hi, how do i remove the 10 rem bock from a tape game. I cant accsess the game anymore

@gregclare 10 месяцев назад

As the code does an AND #$FC before the CMP #$B0, I assume either 176, 177, 178, or 179 will work (i.e. $B0..$B3). Did you try this?

@3vi1J 10 месяцев назад

Since the AND discards these bits, they should basically do the same thing unless there's further code checking the low bits.

@gregclare 10 месяцев назад

@@3vi1J Exactly. As the Accumulator has been AND’d with #$FC, any subsequent code would only see 00 in the low two bits. Hence why I said the subsequent CMP #$B0 will work for an original A value of $B0 through $B3 (176 through 179).

@8_Bit 10 месяцев назад

It's actually been a while since I recorded this one but I think I did try $B1, $B2 and I'm pretty sure they did cause The Bee too. You can find Zeus on csdb dot dk and give it a try if you want to experiment.

@hugoegon8148 10 месяцев назад

20:00 Would "F0REVER" with zero instead of 'O' possible?

@talideon 10 месяцев назад

I wonder how much of the BASIC interpreter it's leaning on...

@PontusBerg 10 месяцев назад

It honestly looks quite different. The listing right align line numbers which basic surely doesn't.

@mcbpete 9 месяцев назад

4:32 (I'll try and write this comment without triggering the auto-moderation keywords that hit me the last few times !) You can see Tony Pomfret from Ocean using this assembler (with the same boot-up message) on the version of Commercial Breaks doc that Mark R. Cobley-Jones put on this site at around 8minutes 20 secs

@8_Bit 9 месяцев назад

It's unfortunate RU-vid goes to such great lengths to censor legitimate comments. Thanks for persisting, I'll take a look for that.

@8_Bit 9 месяцев назад

Awesome find! In case RU-vid will allow me to post a link, it's here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ChmQBK_EaUQ.html at about 8:20.

@grahamhansford2055 10 месяцев назад

I had the Zeus assembler, but I did not get the 'depressing' version. I do recall it being super super fast and easy to use. I never found the bug 'bug'. I think mine was called Zeus, rather than Zeus 64, but I do not recall. I do not recall the F command either. II'd like to know who wrote Zeus.

@grahamhansford2055 10 месяцев назад

and thank you for creating this.

@fogvarious2478 9 месяцев назад

the documentary about imagine / ocean... features it when tony pomfret is coding hunchback 2

@RonHelton 10 месяцев назад

👍👍👍👍💻💻💻💻

@mwk1 10 месяцев назад

Man, PLEASE HYDRATE! I see by the look at a palm of your hand that you're very dehydrated 😥Take care Buddy ❤

@DavidYoud 10 месяцев назад

K, who's going to type in the code Robin sings during the patreon scroll? :D

@mikegarland4500 10 месяцев назад

Uhh, you musta missed my early reply about it. I've typed it in twice. (I had forgotten what it did since the first video.) Wanna type it in and see? Or do you want the easy answer.. Or, I can give you the code and let you put it in yourself. Lots of options. 🙂 It's only 5 lines and about 180 characters, according to Notepad++

@DavidYoud 10 месяцев назад

@@mikegarland4500Nice! Yeah, post the code here please. :)

@mikegarland4500 10 месяцев назад

@@DavidYoud 10 b=49152:c=0 20 read a:if a > -1 then poke b+c,a:c=c+1:goto 20 30 sys 49152 40 data 169,147,32,210,255,169,0,141,32,208,141 50 data 33,208,238,32,208,238,33,208,76,13,192,-1 Have fun!

@DavidYoud 9 месяцев назад

@@mikegarland4500 I love that I can copy text and paste directly into VICE. Thanks for posting the code. :)

@mikegarland4500 9 месяцев назад

@@DavidYoud it is a handy feature, indeed. Glad to help in some small way.

@TheMoulie 10 месяцев назад

I suspect someone at Crystal was a Hitch Hikers Guide to the Galaxy fan as the quote is probably from Marvin the Paranoid Android. I bet your C64 has a pain in all the diodes down its left hand side.

@rinner2801 10 месяцев назад

And to think I did all my demo development using Acrion Reply Monitor :\

@fogvarious2478 9 месяцев назад

the action replay was still very useful.. you could use it with zeus 128 .. and debug code etc. or turbo assembler etc. coding in a cart monitor gave you a better understanding of stuff also i feel. just when it was bigger projects, not so easy

@gregmark1688 9 месяцев назад

I think you should know I'm feeling very depressed. Weirdly, I just finished watching the original Hitchhiker's Guide an hour ago, so yeah, I'm gonna say that's a reference to a certain paranoid android. Sounds perfectly awful. (Unlike Zeus64, which looks like a lot of fn!)

@csbruce 10 месяцев назад

5:51 They seem to have put a lot of effort into making bother lowercase and uppercase appear on the screen at the same time. 9:26 "New or Old" seems like a place where the user would often type the wrong thing. Why not just have the assembler know if there's a code in memory and have an explicit command to delete it? 10:35 A fly has bigger eyes. 10:56 Why not $BE? 20:20 "ORG" also contains the dreaded "OR" operator. 32:17 Seems like it should be easy enough to display the instruction as well as the address, considering they're using an entire screen line to show the address and have a built-in disassembler. 32:26 Clearing the screen fills the screen and color RAM and would take an eternity to execute like this. Why did it return to your $4000 code so quickly?

@gregclare 10 месяцев назад

20:20 the command parser would be testing for the valid reserved ‘ORG’ string, before testing for the shorter reserved ‘OR’ valid string.

@3vi1J 10 месяцев назад

What do you mean about 5:51? They appear to simply be in lower/upper case mode, as I see no PETSCII chars on screen. If you're in lower/upper case mode you can display lower and uppercase letters. It's only in upper/petscii mode that you can't display lowercase. As for 9:26... The assembler can't tell random garbage in memory from code/data. The N/O option just tells it whether it should re-initialize the end-of-program pointer to the beginning. They could have always assumed there's a program there and given you a "New" command to re-init the pointer, but that might have been confusing to users that assumed it would start with memory initialized on first load.

@csbruce 10 месяцев назад

@@3vi1J: They're mixing lower- and uppercase on the screen, with the code listings and everything the user types being in uppercase. This isn't the normal mode for Commodores, which use upper/graphics or lower/upper, with normal typing in the latter being in lowercase. This it indicates that they've written their own screen editor. Why? The only apparent benefit is to mix lower- and uppercase in the system messages.

@silkwesir1444 9 месяцев назад

@@csbruce tHINK again, there is an easier way to do that than to build your own screen editor... ;)

@aresaurelian 10 месяцев назад

The original title was supposed to be inspirational, not depressing. I think it is is a trolling meme, because assembling is magical and inspirational. I wonder what the original optional message said, that was more inspirational. Maybe it is a crypto puzzle : depressing the keys "isn't it" Oh, I get the bug reference now, that flying bug could be depressing.