Reverse Engineering the PSX Copy Protection (Wobble Groove)

Members research, findings and information that can be useful towards the PlayStation 1.
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Post by Zyo117 » May 23rd, 2022, 11:24 am

Now I know that it's sort of bad form both to necro a topic as a first post, and also to continue to perpetuate a somewhat unbelieved bit of hearsay in the PSX world, but I started reading Sony's patent application for their copy protection, and it lead me down a somewhat interesting rabbit hole. According to their patent, the wobble groove is located in the TOC (table of contents) area of the disc, which on a standard CD, is between 23 and 25 millimetres from the centre point.

Now the part that interested me, is that on a standard CD-R, there is a section called the PMA, just before the TOC, at around 22.35mm to 23mm from centre. The PMA is a program memory area, used to store a temporary table of contents until the session is closed (the disc is burned) when the PMA is copied to the lead-in. Knowing the way CD-Rs work, this wouldn't have been able to be erased afterwards.

Now for the speculation section. I don't have a standard Ps1 disc to check with, but my thinking is that the wobble groove is pressed into the area where the PMA is on a CD-R. And now the part that's really interesting. According to the bloke from Paradox who gave MVG his info, a custom firmware was being run on the CD burner, which leads me to think they may have changed the burning process to eliminate the PMA cache, leaving that area of the disc open to modification. I'm not sure if you can burn a wobble groove into a disc, but perhaps the reason there was a specific model of burner chosen was for the strength of the laser.

Now speculation (mostly) aside, if anyone was planning to put a ps1 CD under a microscope, my guess is to look around the 22.35-23mm mark for the groove. According to Sony, as well, the groove should repeat the information several times.

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Post by Administrator » May 23rd, 2022, 8:14 pm

Zyo117 wrote: May 23rd, 2022, 11:24 am Now I know that it's sort of bad form both to necro a topic as a first post, and also to continue to perpetuate a somewhat unbelieved bit of hearsay in the PSX world, but I started reading Sony's patent application for their copy protection, and it lead me down a somewhat interesting rabbit hole. According to their patent, the wobble groove is located in the TOC (table of contents) area of the disc, which on a standard CD, is between 23 and 25 millimetres from the centre point.

Now the part that interested me, is that on a standard CD-R, there is a section called the PMA, just before the TOC, at around 22.35mm to 23mm from centre. The PMA is a program memory area, used to store a temporary table of contents until the session is closed (the disc is burned) when the PMA is copied to the lead-in. Knowing the way CD-Rs work, this wouldn't have been able to be erased afterwards.

Now for the speculation section. I don't have a standard Ps1 disc to check with, but my thinking is that the wobble groove is pressed into the area where the PMA is on a CD-R. And now the part that's really interesting. According to the bloke from Paradox who gave MVG his info, a custom firmware was being run on the CD burner, which leads me to think they may have changed the burning process to eliminate the PMA cache, leaving that area of the disc open to modification. I'm not sure if you can burn a wobble groove into a disc, but perhaps the reason there was a specific model of burner chosen was for the strength of the laser.

Now speculation (mostly) aside, if anyone was planning to put a ps1 CD under a microscope, my guess is to look around the 22.35-23mm mark for the groove. According to Sony, as well, the groove should repeat the information several times.
I'm certain it's not located where the TOC is. Every CD has a TOC. It's located where the ATIP is. CD-R's have a pre-recorded ATIP where as pressed PlayStation CD-ROM's have instead the wobble data. At least, that's my understanding.

The PMA sounds interesting and if a custom burner firmware was made it might be something which is possible. We'd have to look under a microscope or SEM. My theory is the PlayStaton CD-ROM mechanics might have a design flaw in them which results in the servos drifting and then finding and reading the 4 character string which makes the HC05 firmware pass validation.

Yes, the wobble repeats.
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Post by Zyo117 » May 24th, 2022, 7:09 am

Shadow wrote: May 23rd, 2022, 8:14 pm
I'm certain it's not located where the TOC is. Every CD has a TOC. It's located where the ATIP is. CD-R's have a pre-recorded ATIP where as pressed PlayStation CD-ROM's have instead the wobble data. At least, that's my understanding.

The PMA sounds interesting and if a custom burner firmware was made it might be something which is possible. We'd have to look under a microscope or SEM. My theory is the PlayStaton CD-ROM mechanics might have a design flaw in them which results in the servos drifting and then finding and reading the 4 character string which makes the HC05 firmware pass validation.

Yes, the wobble repeats.
The idea that it's around (not in exactly the same place but in the general area) the TOC actually comes from Sony's patent application for their anti-piracy. They might have been purposely vague on specifics, but that was the location they referenced.
In the preferred embodiment of the present invention, the system performs an initial check to determine whether or not the disc contains a “wobbled” code in the TOC (Table of Contents) area of the disc. In an authorized disc, the security code is repeated several times in order to ensure that it is properly detected without the need to add error correction bits to the security code. The system initially checks to determine whether the disc contains wobbling of the data in the TOC area of the disc before actually checking the actual code. If the disc does not contain a wobbled code, the system then determines if the disc is actually an audio disc. If it is an audio disc the system proceeds to play the audio disc and provide an audio output. If it is not an audio disc then the system shuts down.
If the disc does contain a “wobbled” code in the TOC area of the disc, the player proceeds to decode the wobbled code and transmit this decoded data to a mechanical controller. If the wobbled code matches a predetermined security code, then the system performs a second check on the disc for verifying authenticity. If the wobbled code does not match, the player then checks to see if the disc is an audio disc as noted above. If the disc passes the first code verification, the disc player then proceeds to verify that the disc contains a logo which matches a logo stored in the system. This second verification is performed to verify that the disc is actually authorized.
In the preferred embodiment of the present invention, the data bits which define the TOC (Table of Contents) area of the disc are stored such that a wobbled security code is embedded in the TOC track as a modulation of a physical positional offset from a nominal track location. The security code is stored by a process in which a 22.05 kHz signal is used as the modulation carrier wave which is digitally modulated in NRZ (Non Return to Zero) format to encode the security code.
According to the patent, the TOC bits on the disc are wobbled from a nominal track position, that wobble is the 'wobble groove', but its embedded directly into the TOC. Not to necessarily say you're wrong in thinking it's in a different place, but it seems to me that based on Sony's documentation that the understanding of how this all works is a little flawed? If the wobble groove is just a offsetting of the pits in the CD from the centre line, that should be entirely reproducible. It's not a groove, per say, as much as the information bits being intentionally not lined up.

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Post by Zyo117 » May 26th, 2022, 9:09 am

After studying the patent (US 6304971) several times, I think I have some idea how this works, now, and I'll just post it all in the one post to make it easy to understand. Basically, the wobble 'groove' doesn't exist. I don't know where that idea came from, maybe it was a suggestion early in in the PSX modding community and just stuck, but the term is a misnomer. The CDs aren't special other than being black. There's no data written to unwriteable parts of the disc.

Strictly according to the patent that Sony filed (and expired in 2015 by the way, so happy reverse engineering) the disc uses Sony's standard guide groove with a wobble of 22.05kHz (half of the standard audio sample rate of 44.1kHz). The game data is all written normally, however the TOC content is written in a special way. The bits that are written to the disc to comprise the TOC are burned in such a way that they don't line up with the centre of the guide groove. They mention using "22.05kHz modulation", which to my ears sounds like they essentially vibrate the laser opposite to the vibrations of the guide groove as the bits are being written. The laser, while reading the disc, does double duty: it checks if the data for the Table Of Contents wobbles, and if it does, proceeds to read the table of contents data, and read the 'wobble' of said data at the same time. These are read in NRZ (non return to zero) format: Areas where the data wobbles are a 0, areas where the data doesn't wobble is a 1. This is the 'wobble groove'. The system then checks for the presence of a logo as a second verification.

I want to be clear in saying that this is my simplified understanding strictly based on Sony's patent, with reference to Sony's patent for the CD guide groove, and throwing out everything I've 'learned' about it from YouTube and basic internet 'research'. This may not be exactly the implementation that Sony used in the PSX but given that they went into such specifics, I'd imagine they wouldn't deviate far from it for fear of being copied and not being able to legally defend their patent. If this can be verified by somebody with an IR microscope and a PS1 disc (IR can see through the dark purple plastic), well, that'll basically be the most public progress on reverse engineering the security in 28 years. No pressure, lol.

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Post by MottZilla » June 29th, 2022, 6:29 am

I think saying the wobble "groove" doesn't exist is just semantics. The "groove" is just one possible name for the section of the track/spiral that "wobbles" or introduces large tracking errors/corrections. The name for it isn't that important. I think it's generally considered to be true the basic points that somewhere near the beginning of the disc track a section exists that creates a specific pattern of tracking errors which are then interpreted into the SCEx code. Modchips work by injecting the needed signal later downstream.

The unknown are specific details about things like the tracking error and just general low level important facts. CD-Rs already have their spiral groove molded into the plastic. You can't change that, which is what you would need to change to cause the tracking errors/wobble to cause the hardware to generate the SCEx code.

If you want a writable disc that generates a SCEx code you'll have to get something custom manufactured. And if the area of the disc that is read to find the SCEx wobble is the ATIP then you may need a customized firmware for your burner. ATIP information could be assumed rather than read from the disc in which case the ATIP area could have the same wobble as a licensed disc. But there are various assumptions going on here.

Maybe if some weird flaw is exploited you could burn a working disc, but I personally think it would take purpose made CD-Rs to achieve it. And possibly a matching modified burner firmware.

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Post by alexfree » August 20th, 2022, 12:39 am

I have an alternative idea expanding on shadow's. It appears you can master CD-ROMs containg anything you want for a few hundred or thousand dollars now. As we know, Only CD-R/CD-RW have the ATIP, and normal CDROMs that are not PS1 discs do not have the wobble data where the ATIP is on CD-Rs. So technically if you really are determined, and IF the tracking errors don't matter that much and the console just wants to read i.e. SCEI from the area where on a CD-R would be the ATIP, then I wonder what would happen if you sent for CD-ROMs to be pressed, which for the first few sectors just have a spam of SCEI in the image you send the CDROM press company for use in mastering. In theory the PS1 is happy because it eventually reads SCEI from the expected area and then moves on to reading SYSTEM.CNF, etc.

If someone was crazy enough to attempt this, the only unknown I see is how many times do you spam SCEI in this example? Do you figure out a normal CD-R ATIP length and just do the same?

An alternative idea back to CD-Rs is if you can absolutely control the exact data of the TOC, maybe you could prepend the SCEI code in front of the actual data. The PMA is a "temp" copy of the TOC that is burned when a multisession disc is not closed but at least one session has been burned. It is even earlier then where the TOC normally is on a CD-R, so if anything would work on a conventional CD-R due to servo tracking not being that exact I think this would be it. But does this require modded CD burner firmware or drivers? Both?

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Post by MottZilla » August 20th, 2022, 7:39 am

I don't know the exact process of how you get discs mastered, but the SCEx isn't data in an ISO image or other type of disc image you'd likely be sending the company to master your disc. So you'd have to talk to whomever makes the actual glass master about modifying it to have the wobble in the correct place. I'm sure that would be a long conversation.

Again I don't know how the process usually works but I would imagine they expect you to send them either a disc image (such as ISO+CUE) or an actual CD-R for them to then generate a master from. Since the wobble is a modification of part of the data spiral you'd need to talk to the people in charge of actually making the glass master to see if it's possible for them and that they are willing to modify the process so you can get your disc mastered with the security wobble in place.

In theory you could press discs with all three SCEx codes to make a nearly region free disc. You'd need the Japanese License text to boot on those machines, though it would leave out late PAL machines that have their own license check. But atleast the cd-rom controller would be happy regardless of the region. You'd need a Action Replay/GameShark to skip the license data check in the BIOS shell for whomever ends up unhappy with the license text chosen.

Then you could have a new "boot disc" to replace things like Breaker Pro or PS-X-Change. But it would be an expensive thing to do and likely you wouldn't recoup your losses unless you planned to use the security wobble modification on other discs you would sell. So it would make more sense to figure out the wobble if you wanted to make and sell unlicensed games to help make back the cost.

It would be amazing if someone with detailed knowledge of the low level workings of all this could actually figure out a way to do it with standard CD-Rs. But I'm not gonna hold my breathe.

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Post by alexfree » August 20th, 2022, 1:49 pm

MottZilla wrote: August 20th, 2022, 7:39 am I don't know the exact process of how you get discs mastered, but the SCEx isn't data in an ISO image or other type of disc image you'd likely be sending the company to master your disc. So you'd have to talk to whomever makes the actual glass master about modifying it to have the wobble in the correct place. I'm sure that would be a long conversation.

Again I don't know how the process usually works but I would imagine they expect you to send them either a disc image (such as ISO+CUE) or an actual CD-R for them to then generate a master from. Since the wobble is a modification of part of the data spiral you'd need to talk to the people in charge of actually making the glass master to see if it's possible for them and that they are willing to modify the process so you can get your disc mastered with the security wobble in place.

In theory you could press discs with all three SCEx codes to make a nearly region free disc. You'd need the Japanese License text to boot on those machines, though it would leave out late PAL machines that have their own license check. But atleast the cd-rom controller would be happy regardless of the region. You'd need a Action Replay/GameShark to skip the license data check in the BIOS shell for whomever ends up unhappy with the license text chosen.

Then you could have a new "boot disc" to replace things like Breaker Pro or PS-X-Change. But it would be an expensive thing to do and likely you wouldn't recoup your losses unless you planned to use the security wobble modification on other discs you would sell. So it would make more sense to figure out the wobble if you wanted to make and sell unlicensed games to help make back the cost.

It would be amazing if someone with detailed knowledge of the low level workings of all this could actually figure out a way to do it with standard CD-Rs. But I'm not gonna hold my breathe.
What I would want to try though is just spamming SCEX in the first few sectors that the CD-ROM can possibly contain, it would literally be nothing but SCEX in hex data for the earliest few sectors that can be pressed to the CD-ROM which should be before an ATIP normally would reside on a CD-R. I don't want to try to emulate the wobble, or an ATIP. Just have something like SCEISCEISCEISCEISCEISCEI (on and on and on from the earliest sector to maybe the 3rd). It in theory shouldn't work, but I really think maybe it could. It is a different take on Shadow's idea.

My understanding is that mastering a disc allows us to have whatever data we want where the ATIP is normally on CD-R discs because CD-ROMs do not have such an area (normally, PSX discs are sort of an exception). I wouldn't even try to do the wobble stuff, just strictly have SCEX in the first possible place data can be pressed to on the CD-ROM. It might be so dumb it works, the main benefit to this kind of copy protection seems to be it prevents CD-R discs from booting normally because it is impossible to change what the ATIP says. I think the whole system might not be as smart as it seems however, maybe just reading SCEX data a few times from the same location where ATIP normally would be would suffice. And since it is a CD-ROM being pressed, my understanding is that we can write to where the ATIP is normally on a CD-R, which might be enough.

I don't really know much about pressing discs either. But I don't think you would even need to have a conversation about what you want the disc to contain. It would just contain your BIN+CUE equivalent image.

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Post by MottZilla » August 20th, 2022, 2:08 pm

The SCEx code is not data on the disc or in sectors. Your BIN+CUE image has nothing to do with it. The SCEx code is generated by the (most likely) extreme tracking errors on the spiral of the data track near the beginning of the disc. The spiral instead of tracking in a smooth line "wobbles" back and forth which is then translated into a bit stream that becomes the SCEx code. On a normal disc when spin-up begins and the laser tracks the disc spiral, only minor tracking corrections take place to keep the laser on target. On a real Sony factory pressed disc the wobble in the spiral causes a specific series of tracking corrections which get converted and eventually end up in that bit stream I mentioned earlier that forms the SCEx code.

This is why a modchip has to gate off the signal coming from real playstation discs in order for them to boot. If you don't stop the signal being generated by the real disc, the modchip and disc will be sending conflicting signals and the drive won't authenticate. But a CD-R will work without the gate since it shouldn't generate any signal.

So this is why I'm saying you'd need to take to whomever is in charge of making the master and seeing if it's even possible for them to modify the disc spiral in this way to make a bootable disc. Even if they can do it, then someone has to do the work to figure out exactly how to modify it. Obviously it can be done, Datel did it.

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Post by alexfree » August 30th, 2023, 2:04 pm

I've dug into the cdrdao source code quite a bit, and I do wonder something. The lead in data is written as zero data (per spec), but it doesn't actually have to be zero data. It could be hacked on to write anything during the burn. Since 80 minute CD-Rs have tighter spiral windings, and there is the possibility of servo drift, I really wonder. That or the PWA thing would be the only real ideas I would think have any chance of working. The thing about the custom lead-in data though is AFAICT it doesn't actually need any modified burning firmware, just hack on cdrdao source code.

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Post by nocash » August 31st, 2023, 12:18 pm

A complete copy of the US6122739 patent - with images - can be found here https://patentimages.storage.googleapis ... 122739.pdf it's referring to "wobble" and "wobbling" in the "radial direction", and the images (FIG.2B and FIG.3) are illustrating how the wobble should look like under a microscope.

I can't find any good pictures that are showing how the normal CDR wobble should look like... now I am wondering if that's the same kind of wobbling at all (especially as the PSX wobble appears to generate that audible sound in the drive mechanics, I guess regular CDRs won't do such things).

---

Trying to mimmich the wobble by writing nonzero data, that might work, perhaps the data on the current spiral winding (or adjacent spiral windings) could cause wobble-like effects.

If you want to try that, first make sure that your drive can actually read & write nonzero data in lead-in TOC area.

Next, how low-level can you go? If you can control the laser directly would be fantastic (or somehow controlling the laser intensity in real-time might do the same thing).
But I guess typically the lowest level is writing CDDA audio, which brings up several problems:

- Data Bytes with "8bits" are burned as "14bit symbols"
- Data Bytes are bundled with some error correction info (even on CDDA audio discs)
- Data Bytes are (probably, not sure) re-ordered for better error correction results.
- Data Bytes are also mixed with Sub-Channel bits here or there.

So it may be impossible to do things like buring "a series of 1 bits" followed by "a series of 0 bits". At best, you could hope for finding a way to burn a "series of bits with high quantity of 1 bits". But it would require a lot of very complicated maths to compute a sector that would result in such effects. And there isn't even much of chance to verify the result - except by using an oscilloscope to watch the laser signals.

---

Anyways, I just had another idea: The hardware can move the lens inwards and outwards, normally it's doing that in a fashion that will follow the spiral windings.
But with a small extra circuit, one could tweak the CDR-burner to push the lens inwards (and/or outwards) instead of perfectly following the spiral windings.

When doing that, the drive would respond by trying to move the lens back to the center... I don't know if that's a problem... Maybe a short push is enough, or otherwise one could increase the strength to prevent the drive from compensating the error (or if the drive is unable to compensate fast enough, then one might even need to take care of pushing the lens back in opposite direction).

---

EDIT: After re-reading the posts from 2020-2021. Uhm, my thoughs and findings aren't as new as I thought.
dimosz had already posted a complete copy of the pdf patent, and bennvenn did also had the same idea about injecting the signal to a modified drive during the burning process.
Last edited by nocash on August 31st, 2023, 12:58 pm, edited 1 time in total.

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Post by alexfree » August 31st, 2023, 12:52 pm

nocash wrote: August 31st, 2023, 12:18 pm A complete copy of the US6122739 patent - with images - can be found here https://patentimages.storage.googleapis ... 122739.pdf it's referring to "wobble" and "wobbling" in the "radial direction", and the images (FIG.2B and FIG.3) are illustrating how the wobble should look like under a microscope.

I can't find any good pictures that are showing how the normal CDR wobble should look like... now I am wondering if that's the same kind of wobbling at all (especially as the PSX wobble appears to generate that audible sound in the drive mechanics, I guess regular CDRs won't do such things).

---

Trying to mimmich the wobble by writing nonzero data, that might work, perhaps the data on the current (or adjacent spiral windings) could cause wobble-like effects.

If you want to try that, first make sure that your drive can actually read & write nonzero data in lead-in TOC area.

Next, how low-level can you go? If you can control the laser directly would be fantastic (or somehow controlling the laser intensity in real-time might do the same thing).
But I guess typically the lowest level is writing CDDA audio, which brings up several problems:

- Data Bytes with "8bits" are burned as "14bit symbols"
- Data Bytes are bundled with some error correction info (even on CDDA audio discs)
- Data Bytes are (probably, not sure) re-ordered for better error correction results.
- Data Bytes are also mixed with Sub-Channel bits here or there.

So it may be impossible to do things like buring "a series of 1 bits" followed by "a series of 0 bits". At best, you could hope for finding a way to burn a "series of bits with high quantity of 1 bits". But it would require a lot of very complicated maths to compute a sector that would result in such effects. And there isn't even much of chance to verify the result - except by using an oscilloscope to watch the laser signals.

---

Anyways, I just had another idea: The hardware can move the lens inwards and outwards, normally it's doing that in a fashion that will follow the spiral windings.
But with a small extra circuit, one could tweak the CDR-burner to push the lens inwards (and/or outwards) instead of perfectly following the spiral windings.

When doing that, the drive would respond by trying to move the lens back to the center... I don't know if that's a problem... Maybe a short push is enough, or otherwise one could increase the strength to prevent the drive from compensating the error (or if the drive is unable to compensate fast enough, then one might even need to take care of pushing the lens back in opposite direction).
The audible sound only occurs on later consoles, it never happens on SCPH-1001 or lower. I think that became a thing once they consoles could do auto bias+gain calibration (so IIRC SCPH-550X and newer). Of course that doesn't really impact the copy protection mechanism.

CDRDAO can write in raw mode using the generic-mmc-raw driver, you can literally write whatever you want. Even invalid sector sync data from what I understand (I see zero reason why that won't work). The problem does remain however, what do the wobble sectors look like? I can go ahead and hack on cdrdao source code to write whatever lead-in data we want in theory, but what would I write instead of zero filled sectors?

I think it makes the most sense to try writing a bunch of non-zero bytes instead of a zero filled lead-in and to see if that actually works when ripped raw (lead-in is included in a raw rip with the right arguments to cdrdao). But again, I think how do we convert an oscilloscope read to the equivalent raw sector data? That is the real issue.

That hardware stuff is definitely out of my league, but what your saying should work I would think!

Thanks for the review on my idea.

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Post by nocash » August 31st, 2023, 2:39 pm

No, you can't "convert the oscilloscope read to data". I meant that "you must convert the data yourself", based on the sony patent and on the cdrom specs. And thereafter, you could use the oscilloscope to verify if you have actually converted it as planned.

Wiring a oscilloscope to the optics to see if you have written a 11111111110000000000 pattern should be easy, but it would probably take you some weeks (months?) of research & maths to figure out how to create a disc image that will produce anything that will resemble that kind of pattern.

Cdrdao "raw" data is just what you have in regular disc images. That binary "bits" are miles away from the "optical dots" on the disc surface.

Let's say you want to burn a 11111111110000000000 pattern, you will need to do a lot of research about the lower-than-commonly-known-low-level disc structure, write some conversion software that recurses the 14bit symbols, error correction, sub-channel interleaving and so on. After doing that, you will probably find out that writing 11111111110000000000 isn't possible, but you could perhaps write 11011101110010010100 (and hope that that's close enough), to do that, you might, for example, need to store something like 45 C2 F7 9A at specific location(s) in the disc image.

I really don't know how to do such things exactly, but it's almost certainly very very difficult. And keep in mind that - in theory - the data burning idea can't work anyways. Unless you can somehow melt specific sections the disc surface deeply enough that the PSX drive will accidently start to wobble as a side-effect.

The hardware modification idea is much easier: It's basically a regular modchip shortcut with one of the tracking signals on a regular CD burner (or a modified modchip that outputs 22.050kHz pulses instead of using constant levels for the ASCII bits, and perhaps some resistor or capacitor to avoid a direct shortcut) (and of course raise all timings when using a buning speed higher than 1x).

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Post by david4599 » September 1st, 2023, 8:03 am

nocash wrote: August 31st, 2023, 12:18 pm I can't find any good pictures that are showing how the normal CDR wobble should look like... now I am wondering if that's the same kind of wobbling at all (especially as the PSX wobble appears to generate that audible sound in the drive mechanics, I guess regular CDRs won't do such things).
On the ECMA-394, it is said the wobble has an amplitude of only 30nm and a spatial period of 54 to 64um.
So, even with excellent pictures, I guess it would be impossible to see it to the eye.

Yes, the PS1 discs have the same wobble, just the modulation is changing.
FYI, Datel did modify factory machines not to use the ATIP generating machine but a microcontroller to switch on and off the 22kHz. As simple as that.
https://www.youtube.com/watch?v=XUwSOfQ ... omF4AaABAg
Comment on how Datel produced PS1 discs.png
alexfree wrote: August 30th, 2023, 2:04 pm I've dug into the cdrdao source code quite a bit, and I do wonder something. The lead in data is written as zero data (per spec), but it doesn't actually have to be zero data. It could be hacked on to write anything during the burn. Since 80 minute CD-Rs have tighter spiral windings, and there is the possibility of servo drift, I really wonder.
Don't waste discs and time on that.
Changing the sectors data in the lead-in by choosing the EFM symbols will not disturb the tracking signal of the PS1 pickup enough if at all. EFM is used to avoid synchronization errors and it is impossible to write tens or hundreds of 1 at once using this encoding. Also, the EFM conversion is done in the burner, possibly hard-coded in the DSP itself, not in the firmware. The burning softwares, even set in raw mode, have no control on that.

I remember the cdimage project that is able to draw images on CDs using only 4 EFM symbols that have a different numbers of 1 (from what I understood) allowing to create 4 shades (I guess, not tested) visibles to the eye. The created file just needs to be burned in audio mode i.e. without scrambling. That's the best we can do using the conventional way.
https://github.com/arduinocelentano/cdimage

Instead I found another solution. Usually I don't post until something is mostly finished but I already teased a bit on Twitter so here we go:

To change the tracking signal, like nocash said, we indeed have to either take control on the laser and burn longer non-EFM pits/lands or input a foreign signal into the tracking coils of a burner.
In both cases, we also need to "remove" the original 22kHz wobble of a CD-R otherwise the signal will still be 1. This can be done by increasing the pits and lands length meaning that the disc will spin faster natively and the 22kHz will not be detected anymore by the PS1 when the custom pattern will be read.

I worked quite hard on that crazy project trying to experiment these ideas and I have finally great news!
2 months ago, I succeed in simulating the SCEx wobble and thus creating a self-bootable CD-R by using the first way I mentioned! :D



(The reading struggle when loading the game I'm talking about is mostly due to the disc spinning faster than usual, combined with this Verbatim CD-R and also the pickup itself I think)

For now, it works only on one of my 5502 and it is really not stable (maybe 1 of 20-30 tries).
I'm still trying to improve that but it's really dfficult to modify the burner's firmware, know what the code is doing, figure out the unknown DSP commands (many of them will never be known because the datasheet is not public) in order to properly adjust some code without killing another laser diode. Ideally, a software mod would be nice but maybe a hardware mod can be easier to achieve a better result. I think I will try to solder some wires soon.

And I still have to write these blog posts... But I'm lazy...

Oh btw I was informed that this was done 20 years ago on a private forum! I was not the only one to achieve it and I was convinced about that, though it was also unreliable apparently. I don't know the method they used but probably one of the two said before.
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Post by alexfree » September 1st, 2023, 1:07 pm

david4599 wrote: September 1st, 2023, 8:03 am
nocash wrote: August 31st, 2023, 12:18 pm I can't find any good pictures that are showing how the normal CDR wobble should look like... now I am wondering if that's the same kind of wobbling at all (especially as the PSX wobble appears to generate that audible sound in the drive mechanics, I guess regular CDRs won't do such things).
On the ECMA-394, it is said the wobble has an amplitude of only 30nm and a spatial period of 54 to 64um.
So, even with excellent pictures, I guess it would be impossible to see it to the eye.

Yes, the PS1 discs have the same wobble, just the modulation is changing.
FYI, Datel did modify factory machines not to use the ATIP generating machine but a microcontroller to switch on and off the 22kHz. As simple as that.
https://www.youtube.com/watch?v=XUwSOfQ ... omF4AaABAg
Comment on how Datel produced PS1 discs.png
alexfree wrote: August 30th, 2023, 2:04 pm I've dug into the cdrdao source code quite a bit, and I do wonder something. The lead in data is written as zero data (per spec), but it doesn't actually have to be zero data. It could be hacked on to write anything during the burn. Since 80 minute CD-Rs have tighter spiral windings, and there is the possibility of servo drift, I really wonder.
Don't waste discs and time on that.
Changing the sectors data in the lead-in by choosing the EFM symbols will not disturb the tracking signal of the PS1 pickup enough if at all. EFM is used to avoid synchronization errors and it is impossible to write tens or hundreds of 1 at once using this encoding. Also, the EFM conversion is done in the burner, possibly hard-coded in the DSP itself, not in the firmware. The burning softwares, even set in raw mode, have no control on that.

I remember the cdimage project that is able to draw images on CDs using only 4 EFM symbols that have a different numbers of 1 (from what I understood) allowing to create 4 shades (I guess, not tested) visibles to the eye. The created file just needs to be burned in audio mode i.e. without scrambling. That's the best we can do using the conventional way.
https://github.com/arduinocelentano/cdimage

Instead I found another solution. Usually I don't post until something is mostly finished but I already teased a bit on Twitter so here we go:

To change the tracking signal, like nocash said, we indeed have to either take control on the laser and burn longer non-EFM pits/lands or input a foreign signal into the tracking coils of a burner.
In both cases, we also need to "remove" the original 22kHz wobble of a CD-R otherwise the signal will still be 1. This can be done by increasing the pits and lands length meaning that the disc will spin faster natively and the 22kHz will not be detected anymore by the PS1 when the custom pattern will be read.

I worked quite hard on that crazy project trying to experiment these ideas and I have finally great news!
2 months ago, I succeed in simulating the SCEx wobble and thus creating a self-bootable CD-R by using the first way I mentioned! :D



(The reading struggle when loading the game I'm talking about is mostly due to the disc spinning faster than usual, combined with this Verbatim CD-R and also the pickup itself I think)

For now, it works only on one of my 5502 and it is really not stable (maybe 1 of 20-30 tries).
I'm still trying to improve that but it's really dfficult to modify the burner's firmware, know what the code is doing, figure out the unknown DSP commands (many of them will never be known because the datasheet is not public) in order to properly adjust some code without killing another laser diode. Ideally, a software mod would be nice but maybe a hardware mod can be easier to achieve a better result. I think I will try to solder some wires soon.

And I still have to write these blog posts... But I'm lazy...

Oh btw I was informed that this was done 20 years ago on a private forum! I was not the only one to achieve it and I was convinced about that, though it was also unreliable apparently. I don't know the method they used but probably one of the two said before.
This is literally insane. I have so many questions:

1) Is it possible to make one universal bootable disc this way? With SCEI/SCEA/SCEE all on the same disc? That has never been done AFAICT but IIRC no cash said in the SPX it was theoretically possible.

2) Have you tried using good CD-R media and not 'fake verbatims'

3) When you say the disc spins faster then usual, that is a constant (not just when reading the wobble)? So that screws up the seek times?

4) Would it make sense to make a bootable Tonyhax International CD-R, so that once it self-boots you can play games properly without the disc spinning faster? Would discs that have been swapped while using Tonyhax International run at the right speed because they don't have the longer pits/lands that the self-booting Tonyhax International CD-R has? Does it matter if the drive door is never opened/closed in this scenario (from what the PSX can sense anyways, because for Japanese consoles the idea is to leave the lid sensor blocked and swap in a CD-R from a real disc).

5) Can you explain more on what actually creates the SCEX signal?

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Post by nocash » September 1st, 2023, 6:03 pm

1) I am quite sure that there are already modchips doing that, that's nothing new.
3) How on earth could the spindle speed affect the sled seek times??? Faster rotation is only needed in Lead-in, doing it elsewhere would cause issues on movie/audio streaming timings.
4) It's just a normal disc with SCEx, same as retail discs, it won't behave different if you open a door.
5) We have the patent, and mod chip source code, and this thread, more info isn't possible. At best, you could ask for less info.
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Post by nocash » September 1st, 2023, 6:44 pm

david4599 wrote: September 1st, 2023, 8:03 am So, even with excellent pictures, I guess it would be impossible to see it to the eye.
I can't even find a simple drawing, like those in the playstation pdf patent file.
As far as I understand, the 22kHz wobble is everywhere on CDRs (as timing mark), and there's some kind of additional wobbling for ATIP bits? Or are they using absence of wobbling for ATIP bits, similar as for the SCEx bits?
david4599 wrote: September 1st, 2023, 8:03 am we also need to "remove" the original 22kHz wobble of a CD-R otherwise the signal will still be 1. This can be done by increasing the pits and lands length meaning that the disc will spin faster natively and the 22kHz will not be detected anymore by the PS1 when the custom pattern will be read.
Oh, okay, that might be a problem. I don't know what problems would arise when changing the disc speed with external hardware on drives with unmodified firmware.

How much do you need to increase the rotation speed?

Would it be possible to filter-out the 22kHz tracking error wobble, so the drive would simply ignore it?
Then you could perhaps burn a straight line (and apply your own SCEx wobble where needed, or disable the filter in that places).
That might work even when using normal rotation speed (hoping that the burned signal would override the original pre-groove wobble).
david4599 wrote: September 1st, 2023, 8:03 am I think I will try to solder some wires soon.
Good luck there, I hope it will work!

Btw. did you try the burned CDR on a console with modchip? Just in case you've accidently made the TOC reading or data reading unreliable, causing problems unrelated to SCEx reading.

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Post by david4599 » September 2nd, 2023, 11:37 am

1) Yep, I can literally burn almost any pattern but burning the 3 words will be even less reliable until I can find how to solve the other issues.

FYI, Datel did exactly that, here is a capture of the breaker pro I have (blue = tracking signal CL709 on PU-18, yellow and pink = SCEx signal and gate output where modchips wires are soldered to):
DS1Z_QuickPrint131.png
2) I have the printable datalifeplus AZO Verbatim but in lower quantity than these "extra protection" ones. For the wobble check, these discs seem fine but I'm still thinking to try the "Taiyo Yuden" ones.
I just checked and compared these disc types against the two 5502 I have and I can confirm that their drives (one original and one "made in china") are not great especially the old original one hence the reading issue in 2x mode in the video.

3) Yeah, the speed is increased everywhere. Right now, I'm working on trying to change the pits/lands length while burning by adjusing the laser speed setting thanks to the right DSP command.
It suprisingly kind of works, the PS1 auto-adjusts the spindle speed when recognizing different pits/lands length but a few sectors can't be decoded if the change is too sudden. I guess I have to do smaller steps.

4) This wouldn't be useful if I can manage what I said just before, but why not. Yep, the swapped discs will spin at normal speed since their pits/lands length is normal.

5) Like the former Datel engineer says in the comment, it's just the 22kHz sine wave normally used for CD-R/RW that will be switched on and off accordingly to the SCEx bitstream.
Now, if you mean how my pattern creates it, basically I'm overwriting existing data with huge pits, the photodiodes of the drive just receive less (or more?) light every 23us (half a period of 22kHz).
This will produce a voltage change every 23us in the resulting tracking signal that the 22kHz filter of the PS1 (made specifically for the SCEx wobble detection) is able to see.
nocash wrote: September 1st, 2023, 6:03 pm Faster rotation is only needed in Lead-in, doing it elsewhere would cause issues on movie/audio streaming timings.
A CD player is searching for the good pits/lands frequency and will automatically adapt the spindle speed (CLV mode). If the pits/lands are burned longer, the player will just increase the speed and the bitrate will stay the same (176kbps in 1x and 353kbps in 2x), musics and movies timings won't change. The donwnside is that the disc can hold less information since the pits/lands density is lower.
Also, in the real world, I guess spinning the disc faster increases vibrations or something mechanical like that and errors happen more often.
nocash wrote: September 1st, 2023, 6:44 pm I can't even find a simple drawing, like those in the playstation pdf patent file.
We can find these pictures of blank (b) and recorded (c) CD-R under a SEM:
CD-R under SEM.png
It's from this paper:
A simple experiment to distinguish between replicated and duplicated compact discs using Fraunhofer diffraction.pdf
Obviously, the schematic on the patent is exaggerating how the wobble looks like. In real life, the tracks are way more straight. But still, that's kind of amazing the electronics are able to get that weak wobble.
nocash wrote: September 1st, 2023, 6:44 pm As far as I understand, the 22kHz wobble is everywhere on CDRs (as timing mark), and there's some kind of additional wobbling for ATIP bits? Or are they using absence of wobbling for ATIP bits, similar as for the SCEx bits?
The wobble itself (22kHz sine wave) is everywhere to regulate the spindle speed while burning.
But it is also frequency-modulated to carry the ATIP frames. You should check the ECMA-394 standard PDF, everything is documented on the ATIP.
nocash wrote: September 1st, 2023, 6:44 pm How much do you need to increase the rotation speed?
In the video, the disc spins at around 1.5x faster meaning that the 22kHz is at 35kHz.
I would say aiming the 32-36kHz range is the best. I could go to 2x faster (equivalent 4x speed in 2x mode) but it begins to be scary and not really useful I believe.

I tried to lower the speed by making shorter pits/lands but I couldn't go as lower as I wanted.
Also, because the pattern is made by burning basically 100x longer pits/lands, the disc wanted to speed up a bit and the original 22kHz was detected again.
nocash wrote: September 1st, 2023, 6:44 pm Would it be possible to filter-out the 22kHz tracking error wobble, so the drive would simply ignore it?
Then you could perhaps burn a straight line (and apply your own SCEx wobble where needed, or disable the filter in that places).
That might work even when using normal rotation speed (hoping that the burned signal would override the original pre-groove wobble).
I tried and that was a bit working but not enough. Making straight lines doesn't override the wobble. IIRC at the beginning the pattern was not really there, the original 22kHz was still detected then thanks to the continuous pits coding the 0 of the bitstream, the disc started to spin faster automatically (due to the reason mentioned earlier) and my pattern appeared but the tracking signal was almost constantly resetting not being able to recover useful data to decode.
Then I believe that's how I had the idea to increase the disc speed which was the only solution I could imagine to get rid of the original wobble. Also, by increasing it, the continuous pits were not needed anymore and the tracking was resetting less often.
nocash wrote: September 1st, 2023, 6:44 pm Btw. did you try the burned CDR on a console with modchip? Just in case you've accidently made the TOC reading or data reading unreliable, causing problems unrelated to SCEx reading.
Yes, I use a modchipped console where I can remove independently the SCEx and gate signals with jumpers.
The TOC reading is one of the issues I have currently. The pattern is destroying the lead-in data. So I have to find a trade-off to burn enough of it without overwriting too much data. If the TOC is read correctly, the drive will try to seek to leave the lead-in but too much pattern just makes seeking it around 20-30s backwards.
Sometimes, it's even worse because it seeks a few sectors before and it gets stuck, like in pause mode.
Then the disc may stop and the PS1 stays on the menu.

In the video, the lead-in in this disc is almost completely overwritten with the pattern, in the hope that the Q subchannel can still be read a few times to get the TOC which sometimes happen.
This shouldn't be an issue if we can inject the SCEx signal in the tracking coils directly while burning.
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Post by alexfree » September 2nd, 2023, 4:45 pm

nocash wrote: September 1st, 2023, 6:03 pm 1) I am quite sure that there are already modchips doing that, that's nothing new.
3) How on earth could the spindle speed affect the sled seek times??? Faster rotation is only needed in Lead-in, doing it elsewhere would cause issues on movie/audio streaming timings.
4) It's just a normal disc with SCEx, same as retail discs, it won't behave different if you open a door.
5) We have the patent, and mod chip source code, and this thread, more info isn't possible. At best, you could ask for less info.
1) What's new is it's on a disc. In theory say he could manage to get all three strings to work but it would be quite harder. If said idea works this way then you can have 2 versions of a disc that are completely universal on stock consoles.

Disc Version 1 would need the japanese license data. It would work on everything except the SCPH-102s.
Disc Version 2 would need the european license data. It would work on everything except SCPH-3000-SCPH-100 Japanese consoles.

3)I was kind of vague but I meant the overall speed increase causing data read reliability issues, longer read times, etc like his response states.

4) I think your missing the point I was trying to figure out. If these self-boot CD-Rs are constantly spinning faster and having worse data reads, it makes sense with the current limitations of this method to create a soft-mod self-boot CD-R that can then unlock the drive or do an artifical swap trick, so that you then can put in a normal CD-R (not using this method) and play games without the speed issue impacting anything.

5) A lot of this is going over my head but it is very interesting. I never got this low level into the CD technology.
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Post by alexfree » September 2nd, 2023, 4:57 pm

david4599 wrote: September 2nd, 2023, 11:37 am 1) Yep, I can literally burn almost any pattern but burning the 3 words will be even less reliable until I can find how to solve the other issues.

FYI, Datel did exactly that, here is a capture of the breaker pro I have (blue = tracking signal CL709 on PU-18, yellow and pink = SCEx signal and gate output where modchips wires are soldered to):
DS1Z_QuickPrint131.png

2) I have the printable datalifeplus AZO Verbatim but in lower quantity than these "extra protection" ones. For the wobble check, these discs seem fine but I'm still thinking to try the "Taiyo Yuden" ones.
I just checked and compared these disc types against the two 5502 I have and I can confirm that their drives (one original and one "made in china") are not great especially the old original one hence the reading issue in 2x mode in the video.

3) Yeah, the speed is increased everywhere. Right now, I'm working on trying to change the pits/lands length while burning by adjusing the laser speed setting thanks to the right DSP command.
It suprisingly kind of works, the PS1 auto-adjusts the spindle speed when recognizing different pits/lands length but a few sectors can't be decoded if the change is too sudden. I guess I have to do smaller steps.

4) This wouldn't be useful if I can manage what I said just before, but why not. Yep, the swapped discs will spin at normal speed since their pits/lands length is normal.

5) Like the former Datel engineer says in the comment, it's just the 22kHz sine wave normally used for CD-R/RW that will be switched on and off accordingly to the SCEx bitstream.
Now, if you mean how my pattern creates it, basically I'm overwriting existing data with huge pits, the photodiodes of the drive just receive less (or more?) light every 23us (half a period of 22kHz).
This will produce a voltage change every 23us in the resulting tracking signal that the 22kHz filter of the PS1 (made specifically for the SCEx wobble detection) is able to see.
nocash wrote: September 1st, 2023, 6:03 pm Faster rotation is only needed in Lead-in, doing it elsewhere would cause issues on movie/audio streaming timings.
A CD player is searching for the good pits/lands frequency and will automatically adapt the spindle speed (CLV mode). If the pits/lands are burned longer, the player will just increase the speed and the bitrate will stay the same (176kbps in 1x and 353kbps in 2x), musics and movies timings won't change. The donwnside is that the disc can hold less information since the pits/lands density is lower.
Also, in the real world, I guess spinning the disc faster increases vibrations or something mechanical like that and errors happen more often.
nocash wrote: September 1st, 2023, 6:44 pm I can't even find a simple drawing, like those in the playstation pdf patent file.
We can find these pictures of blank (b) and recorded (c) CD-R under a SEM:
CD-R under SEM.png

It's from this paper:
A simple experiment to distinguish between replicated and duplicated compact discs using Fraunhofer diffraction.pdf

Obviously, the schematic on the patent is exaggerating how the wobble looks like. In real life, the tracks are way more straight. But still, that's kind of amazing the electronics are able to get that weak wobble.
nocash wrote: September 1st, 2023, 6:44 pm As far as I understand, the 22kHz wobble is everywhere on CDRs (as timing mark), and there's some kind of additional wobbling for ATIP bits? Or are they using absence of wobbling for ATIP bits, similar as for the SCEx bits?
The wobble itself (22kHz sine wave) is everywhere to regulate the spindle speed while burning.
But it is also frequency-modulated to carry the ATIP frames. You should check the ECMA-394 standard PDF, everything is documented on the ATIP.
nocash wrote: September 1st, 2023, 6:44 pm How much do you need to increase the rotation speed?
In the video, the disc spins at around 1.5x faster meaning that the 22kHz is at 35kHz.
I would say aiming the 32-36kHz range is the best. I could go to 2x faster (equivalent 4x speed in 2x mode) but it begins to be scary and not really useful I believe.

I tried to lower the speed by making shorter pits/lands but I couldn't go as lower as I wanted.
Also, because the pattern is made by burning basically 100x longer pits/lands, the disc wanted to speed up a bit and the original 22kHz was detected again.
nocash wrote: September 1st, 2023, 6:44 pm Would it be possible to filter-out the 22kHz tracking error wobble, so the drive would simply ignore it?
Then you could perhaps burn a straight line (and apply your own SCEx wobble where needed, or disable the filter in that places).
That might work even when using normal rotation speed (hoping that the burned signal would override the original pre-groove wobble).
I tried and that was a bit working but not enough. Making straight lines doesn't override the wobble. IIRC at the beginning the pattern was not really there, the original 22kHz was still detected then thanks to the continuous pits coding the 0 of the bitstream, the disc started to spin faster automatically (due to the reason mentioned earlier) and my pattern appeared but the tracking signal was almost constantly resetting not being able to recover useful data to decode.
Then I believe that's how I had the idea to increase the disc speed which was the only solution I could imagine to get rid of the original wobble. Also, by increasing it, the continuous pits were not needed anymore and the tracking was resetting less often.
nocash wrote: September 1st, 2023, 6:44 pm Btw. did you try the burned CDR on a console with modchip? Just in case you've accidently made the TOC reading or data reading unreliable, causing problems unrelated to SCEx reading.
Yes, I use a modchipped console where I can remove independently the SCEx and gate signals with jumpers.
The TOC reading is one of the issues I have currently. The pattern is destroying the lead-in data. So I have to find a trade-off to burn enough of it without overwriting too much data. If the TOC is read correctly, the drive will try to seek to leave the lead-in but too much pattern just makes seeking it around 20-30s backwards.
Sometimes, it's even worse because it seeks a few sectors before and it gets stuck, like in pause mode.
Then the disc may stop and the PS1 stays on the menu.

In the video, the lead-in in this disc is almost completely overwritten with the pattern, in the hope that the Q subchannel can still be read a few times to get the TOC which sometimes happen.
This shouldn't be an issue if we can inject the SCEx signal in the tracking coils directly while burning.
Thank you very much for answering everything. I can not wait for the blog posts and to create my own self-booting CD-Rs! About your drives, the 'made in china' ones were confirmed by shadow here on psxdev to not be anything more then poorly done refurbished original units IIRC.

I would definitely try to re lubricate the drives as per: https://alex-free.github.io/unofficial- ... ce-manual/ . I also wonder if reliability on reading the SCEX wobble would increase on the earlier models using the analog servo? That would be all the pre auto BIAS/GAIN models.

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