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@@ -1,203 +0,0 @@ - - - -Q: What is this tools aimed at anyway? -A: It is designed to handle ISO images you make from CDs. - - -Q: What is an ISO image anyway? -A: You can create an ISO with free tools like cdrdao in raw mode, or others, - like cdrwin, CloneCD, etc... - - -Q: Are all the ISO formats handled? -A: No. Only raw-2532 images files. Always the file format outputted by CloneCD - and cdrwin, and the format outputted by cdrdao with the --read-raw option. - - -Q: Is Nero's file format supported? -A: No. - - -Q: Why? Nero's a spreaded software! -A: It's a commercial tool. Since I don't use any commercial tool, and that no - free-software generates Nero ISO, it won't be suppored. - - -Q: What is this tool/library able to? -A: First, you can read/write sectors from/to an iso file. You can also read - informations about an iso file. You can extract/insert files from/to - an iso file. Depending upon the mode you'll be using, it will compute - the right CRC/ECC code for the given sector. The whole in the following - (eventually mixed) modes: MODE_1, MODE_2, MODE_2_FORM_1, MODE_2_FORM_2. - Additionnaly, it is able to produce patches (.ppf files) instead modifying - the iso file, saving you time when you use the right softwares. - Actually, it is quite "oriented" on the MODE_2* formats, since it's - the PSX's formats. - - -Q: I've heard CDmage or ECCRegen can also correct the sectors for me. -A: Maybe. Since it only runs on Win32 platforms, I've never tried it. - - -Q: So, what is the goal of this software? -A: To modify (patch) ISO images. Nothing else. And of course I want it free, - opensource, and working on my preffered operating system, Linux. If somebody - can make it working for windows (and I think this is easy to do) I will - please me. I can't do it right now since I don't really have the opportunity - to build Win32 binaries (apart of cygwin's ones) - - -Q: Where does the source code for the CRC/ECC comes from? -A: Originally, it has been taken from cdrdao. Yazoo has given some - modifications to it. Then I've cleaned it up and made some minor - modifications on my self. The source code was called 'yazedc'. - - -Q: Do you have the right to do so? -A: The software is GPL'ed. I've got the right to give modified versions - of it, as long as I don't claim the modificated thing it the original, - and as long as I mantion the original authors in it. - - -Q: What a strange name, 'yazedc' ? -A: I've got my own ideas about the name's origin... The easy solution: - "YAZoo EDC", where EDC is the field name of one of the things it will - recompute. But there is a more... complicated solution I won't give. - - -Q: So, I can modify your code too, create a new tool, and diffuse it? -A: Yes, as long as you give the full source code, that the new software - is also GPL'ed, and that you mantion me as the original writer of the - software, you can. Read the GPL carefully, it's very interesting. - - -Q: What is exactly the format of a CD-Rom? -A: Firstly, when you have a raw sector, you have to understand its primary form. - Secondly, the whole CD has an internal format, called the iso9660. The format - of the iso9660 is easy to find on the internet. Here is one first easy link: - http://www.ccs.neu.edu/home/bchafy/cdb/info/iso9660.txt - Then you have two more difficult documents: - http://www.ecma.ch/ecma1/stand/ecma-119.htm - and - http://www.ecma.ch/ecma1/stand/ecma-130.htm - - All those links were taken from the page - http://www.ccs.neu.edu/home/bchafy/cdb/info/info.html - - The sector format is a bit complicated to find on the internet. Here is what - I've found. - - First you have to know that there is many formats that describe the sector's - organisation. Those are called "Books". There is the Red Book, the Yellow - Book, the Blue Book, the Green Book, the Orange Book, and the White Book. - - The Red Book is for Audio CD. The Yellow for common CD-Roms. The Blue book - for Philips's VideoCD. The Green Book for CD-i and CD-XA. The Orange Book - for CD-R cds. And the White Book seems to be a replacement of the Green one. - - This is quite unclear and you have to actually buy the books since they - aren't in public domain. - - So the informations I'll give comes from various source of various free - softwares. Should I mention two: cdrdao http://cdrdao.sourceforge.net - and ECCRegen http://web.tiscali.it/eccregen as the most useful sources. - - Here is the general form of a CD-Rom sector: - - <--------------------------- sector: 2352 bytes ------------------------------> - <- Header: 16 bytes -><---------------- Datas: 2336 bytes --------------------> - - Let's move to the header description: - - <--------------------------- header: 16 bytes ------------------------------> - <-- sync bytes: 12 bytes --><-- localisation: 3 bytes --><-- mode: 1 byte --> - - The sync bytes are easy: it is always 00 FF FF FF FF FF FF FF FF FF FF 00 - - The localisation is the sector "position" described in time. For example, - the sector 200000 of a CD is at the "time" 44:28:50. The first is the number - of minutes, the second is the number of seconds, in the range 0-59 and the - last is the frame number, in the range 0-74. It means there is 75 frames - into a second for a CD player. Please note that the CD "begins" at 00:02:00. - - Ok now that we know all this, you can feel the way the localisation is - stored. But it is not that easy... - - <-------------------- localisation: 3 bytes --------------------> - <-- minute: 1 byte --><-- second: 1 byte --><-- frame: 1 byte --> - - That's seems to be all right *BUT* the fact is that the bytes are stored - in packed BCD format. You may know what the BCD format is if you are "old" - enough for that. I won't enter into the details so if you want a more - description of the BCD format, look into the net. You only have to know that: - -unsigned char from_BCD(unsigned char x) {return ((x & 15) + (x & 240) * 10));} -unsigned char to_BCD(unsigned char x) {return ((x / 10) << 4) | (x % 10));} -int is_valid_BCD(unsigned char x) {return (((x & 15) < 10) && ((x >> 4) < 10));} - - Last thing: when you look at a BCD packed number, you have to read it in - hexadecimal, and then you will see a "decimal" number. So when you count - in BCD, you'll have this: 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, - 0x08, 0x09, 0x10, 0x11, 0x12, etc... You see? You've got a "gap": no 0x0a, - 0x0b, 0x0c, etc... So the BCD is only a trick for an easy reading of hexa - dumps of various informations. - - All right. This was for the localisation part. The last part is the mode - byte. It is really simple actually. It is 0 for an empty sector, 1 for a - sector in MODE1, and 2 for a sector in MODE2. Easy as hell. - - Ok here we are: we know the basic form of a CD's sector, and even know the - MODE of the sector. Now the datas depends upon the sector mode. Here you have - the various kinds: - - <-------------- MODE 1 FORM 1 Sector datas: 2336 bytes ----------------------> - <- datas: 2048 bytes -><- EDC: 4 bytes -><- 0s: 8 bytes -><- ECC: 276 bytes -> - - <---------- MODE 1 FORM 2 and also MODE 2 Sector datas: 2336 bytes ----------> - <----------------------------- datas: 2336 bytes ----------------------------> - - <-------------- MODE 2 FORM 1 Sector datas: 2336 bytes ----------------------> - <- SH: 8 bytes -><- datas: 2048 bytes -><- EDC: 4 bytes -><- ECC: 276 bytes -> - - <-------------- MODE 2 FORM 2 Sector datas: 2336 bytes ----------------------> - <- SH: 8 bytes -><---------- datas: 2324 bytes ----------><- spare: 4 bytes -> - - Well, I *really* don't know how to distinguish the different "FORMS" from - each others for the MODE 1. Have to look further for this. - - The ECC and EDC controls blocks. The yazedc code can compute them, so - don't worry about them. - - The 'SH' (SubHeader) field is the most "complicated" one. Those eight little - bits are the only one I'm really not sure of. All of that because you have to - buy the Books to find the information. This SubHeader is only found into - MODE_2_FORM_1 and MODE_2_FORM_2 sectors. - - Here you have the informations I've been able to gather: - - -) The SubHeader has 8 bytes, but it's twice the same 4 bytes. - -) The 4 bytes are described using the following fields: - o) 1st byte: File Number (FN) - o) 2nd byte: Channel Number (CN) - o) 3rd byte: Sub Mode (SM) - o) 4st byte: Coding Info (CI) - -) I've *never* seen any SubHeader with a FN, CN or CI different from 0, - please inform me if you do. - -) The Sub Mode byte is a bit field which seems to be described like this: - 0: End of Record (EOR) - 1: Video - 2: Audio - 3: Data - 4: Trigger - 5: Form 2 - 6: Real Time (RT) - 7: End of File (EOF) - - Very last things to know: of course, the PSX has the CDs in MODE 2... So the - common files are stored in MODE 2 FORM 1, the STR/XA files are stored in - MODE 2 and I've never seen any file stored in MODE 2 FORM 2. And the MODE 2 - FORM 1 and MODE 2 FORM 2 are also called XA-Mode1 and XA-Mode2 or simplier: - XA-1 and XA-2. - - I hope this will help you as it helped me writing this software. |