Hello Levente, Ruud Levente> I'm with the idea of using an 1541 wreck and use the digital board, the Levente> PS and the case for the hdd. You can expand the original board with RAM, Levente> ROM and a portchip easily (if needed), you can keep all 1541 properties. Levente> So you can make your business about 99.99% compatible to the original Levente> 1541, even using the HDD instead of the floppies. I disagree with 99.9% compatibility. As most fasloaders directly reads/writes $1c01 and decodes GCR bytes bypassing DOS routines, the above mentioned thing simply wouldn't work. With specialized hw GCR coders/decoders or without you need an extra (micro)controller to drive HDD, convert data into GCR and transfer to $1c01 register. And not to mention head stepping :-))) Levente> Since it's just a hacked 1541, it works with all computers supporting Levente> the serial IEC bus. Like CMD units :-) Slow but compatible. Levente> Talking about the filesystem: I'd use a FAT-like system, just to make Levente> things easier. Maybe, I'd use a FAT-32 like stuff because of the many Levente> and small files. Compatibility with other file system has a non obvious advantage. Namely when FAT crashes there is some chance recover it with programs. Levente> Or you can decide with the CBM like scheme, to allocate a big Levente> bitmap on the first blocks of the HDD as BAM and use daisy-chain linked Levente> file blocks. It is much reliable even if BAM would crash somewhere. Levente> Of course, any old programs supporting direct block read/write commands Levente> would go mad when applying onto this filesystem. However, you have the Levente> option to treat special filetypes (regular 1541 disk images) on the HDD Levente> as subdirs too. When being able to not just copy, but even CD to an image Levente> file, your DOS can emulate a normal 1541 disk (as long as you're in the Levente> image), all with the appropriate parameters, Disk images *must* be supported and no way as 64NET system does (extracting files from disk). Levente> even low-level things like GCR codes. With some extra hw will do. Levente> Because of the image files, it would be possible to use not just 1541 Levente> but any type and kind of C= floppy images. Definately possible. There are plenty space even in the 1581 ROM. Levente> (Of course, it would be also a question of an at least 32K Eprom Levente> replacing the original, then all of your routines could reside in the Levente> expanded area (instead of scratching anything from the original DOS). Levente> There is fortunately, no problems with this extension, as there is fairly Levente> enough place to use in the memory map). Right. Ruud>Enough to place extra RAM as well. Can be used for a lot of purposes: Ruud>buffers, patches etc... Extra RAM also possible and I can't imagine without it. Ruud>I have to concentrate on the HW around the hD for the moment. This wil Ruud>include interfacing it with the 1541. Ruud>What has to be done as well is: Ruud>- Find out to direct the original routines to our own. This needs a good Ruud> knowledge of the original OS which I lack. I see no problem in this. There are plenty of commented 1541 ROM disassemblies. Ruud>- We have to implement our own commands (like CD, MKDIR etc) so we'll need Ruud> to know where to insert them in one or another way. This also not a big problem. Ruud>- Then the whole filesystem handling itself. It should be able of Ruud> handling/emulating more then one drive, subdirectories and dealing with Ruud> images. Here we can use the knowledge I've build up by programming Ruud> PC-Disk3. More RAM and ROM will help in that problem. Ruud>The way to program it: Ruud>- it must be in assembler. Ruud>- I'm thinking of using a "jump"-table. If we have to break in the original Ruud> OS, we first jump to this jump-table and from there to the new routine. Ruud> I think the advantages of a jump-table ore obvious. In the original ROM there are some jump table (in 1581 even more). Don't forget guys, that I having deal with 1541 near every day expanding and implementing new commands into my own 15xx emulator (I still work on it). Frank - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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