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Text File | 2007-01-01 | 10.7 KB | 369 lines

u The 6502-RAMROM as drive expander Part 2 ============================== i Wolfgang Moser and Nicolas Welte Now, with the patched ROMs, I was able to Flash other ROM banks without the need to switch back to the original CBM DOS 2.6 ROM (which worked flawlessly with all previous tests). Problems with the prototype another problem manifested when analyzing the [store-to-ROMk problem with the drive expansion 6502-RAMROM prototype What happens, when someone wants to flash the whole ROM, but the DD2 RAM configuration is selected? Because the DD2 RAM overlays the drive's address space from 0x8000 to 0x9FFF the Flash-ROM cannot be addressed there. Furthermore, DD2 went crazy, whenever the Flash enable switch was set. Nicolas detected the problem by carefully reviewing the 1541 GAL equations. The Flash option switch disables the overlaying RAM for write operations. Not a big task, because only the GAL needs to be replaced, I thought. First we decided to patch the floppy DOS ROM part of Dolphin-DOS 2.0. The ROM code should not access the 8kB RAM at the memory address location 0x8000...0x9FFF anymore, but at the addresses 0x6000...0x7FFF. That way no changes to the 6502-RAMROM would needed, because the RAMboard configuration could be used instead. And flashing the full 32kB ROM bank should become possible, too. But Nicolas reported, that the patched DD2-6 ROM didn't work, although other tests with the VICE emulator showed no problems. He found out, that there was a real hardware problem, that depends on the special address decoding behaviour of the CBM drive series (RAM and especially VIA locations mirrored at different addresses; IRQ flag handling). Since the PET and VIC20 computers don't contain such mirrored device address spaces, this problem couldn't be detected with the PET/VIC20 6502-RAMROM prototypes. The Solution Nicolas worked out a solution, that needed the least possible changes to the PCB in combination with changed GAL equations. Without the GAL, this fix would have been a huge patch orgy. Unfortunately you have to redo the patch if you want to use the 6502-RAMROM in a VIC20 or PET again. Although not needed I installed some jumpers to easily configure the PCB for both options. In the meantime I tested flashing other Flash-ROMs with different sizes. I had an AT29C020 as spare and tested the bigger flashing page size. Reading out the ROM contents with the c't-Flasher at my PC again showed no differences. Note: you can't access/flash half of the banks of this ROM type without further hardware modifications. Then I tested an AT29C256 as a small replacement for my C64 Kernal switch board. [AT29C256 to 32 pin Flash-Adaptor, bottom view, [AT29C256 to 32 pin Flash-Adaptor, top view, Before I had to build a small Flash adaptor, because the 29C256 has got a different pinout (28 pins) than the standard 32 pin Flash ROM chips. I hacked Nicolas' Flash-ROM board a little bit by cutting some traces. Although the Flash-ROM PCB was not designed for this purpose it fitted my needs best (instead of building a cable wired adaptor). Flashing the 29C256 with the least possible page size brought me a very small kernal switch board in a few minutes; thanks to the well designed Flasher software , that is able to burn different parts of the ROM chip in several steps (by selecting a start address of 0x8000, 0xA000, 0xC000 or 0xE000). 6502-RAMROM final release test report from Womo, 2003-02-16 Retesting different flashing scenarios to check, that the problems with Dolphin-DOS were gone After I got the new changed GALs I repeated all the earlier tests: Flashing the original CBM DOS V2.6 into bank 0 Selecting bank 0 and flashing the patched SpeedDOS 40 tracks ROM into bank 1 Selecting bank 1 and flashing the original Dolphin-DOS 2.0 ROM into bank 2. Because of the applied SpeedDOS ROM patch, the Flash procedure went flawlessly. Selecting bank 2, configuring the DD2 RAM configuration and flashing the patched Dolphin-DOS-2.0-6 ROM (RAM a location 0x6000 to 0x7FFF) into bank 3. No problems with that and it shows, that you can now Flash the ROM locations from 0xA000 to 0xFFFF, when the original Dolphin-DOS 2.0 is enabled. But don't try to Flash the ROM location at 0x8000. Because it is used by DD2's RAM, the drive may become stubborn. Selecting bank 3, configuring the RAM-Board configuration and flashing the Dolphin-DOS 3.0 ROM into bank 0. With the patched DD2-6 ROM the full ROM bank (0x8000 to 0xFFFF) could be flashed without any problem, thanks to the hardware modification and the new GAL. After preparing some matching C64 Kernal ROMs [AT29C256 to C64 Kernaladaptor, top view, [AT29C256 to C64 Kernaladaptor, bottom view,] I started testing the burned SpeedDOS and Dolphin-DOS versions. As mentioned earlier the patched SpeedDOS and also the original Dolphin-DOS ROM worked without problems. I also tested some special Dolphin-DOS copy programs (Dolphin-Copy) without problems. The patched Dolphin-DOS-2.0-6 (RAM at 0x6000) is another task, with this ROM, the Dolphin-Copy program doesn't work, because the RAM location seems to be hardcoded into the copy tool. I also tested Dolphin-DOS 3.0, which worked fine with the exception that it was nearly as slow as the original CBM DOS. No wonder, because DD3 makes use of an extra parallel port chip (6821 PIA) within the drive. It cannot communicate over the standard parallel port cable connected to the VIA 6522, therefore it has to use the slow serial bus transfer routines. The future and some ideas Until now, mainly the ROM part of the 6502-RAMROM was tested, in the future I'll have to look at the RAM configurations, especially in some applications for the maxRam-Mode. Perhaps Markus Brenner wants to jump in here and extends his Burstnibbler based transfer tool [mnibk , so that much more sophisticated copy protections can be dumped to G64 disk images. I already started analyzing the Dolphin-DOS 3.0 DOS ROM looking for all the parallel port accesses to the 6821 PIA. Maybe I'm able to patch it, so that it makes use of the VIA 6522 parallel port. This way people may use Dolphin-DOS 3.0 without hardware hacking; that means adding an additional 6821 PIA into the floppy. I should take my 1571 floppy drive sometime and test it with the 6502-RAMROM, too. There are other floppy speeders, especially designed for this drive. Not only to mention Dolphin-DOS 3.0 for the 1571, but especially Prospeed-1571. With this drive, the maxRam mode of the 6502-RAMROM cannot be used, it would overlay the 1571's CIA and the registers of the WD177x controller. It may be interesting what could happen, if the maxRam mode is used nevertheless. Not enough, there are more problems with the Commodore 1571 disk drive. Since there is incredibly little space between the mainboard and the transformer assembled over it, I currently don't know, how to insert the 6502-RAMROM into the 1571 drive best. One solution may be to connect the board with some flat cable to the processor socket. As for the parallel cable connector (1571 Burstnibbler cable compatible) I already built another lowest profile adaptor. [Inserted 1571 low profileparallel cable adaptor, [Space upon 1571 low profile parallel cable adaptor, [1571 low profile parallel cable adaptor, top view, [1571 low profile parallel cable adaptor, bottom view, Conclusion and application scenarios Speeder system [emulatork[Emulatingk different DOS ROMs and simple speeder systems like Jiffy-DOS, SpeedDOS or Dolphin-DOS is the playfield of the 6502-RAMROM, when inserted into Commdore's disk drives. You only need to add a simple parallel cable for some of these systems. Atmel Flash device programmer In combination with a patched Dolphin-DOS (DD2-6) , this hardware extends your floppy disk drive to a full blown high speed Atmel Flash device programmer. You will never need to handle with EPROMs and EPROM burners again. There is no need anymore for transfering the ROM files slowly to the computer memory before they can be written to the EPROM. The well designed flasher software makes your life even simpler. Maybe you want to replace your system ROMs with DD2-6, which requires some little hardware modification (using address line A14 for switching the upper and lower part of the DD2 ROM at 0xA000/0xE000); this way you can flash the whole chip. Nicolas is also working on more functions, like programmable bank switching about unused VIA/CIA port lines. Maybe not only Dolphin-DOS-2.0-6 can speed up the Flash process a little bit, but other drive speeders like Jiffy-DOS, too. Because of the special designed In-System-Flash software, the whole process is not really slow on a 1541 drive equipped with a standard CBM DOS (35 seconds for 32kB). So you don't need to install a speeder system or ROM in any case, instead it is an option. And Nicolas said, the Flash software contains some potential for speedups with the 1541 drive. Let's wait, test and see... RAM (only) expander (1541/1571 RAMBoard) and RAM diagnostic moduleMore applications of this board may rely on the RAM option only, you could save some money by not making use of the Flash-ROM chip. Copy software like the well known tool series Maverick already know how to use a RAMBoard equipped drive which the 6502-RAMROM can easily be configured to [emulatek. Perhaps Michael Klein (cbm4linux or other people may want to develop special software, that makes use of a maxRAM equipped disk drive (nearly 32kB of RAM usable). Not to mention the RAM diagnostic functionality that replaces the drive's builtin RAM by the one from the 6502-RAMROM. Things, the 6502-RAMROM can't do easily Because the hardware was mainly designed for universality and simplicity, it is not a general speeder system hardware emulator. Systems like Dolphin-DOS 3.0, Professional-DOS or Prologic-DOS cannot be used without further extensions or ROM patches. This purpose may be the job of another hardware extension board, one of the projects I am currently working on. Taken from the website http://d81.de/6502RamRom/ i Wolfgang Moser and Nicolas Welte Re printed with owners consent Notes From Wolfgang Moser on the project ==================================== Email: -Wolfgang Moser in general I agree about reprinting parts of my online article, if authorship is made clear and the origin of this article is named. Spelling corrections may be done. Then the article sometimes contains outdated informations, like e.g.: "Nicolas is also working on more functions, like programmable bank switching about unused VIA/CIA port lines." Nicolas is currently not working on extensions to the 6502-RamRom, it perfectly does its job as it is. Since Nicolas also may want to agree to reprint my article or because he wants to point out other things, he got a Bcc copy of this mail. Commodore Free I received no email from Nicolas but decided to print the article ...end...