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XT-FDC project level of interest

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    It seems like you are describing a ROM drive rather than a FDC. I think it is outside the scope of a robust FDC with BIOS.

    Accessing a large ROM would require some sort of paging mechanism like a latch to provide a small 8KB or 32KB "window" into the larger ROM (128KB or larger). It is certainly possible but sounds like another board project rather than something part of XT-FDC. As a result it is a more complex than decoding a simple small ROM and would require its own IO port and associated chips. Maybe that's a follow on project?

    Let's see what Chuck has to say. We are still working out how to store configuration data without risk of corrupting the BIOS.

    Thanks and have a nice day!

    Andrew Lynch


      It's an interesting idea, but I am in principle against taking up more memory space than absolutely necessary--and 64K is a lot of memory space. if you have other adapters requiring BIOS address space of their own. Generally speaking, any adapter shouldn't take more than 8K of space. If you were to do something like this, I'd recommend a serial flash device.

      But I think we're getting too far afield from the original intent--you really do have to rein in creeping featurism. If there were space left over in the ROM, I might see putting in a simple debugger so that one might be able to poke around a bit. But even that's not exactly on-mission.
      Reach me: vcfblackhole _at_ protonmail dot com.


        Originally posted by Chuck(G) View Post
        But I think we're getting too far afield from the original intent--you really do have to rein in creeping featurism. If there were space left over in the ROM, I might see putting in a simple debugger so that one might be able to poke around a bit. But even that's not exactly on-mission.
        This OS idea is a result of years being frustrated by bad boot disks . But I did get your point, the project is a FDC controller, not a problem solver.


          I would keep the idea in mind for after the XT-FDC project. Maybe the XT-ROM project? An 8 bit ISA board withan 8KB BIOS and an 8KB window into 512KB Flash ROM. That would be a doable project. Basically the computer would boot to a ROM drive rather than a floppy or IDE device. Ironically the N8VEM SBC does this already with CP/M 2.2 and it works great. It is a good idea for its own board!

          Thanks and have a nice day!

          Andrew Lynch


            Originally posted by lucasdaytona View Post
            This OS idea is a result of years being frustrated by bad boot disks . But I did get your point, the project is a FDC controller, not a problem solver.

            Do take a look at James' XT-CF project. With the CF accessible through the rear bracket, I can think of no easier sneakernet application that dropping everything on a CF card using another computer and plugging it in.
            Reach me: vcfblackhole _at_ protonmail dot com.


              On a FDC ROM only added applications i can imagine would be Fdisk, and some sub routines that would increase throughput without increasing overhead.


                I'm confused by the discussions of boot menus, built in programs, etc.

                This is a floppy drive controller. The BIOS for it should be pretty much a replacement of the on-board floppy controller routines, with some additional BIOS level functions.

                The XT-IDE (and other hard drive controllers) can include boot menus and low-level utility programs because they have BIOSes that are detected by the scan at boot time. This FDC replacement BIOS at boot time will probably just replace the FDC related interrupt vectors installed by the default BIOS. Anything else (boot menus for example) seems like asking for trouble by creating conflicts with existing SCSI and hard drive controllers.

                If you start talking about including programs like FDISK, then the question comes up - which version? And what does FDISK have to do with a floppy controller?

                Am I missing something?



                  Well what i mean is we need just that small extra like low level formatting, or a disk checker/header alignment, This can be resided in the ROM.
                  Even more so it doesn't need to be big, it needs to simply work.
                  We shouldn't depend in this case on Disk depending software since there might be trouble with the hardware.
                  So I do not feel like asking for a boot menu but I do ask for utilities to check the FDC itself and the connected FDD's.


                    If it wasn't too complex I would certainly recommend SD or CF reader for disk images. I'm not sure how much that complicates the design or again perhaps that's left best in another project but I would think it would extremely convenient with the availability of working physical drives starting to wane. If I could just pop a card into an 8-bit IBM compatible system and boot it off an image I found via sd or some currently available media that would speed life right along including the ability then to try and clone images back to physical media or visa verse.
                    Looking to acquire: IBM 5100, Altair 8800


                      Problem with CF or SD is SD requires a USB interface as far as I know (are there any SD controllers that don't run on USB that aren't surface mount?) or USB or IDE for CF.


                        SD doesn't require USB and can be implemented with a uC or simple latches. This would not be hard to implement either. On N8VEM we do this on the PPISD and the N8. SD is pretty simple to implement a bare bones implementation. I think it is out of scope for XT-FDC though.

                        An ISA SD board does make some sense but not combined with the XT-FDC. Those are two different concepts and we would be better served with two distinct boards. Also there isn't any commonality in the circuitry between the two functions so you'd placing two boards worth of parts on one PCB which just makes it more expensive and appealing to fewer people. Keep the idea as a follow on though since it is worth revisiting.

                        Thanks and have a nice day!

                        Andrew Lynch


                          For SD card i usually make use of a shifter.
                          Oh do remember to have a 8 bit D-latch to compare for data integrity.

                          I have to Agree with Andrew it is not the same as a FDC and is a whole different beast.(Perhaps a future project?)


                            I think that would be a better idea to open this discussion (ROM boot) on another thread, sorry for bringing it here, let's focus on the XT-FDC.

                            A FDC that supports low and high density drives is already very awesome!


                              I think you guys are requesting features a lot more complicated than this project is looking for, a simple HD floppy controller. I think the efforts should be in a way to keep component count the lower possible, and the BIOS the simpler implementation. Reading floppy images from SD or CF cards or emulating a floppy drive using a EPROM and booting from it seem for me unnecessary tasks having the wonderful XT-IDE installed.
                              My videos:
                              IBM PS/1 model 2011 restored and enhanced
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                                $160 for 4 boards??? How big are they? How many layers? Sounds kinda steep...