Feature request: allow disc images > 1024 cylinders

[rhalkyard]

It appears that by default, disc images are forced to conform to ADFS' 1024 cylinder limit when they are loaded. However some filesystems (e.g. ZIDEFS with the ICS card, or Armstrong Walker IDEFS with the HCCS A3000 card in PR #47) support multiple ADFS volumes on a larger, partitioned disc.

I modified these limits in my own build of Arculator, and it seems to function as expected - with my HCCS emulation, I can carve a 2GB image up into 4 512MB partitions, like I do with a flash disc on my real A3000. Given that this is a valid use case on original hardware, would it make sense to lift these limits, or at least add an "I know this is too big for ADFS and I want it anyway" option to bypass them?

[IJeffray]

Well, ZIDEFS does not "support multiple ADFS volumes" - it supports multiple IDE targets, each with a partitioning scheme which supports up to four Filecore logical drives. Not ADFS. ADFS is not Filecore. This distinction may be important if the original intent was to be strict about ADFS's limitations - notwithstanding that RISC OS 3.1's ADFS can actually handle physical media > 512MB, though only address the first 512MB of it -- not sure about anything before RISC OS 3.1.

[alexoughton]

For anyone else still dealing with this, I've learned a couple of things which may help you:

1. The 1024 cylinder limit appears to only apply to the GUI. I manually edited a machine config file to the correct number of cylinders and it seemed to work just fine.

2. An image file with bad permissions will look like a non-responsive drive in the emulator. I forgot to change ownership of my image file after sudo dd if=... generated it with root-ownership. No error is surfaced in the GUI or in the terminal output, the drive just doesn't respond within the emulator. Correcting ownership on the file will bring it to life.

3. At least under Linux, the emulator appears to work with direct access to a physical Compact Flash card. I manually edited my machine config file to point at /dev/sdd (instead of an image file), and it worked. For the same reason as point (2), this will either require running the emulator with sudo, or adding your user to the disk group (or whichever group owns the block device on your system). Finally, I edited my config file to use the symlink under /dev/disk/by-id for my Compact Flash reader, just in case it's not on /dev/sdd in the future.