Many problem disks have been reverse-engineered to discover why they didn’t work. A few required emulator enhancements to improve hardware accuracy, but most were missing details from the original disks, due to some creative floppy controller use by the copy protection checks. Not all of these could be supported by the original EDSK specification.

Back in October 2005, I suggested a few EDSK enhancements, designed to address some known limitations of the format. The extensions didn’t involve anything too radical, to maintain as much backwards compatibility as possible.

It’s now three years later, and a number of new gap-related CPC protections have been identified, which are beyond the scope of even the extended Extended DSK format! I’ve made further changes to address the new requirements, as well as a correction to a previous one.

My development version of SAMdisk includes support for all the new features, and will be released if the extensions are approved. Other programs will need similar enhancements to take advantage of them, particularly emulators wanting to run some of the difficult disks.

See the updated extensions document for further details. There are also sample disk images showing each extension.

The new interface is a simplified version of the original Atom HDD interface, and is now primarily for Compact Flash use. The Atom Lite uses an ATA feature for 8-bit data accesses, rather than normal 16-bit IDE mode, avoiding the need for half the data to be latched inside the interface. The change simplifies the design and allows faster data transfers – the next data byte is now fetched with a single IN, rather than having to select the high or (latched) low address first. Streamed media playback anyone?

The new interface requires updated B-DOS and HD-BOOT ROM versions to select 8-bit mode, but once set it’s software compatible with the original interface. Data can be read from both &F6 and &F7 ports as before, despite no latching being involved this time. However, the change does means the byte order of the Atom Lite media is reversed (or perhaps un-reversed!) compared to the Atom, which returned the high byte first. Fear not, existing Atom media can be converted to use Atom Lite byte-order using SamDisk!

The changes to SimCoupe were mainly to the ATA emulation, with enhancements to support 8-bit data mode and 28-bit LBA sector addressing. The latter allows support for devices beyond the 8GB CHS limit (16383 cylinders, 16 heads, 63 sectors), extending the maximum size to a whopping 137GB. Even an 8GB card would contain almost 10,000 B-DOS records, which could easily contain every SAM software title ever written! The Atom Lite implementation is just a cut-down version of the existing Atom C++ class, which has been further simplified as part of the same changes.

The SamDisk changes were also fairly trivial, especially as there’s no ATA emulation to worry about. The byte order of the media is determined by examining the BDOS signature at offset 0xe8 in the first record (which follows the boot sector and record list). With the original Atom (seen as “DBSO”) data accesses must be byte-swapped after reads and before writes. This allows all record-level commands to work transparently on both media. A new command-line option (/bs) forces byte-swapping of entire images, used for the Atom <-> Atom Lite conversion mentioned above. Simply read the device to an HDF image using the byte-swap option, then write the converted image back to the original device.

The Atom Lite 2.x boards are expected to include a Dallas clock chip, with registers access through the same floppy 2 ports. SimCoupe support will be added once the details have been confirmed…

1. fdrawcmd.sys is almost unchanged since the 1.0.1.9 release in May, as there’s been nothing much to do. I’ve no outstanding issues to fix, and only a minor enhancement that wasn’t worth a new release.

   I’ve been working on improving the driver installer, which will use the same NSIS setup as SimCoupe instead of my small custom installer. This will give a more traditional install/uninstall process and include both 32-bit and 64-bit drivers in one download. I’ll release a new version once it is complete, even if the embedded drivers don’t get updated from the previous release.

2. SimCoupe is also due a refresh build in the next month, mainly to improve Vista support. I’ve done some minor enhancements and fixes to the main code branch, but only enough to make it version 1.01 rather than 1.1.

   I’ve made a start to bigger changes in a code branch, which largely involves separating the emulation+sound from the UI+video processing. This should hopefully eliminate the occasional sound glitches from moving things over the main window, etc. It should also do more to spread the workload on multi-core CPUs. I also have some fragments of other features, including movie and sound recording.

3. SamDisk has been neglected for a few months, despite having been close to a release for a while! I’m happy with the core functionality, which does an excellent job with copy-protected and custom formatted disks (right to the limit of the PC controller’s ability). I’ve still not decided on the list of disk image formats for the initial version, but it’ll certainly include EDSK, MGT, TRD, D81 and BPB (for normal PC disks).