Request: DOS Support; + Audio CD

[hjnijlunsing]

One use case where this appliance would shine would be DOS support.
Unfortunately I have not been able to make this work (https://www.bootdisk.com/usb.htm)

This would give retro gamers the possibility to switch game cd's without having a real optical drive.
Should this be working?

Another thing I would imagine which might be useful is Audio CD support (also for dos gaming); would it be possible to intercept the play track commands to the virtual USB CDROM, and play FLAC/MP3 based on trackxx.wav on the Raspberry PI; Thus I am thinking Pi-Zero -> HDMI -> HDMIAudio Extractor -> CD AUDIO

[hjnijlunsing]

Ok, it actually seems to work on systems. I was able to use this as a USB CDROM in DOS on a VIA board.
(Managed to get Red Alert working; Allies CD; 11th hour Install went fine but froze after starting the game)
However, switching CD's in DOS causes failures and not able to recognize the CD anymore.

Would it be possible to switch CD's in DOS?

[nistvan86]

The problem I think is that the shell scripts handling the image swap in the background are just loading/unloading the g_mass_storage kernel driver of Linux. This is responsible for the USB device emulation. So in view of the host PC it's like unplugging and replugging a real CD ROM drive by it's USB cable. That's not going to work under DOS with the BIOS USB CD routines.

There seems to be mentions in the kernel's MSG gadget documentation that replacing the media inside the emulated CD-ROM drive would be possible, if the drive is defined as "removable". The new backing file can be defined through the gadget's sysfs entry.

I'm currently playing with a VIA thin client trying to use it for retro gaming purposes, so I might eventually give this a try.
CD Audio would be an interesting addition, though I'm not sure the gadget kernel module sends the SCSI commands responsible for audio playback anywhere at the moment. There's a mention in the module source code that the current module only emulates a CD with a single data track.

[danifunker]

I figured out DOS CD Swapping in my project (usbode) by leveraging f_mass_storage kernel instead of g_mass_storage through configfs. I’m still trying to figure out audio though.