After reading the entire thread I put together the quotes I found most useful..
Well... what can I say, probably *all* USB Display Adapters use the same kind of chipset: The DisplayLink DL-120 or DL-160 (latter has the higher resolutions). I opened the box and the thing consists of only three chips. The very fat ASIC BGA DL-120, a DVI encoder chip and 16MB of DDR memory. 16 MB, seems a lot for an adapter that can only display 1280x1024 in 24 bit. But then again, it surely has at least two frame buffers (double buffering) to avoid tearing effects and probably a rather large decompression buffer for the compressed data. The device only has one bulk output with 512 bytes per packet and on interrupt in endpoint. The rest is done via control transfers.
This means, there is no way the to read back pixels from the framebuffer on the adapter, only a "write to memory" feature. This means the Amiga has to have a copy of the current framebuffer in memory. One could save the memory for the delta buffer, if the MMU would be used to calculate accesses (like the Savage Shapeshifter driver).
Except for the decompression, I expect the device to be rather simple hardwarewise -- maybe the registers of the DVI encoder chip are directly accessible over control transfers. If that's the case, luckily the docs of the chip are available on the net.
The cruel & crucial point is still that I have to read that brainf*cking x86 code. Anyway. I'm at a stage now that I have identified and understood the display memory (16MB) accessing functions and can display a nice gradient. I also have found the registers that are used for the frame buffer start addresses, so I can actually switch between two memory locations now.
I have yet to find out the calculation for the video registers (I'm using a pre-recorded setup right now) and the delta-compression scheme, among other things of course.
new Linux GPL'ed drivers are available:
http://freedesktop.org/wiki/Software/libdlo
The lib is not that helpful yet, though DisplayLink have announced that they will extend it to also support "a" compression, whatever that means. There is more information about internal workings on our butterbrot site:
http://floe.butterbrot.org/displaylink/doku.php
If I'm going to pick up on it, it's going to be after the AROS Port of Poseidon. The Linux and X window guys are currently poking around the lib (but they are not really happy), so I'd wait some time to see what they find out...
PS: There's also a mailing list for the DisplayLink stuff, if you want to join it, contact FloE under the address echtler at fs dot tum dot de.
What's the current status on the USB commanded display adapter for Amiga project?
I found the project intriguing !
