A matter of Bits and Cartridges.

[dentnz]

SDRAM memory masking - This is now fixed. Writes to REU are out of the way of the 64k ram/rom the CPU can see. Reading back into the standard c64 area seems to work.
Counts - Seem to be fixed, albeit the length count returns to 01 still. Perhaps that's intended behavior, as it's what the Ultimate1541 REU does... Though I have read that compatibility isn't perfect with that implementation.
FF00 Trigger - This is done. Any kind of writing to this memory location will trigger an execute on the DMA transfer.

Speed - I've removed some of the delays that I addd to the code and it still seems to be functional if I allow 3 sdram operations to pass (I wait for the third sdram_ces pulse). I don't however think I am doing things right here still, see below...
Buggy transfers - Though it seems to be a lot more solid, I am STILL getting the odd crash during/after a transfer.

So I attempted to run some example REU software. The first is a basic/machine code combo that is supposed to test the REU. I've yet to disassemble the binary file to see what it is doing exactly, but suffice to say it's not working. The REU is detected and the test begins, but soon the border appears to shrink and the screen locks up. Any of the other demos appear to lock up almost immediately - albeit I have seen transfers begin, but then seem to stop.

My next line to explore is the speed/timing and trying to eliminate any further buggy transfers.

[LamerDeluxe]

Sounds like you are getting really close to a version that works with existing software, that will be a really nice pay-off. Respect for all the work you've been putting into this.

[dentnz]

Oh yeah, I just remembered I hadn't posted an update. Here's a video I made last Friday:

https://www.youtube.com/watch?v=xuXIE-egRrY

There's some kind of off by one error, either it's not getting ALL the bytes, or it's missing the first byte somewhere along the line. I will keep investigating.