darkon: I have checked a number of options but I am unable to make the 'freezer' function appear using the RESTORE key.
Also I found a DNP as drive D: is actually broken at this time :-(, but a DNP on sd2iec on drive C: would work (!)
Reaching U2 freezer:
I've implemented the freezer function using a keyboard 'special function' (these include trackdisplay, pause key, 40col Left/Right, reset MfM, new: F8=dou2freeze and F9=ulitprog)
The dou2freeze is then (only) available if your keymap has (some) key(-combo) assigned to 'F8'.
You can edit this in keyfig (this still works 'of course'). The default is mapped to CTRL+HELP
As you may (or may not ;-) know, the Z80 is unable to 'see' the RESTORE key. This BIOS will sometimes check the 40/80 key (needs to 8502 for that) so it would be possible to trap a RESTORE key but I didn't do anything specifically for that. I did (try to) make sure the NMI vector is causing a direct return from interrupt though!
Are you using any CPM tools other than the BIOS to reach UltimateII freezer?
The code I use to call the U2 freezer brings me back to the C128 CPM environment in a BIOS controlled way so I would need more info on your setup to mimic what is happening in your case.
Note on Keyboard:
Note that this BIOS actually has 2 keyboard layouts present. If you have an international version of the C128 (and the German one is most notable) then you can dynamically switch between US and German layouts using the 'CAPS LOCK' key (labelled ASCII/DIN on a German system). This will (also) update the VDC characters to match the expectation of German printers (back in the 80s that is)
Since I didn't like being unaware of the CAPS function hidden under the C= key, I added a short info reading 'CAPS' or 'NORM' to signal the state of the keyboard.
Note on DNP:
Since you use the ultimate II, I would have expected you to use the DNP via that (because faster).
Suppose your DNP is on usbx/cpm/test.dnp (you can create dnp using the F5 menu / Create / DNP: name / tracks 255)
Select the DNP and enter it. F5 / Software IEC / Set dir. here
Your U2 on ID11 means the DNP file will appear on drive D. At boot, the BIOS detects the 'UCI' drive on A or B or D and will then swap the buffer-allocation with drive E.
That allows a large disk mounted on D:
Since C: also has a large buffer allocated, you should be able to use a DNP file via the sd2iec there as well (albeit via the slow IEC protocol, I don't know if Jiffy Dos speeds up the block read/write U1/U2 as well)
Even if we assume you can use Jiffy, then the UCI access will still be faster (but not that much)
(I have no sd2IEC so I have trouble verifying my design with that.)
Error: Now, if the UCI drive (D:), I notice the BIOS isn't correctly mapping the buffers :-( So I'll be following up on that.
If the UCI is on E: this would still not get you the 16M drive since CPM will think this is a c64 disk (single side 1541 with c64 layout). That's not what we want.
I've developed a tool (cmdinst.com) which sets up the boot block of the drive (developed for CMD HD...) so that a DNP will be recognized as a 16Mb drive.
I'll follow up on the buffer-swap design and provide an update when that works, so that your setup will be OK.
In the meantime, if you don't mind, please share what your CPM system startup does (or even that link to your 16Mb Reu)