For a current list of known issues refer to the GitHub Issues web page.
Technically, they should be presented separately to the guest O/S: CE upon completion the actual rewind-unload CCW and then DE once the tape actually finishes unloading, but doing so is somewhat problematic especially for SCSI tapes. (Might be possible to do for AWS/HET tapes but I haven't looked into it yet).
Final DE on Rewind Unload must be accompanied by UC (Unit Check) (all device types) and possibly CUE (Control Unit End) for 3420 (3803 Control Unit Type, to indicate an end of Control Unit Busy condition). It is possible the CUE should only occur if a BUSY was presented at some point, but I am not 100% sure about that (and that's not supported either, as we don't support shared Control Units). However, VM/370 for example insists that CUE be presented.
On the same line, VM/370 DDR is failing on Rewind unload. This could be part of the above problem.
The current AWS handler is not capable of processing multi-segment blocks. However, this can be bypassed by forcing the use of the HET handler which is backward compatible.
Because of the current I/O design, where we prefetch all write data prior to issuing the I/O, program check is presented unconditionally (except for immediate commands which are declared as such by the device handlers) even though, technically, it should only be presented if the Control Unit (device handler) attempts to consume data from the offending address.
The I/O subsystem reset function does not actually send a reset signal to the device handlers as described in section 17.2.2.2 of the Principles of Operation. If an I/O is in progress when the reset occurs, it will not be terminated.
Subsequently, if status is stacked after the I/O reset, the device may be left in an unusable state, with status pending and E bit off, effectivelly preventing an MSCH to be issued with the E bit on, requiring a Power On Reset (Hercules poweroff and restart of the emulator). Only ESA/390 and ESAME are affected.
I/O architecture requires non-ready units to return UC (Unit Check) only. This is done at the device handler lever and has not been implemented in all device handlers.
Pressing enter while in single step mode used to be the equivalent of pressing the start button
(which was quite handy for debugging). It now displays the last commands typed. Instead, the
start command must be typed each time to execute the next instruction when in single step mode.