The DL-11 and friends only have single-character receive and transmit buffers, so an interrupt is generated for every character received or transmitted. Attempting to receive data at even moderately high rates will cause rx overruns. Fast transmission seems to be fine though.
There is no support in the driver for the paper-tape reader on an LT33 attached via a DLV-11KA or similar.
The overrun message is logged in the interrupt routine itself, which will probably just make the problem worse.
The CSR printed on startup is that of the receiver, while the interrupt vector is that of the transmitter.
In order to determine the card's interrupt vector, the driver sends a
NUL to each port. This may confuse things attached to them.
The driver has so far only been tested on a DLV-11J. It may or may not work on the other cards it claims to support.