The files USRTB.MAC, YRDRV.MAC, and YTDRV.MAC are parts of 2 drivers
for a DL11 on RSX11S for communications. YRDRV is for receiving data
to the RSX11S system and YTDRV sends data out. Both look like terminals
to RSX11S but send or recieve 8 bit data. They are much faster than
the TT driver. The YRDRV code has a check so that receive terminates
either on byte count expiring or on receipt of an octal 377 character.
You can change the terminator as you like but it's hardcoded in. Modify
source if you dislike it.
No type-ahead buffer is supported here and boundary conditions
are not thoroughly tested, but the I/O is known to work right for read
or write virtual/logical block. You use drivers like this where the TT
driver isn't fast enough. Unlike the DEC XL driver, these act like terminals
with no special protocols required, so you can switch to using them from
code you tried to use the TT driver with. Output to YRDRV or input to
YTDRV should just be ignored and complete instantly.
The RSX11S TT driver can handle about 750 chars/sec at 9600
baud when going out one line and into another; about 950 at 19200 baud
and about 1150 at 38400 baud. This driver handles 960 chars/sec at
9600 baud, about 1912/sec at 19200 baud, and about 2300 at 38400
baud. Both cases are out one port, in another, so the number of interrupts
is doubled. These timings are on an 11/23 with relatively slow memory.

Window is a VMS V4.0 or later multiwindow system (up to 10 glass
TTY windows.) A more sophisticated one is in the works...