DL11 — serial line, and the KW11 line clock

The DL11 is DEC’s single-line asynchronous serial interface, the card that carries a PDP-11’s console terminal. QUniLator models the DL11-W (M7856): four registers at 777560 — receiver status and buffer, transmitter status and buffer — with the receiver interrupting at vector 60 and the transmitter at 64, both at BR4. Its line runs on one of the BeagleBone’s UARTs, or over the network. It is listed as DL11, of type slu_c.

A second line, DL11b, sits at 776500 with vectors 300 and 304, on the cape’s UART1 (ttyS1) at 38400 baud, with errorbits off and break on.

The DL11-W carries a line clock as well, which QUniLator lists as a device of its own: KW11, below.

What the machine sees

Registers	RCSR 777560, RBUF 777562, XCSR 777564, XBUF 777566
Interrupts	Receive at vector 60, transmit at 64, both BR4
Receiver	One character. A character from the serial port or the network that arrives before the program has read the one before it overwrites it, and with errorbits on sets the overrun bit. A character from the web console waits until the program has read the one before it
Transmitter	One character at a time, paced at baudrate
Maintenance	XCSR bit 2 loops the transmitter back into the receiver
BREAK	A BREAK received on the line reads as a null character with the framing error bit set. Sending one takes break on and a serial port

Using it

Whether to enable it depends on the processor in the box. A processor with a console line of its own — an 11/53, an 11/73 — already answers at 777560, so DL11 stays disabled, and its console reaches the board through the external console bridge on ttyS2 (see the machine settings). A processor with no console line, such as the KDJ11-A, and the PDP-11 processors QUniLator emulates on a UniBone use DL11 as their console:

1. Set External console to Off on the Machine screen. The bridge and the DL11 cannot both hold ttyS2: with the bridge holding it, enabling DL11 answers with enabled still false, and the log says Another process has locked the comport.
2. Enable DL11 with serialport at ttyS2 and no tcp_role. A DL11 with neither a serial port it can open nor a network role refuses the enable.

The web console reaches DL11 on the WebSocket /ws/console/0, and DL11b on /ws/console/1, alongside whatever is on the line itself.

One character at a time

The DL11 holds a single received character. On the serial port and on a network line, typing into it faster than the program reads — pasting, or a script sending a whole line at once — loses characters: ra(0,0,0)unix arrives as r,)x. A program driving the console sends one character and waits for its echo before the next, or waits a moment per character where nothing echoes.

What arrives through the web console waits for the program instead: each character goes into the receiver when the program has read the one before it, so a paste reaches a slow guest whole.

A DL11 line can run over the network as well: set it to a TCP port, a host:port to dial, or ws for a browser terminal, as described under tcp_role. Both lines default to port 4200, which they then share: a caller reaches whichever of them is free.

What has been verified

• The DL11 has been the system console of a UniBone’s emulated PDP-11/34 and of a KDJ11-A on a QBone, which has no console line of its own.

Parameters

Settings

What a configuration stores and an operator sets.

Parameter	Short	Value	Default	What it is
serialport	p	text	ttyS2	Linux serial port: “ttyS1” or “ttyS2”
baudrate	b	number	9600	Baudrate: 110, 300, … 38400
mode	m	text	8N1	Mode: 8N1, 7E1, …
errorbits	eb	0 or 1	1	Enable error bits (M7856 SW4-7)
break	brk	0 or 1	1	Enable BREAK transmission (M7856 SW4-1)
tcp_role	tr	text	empty	TCP role: "" = use serial port, “listen”, “connect” or “websocket”
tcp_host	th	text	empty	TCP connect-out target host (tcp_role=connect)
tcp_port	tp	number	4200	TCP listen/connect port
tcp_idle_timeout	ti	number, s	0	drop a silent TCP client after N seconds, 0 = never

It also carries the parameters under parameters every card on the bus has.

In detail

serialport, baudrate, mode

The board’s UART the line drives while tcp_role is empty: ttyS2 is the cape’s UART2, ttyS1 its UART1. baudrate is a standard rate from 50 to 57600, and mode is data bits, parity and stop bits in three characters: 8N1, 7E1, 8O2. A port, rate or mode the board cannot open refuses the enable. All three are read when the device is enabled and are locked while it is. On a line carried over the network serialport is unused, mode sets the data bits the line carries, and baudrate sets the character time both directions are paced at.

errorbits

Switch SW4-7 on the M7856. On, a received character that had a framing or parity error, or arrived before the program read the one before it, sets the matching error bit in RBUF together with bit 15. Off, RBUF carries the character alone.

break

Switch SW4-1 on the M7856. On, the BREAK bit in XCSR holds the serial port’s transmit line spacing for as long as the program keeps it set, which is how a program sends BREAK; a TU58 needs it. A line carried over the network has no break condition to send.

tcp_role, tcp_host

Carries the line over the network. listen accepts one client on tcp_port, speaking Telnet with RFC 2217; connect dials tcp_host:tcp_port and dials again when the connection drops; websocket carries the line on the board’s WebSocket /ws/serial/<device>/0, for a browser terminal. Empty, the line runs on serialport. The Configurations screen edits the three as one field: a bare port listens, host:port connects, ws is the browser terminal.

A line that is already on the network can be retuned while the device is enabled; the change takes effect at once and drops a connected client. Moving a line between the UART and the network takes disabling the device first.

tcp_port

The port listen accepts on, or connect dials. Lines that listen on the same port share it: a caller reaches whichever of them is free, and is refused while all are busy. A port another program holds refuses the enable.

tcp_idle_timeout

Drops a client that has sent nothing for this many seconds, so a forgotten session does not hold the line. 0 keeps a client for as long as it stays connected. Read when the line opens.

The KW11 line clock

The KW11 is the line-time clock: it interrupts at mains frequency, 50 or 60 times a second, which is the tick an operating system keeps time by. Its one register, LKS at 777546, has an interrupt enable (bit 6) and a monitor bit (bit 7) that each tick sets and the program clears. It interrupts at vector 100, BR6. It is listed as KW11, of type ltc_c.

QBUS · QBone

A QBUS processor takes its line clock from the BEVNT line, which a power supply or an external clock drives. On a backplane that has one, the KW11 is not needed; enable it on a machine with no line clock.

Settings

What a configuration stores and an operator sets.

Parameter	Short	Value	Default	What it is
Line clock frequency	freq	number	50	50/60 Hz
LTC input enable	ltc	0 or 1	1	1 = enable update of LKS by LTC Input

It also carries the parameters under parameters every card on the bus has.

In detail

Line clock frequency

The mains frequency the clock ticks at, 50 or 60 Hz; another value is accepted with a warning, and 0 is refused. Each tick sets LKS bit 7 and, with LKS bit 6 set, interrupts. Ticks the board delivers late are made up by the ones after them, which come at up to twice the rate until the count has caught up with real time. A change takes effect at the next tick.

LTC input enable

The clock input. Off, the clock stops ticking: LKS bit 7 stays clear and no interrupt comes.