VXI 11 and HiSLIP

Since 0.5.0 scpi-sim speaks the two VISA LAN protocols besides the raw socket. If your script opens one of these, it runs against the simulator unchanged — only the address changes:

Your script opens	Protocol	Start scpi-sim with
TCPIP::192.168.1.20::5025::SOCKET	raw socket	nothing extra
TCPIP::192.168.1.20::INSTR or ::inst0::INSTR	VXI-11	--vxi11
TCPIP::192.168.1.20::hislip0::INSTR	HiSLIP	--hislip

$ scpi-sim serve --hislip --vxi11 --no-portmapper --profile keysight-34461a
scpi-sim: keysight-34461a (34461A) listening on 127.0.0.1:5025 (Ctrl+C to stop)
scpi-sim: HiSLIP on 127.0.0.1:4880
scpi-sim: VXI-11 on 127.0.0.1:40651, no port mapper
scpi-sim:   keysight-34461a (34461A): TCPIP0::127.0.0.1::hislip0::INSTR
scpi-sim:   keysight-34461a (34461A): TCPIP0::127.0.0.1,40651::inst0::INSTR

The last lines are the resource strings to use. The options go before the instrument (serve --hislip psu) and work with --profile and --bench too.

Which one should I use?

• HiSLIP is the easy one: one fixed port (4880), no privileges needed, and it is what newer instruments recommend. If your script can use hislip0, use that.
• VXI-11 is what older scripts and most TCPIP::host::INSTR strings mean. It needs a port mapper — see the next section.
• The raw socket stays the simplest for new code and for tools that are not VISA (nc, C# TcpClient, LabVIEW TCP functions).

VXI-11 and port 111

A VXI-11 client first asks the port mapper on port 111 where the instrument listens, then connects there. scpi-sim brings its own port mapper, but port 111 is a privileged port, and on many Linux machines rpcbind already uses it. Pick what fits:

Situation	Do this	Resource string
Docker available	run the image; it serves the port mapper on 111	TCPIP0::localhost::psu::INSTR
PyVISA-py, no Docker	--vxi11 --no-portmapper	TCPIP0::127.0.0.1,PORT::inst0::INSTR (PORT from the output)
fixed port, e.g. for a firewall	--vxi11 --vxi11-port 5098 --no-portmapper	TCPIP0::127.0.0.1,5098::inst0::INSTR
NI-VISA / Keysight VISA, Linux	port mapper must be on 111: Docker, or root, or stop rpcbind	TCPIP0::127.0.0.1::inst0::INSTR

The host,PORT form skips the port mapper. PyVISA-py understands it; NI-VISA and Keysight VISA do not, they always ask port 111.

Docker with everything published:

docker run --rm -p 5025-5027:5025-5027 -p 111:111 -p 111:111/udp -p 5098:5098 -p 4880:4880 \
  ghcr.io/steitec/scpi-sim

Map 5098 to the same port outside: the port mapper reports the port inside the container.

Device names on a bench

One simulator serves several instruments on one VXI-11 port and one HiSLIP port, so the device name in the resource string picks the instrument:

	by position in the bench file	by name
VXI-11	inst0, inst1, …	psu, dmm, …
HiSLIP	hislip0, hislip1, …	hislip_psu, hislip_dmm, …

PyVISA-py treats a device name as HiSLIP only if it starts with hislip, hence hislip_psu rather than psu. From Python, bench.resource("psu", "hislip") and bench.resource("psu", "vxi11") build the right string, including the port when it is not the standard one.

Differences from the raw socket

VXI-11 and HiSLIP follow the IEEE 488.2 message exchange rules; the raw socket just streams lines. You notice it in four places:

1. An answer waits until you read it. write("*IDN?") then read() works. read() after a command without a query (write("VOLT 5")) runs into the client's timeout — as on a real instrument.
2. Query interrupted. Writing a new message before reading the previous answer discards that answer and puts -410,"Query INTERRUPTED" in the error queue. This finds a classic bug: a write("MEAS?") whose answer is never read.
3. Status byte. read_stb() works without sending *STB?; bit 4 (MAV, 16) is set while an answer waits, bit 2 (4) while the error queue is not empty.
4. Device clear. clear() drops pending input and answers — also a delayed one — but keeps the error queue and the settings.

Locks (lock_excl() / unlock() over VXI-11; AsyncLock in HiSLIP) are exclusive and shared across both protocols: a VXI-11 link and a HiSLIP session cannot hold the same instrument at the same time. PyVISA-py does not implement HiSLIP locks itself, so over HiSLIP you can only use them from other clients. A lock is released when its link is destroyed or when the client's connection closes; since 0.7.2 that covers every link the connection opened, not only the first.

Faults work on every transport: no_response, delay (a device clear cancels a delayed answer), disconnect (closes the VXI-11 link or the whole HiSLIP session).

Not supported

Service requests (SRQ, the VXI-11 interrupt channel), device_docmd, HiSLIP overlapped mode, HiSLIP 2.0 (TLS, authentication), shared locks (granted as exclusive), GPIB-over-LAN names such as gpib0,5, mDNS discovery.

Tested with PyVISA-py on Linux, Windows and macOS. Not yet verified with NI-VISA or Keysight VISA — if you try it, please report how it went.