Layer: L7 Application · Build flags: PC_ENABLE_GPIB

What this example teaches

A huge installed base of bench instruments speaks only IEEE-488 (GPIB) and will never talk SCPI-over-TCP directly. A Prologix GPIB-Ethernet adapter bridges them onto the LAN: you open a raw TCP socket (port 1234) and speak the Prologix ++ command language. services/gpib is a pure codec for that command set; the sketch owns the socket.

A line starting with ++ is a controller command; anything else is data forwarded over GPIB to the addressed instrument. Configure the adapter, then send SCPI as data:

pc_gpib_command(cmd, sizeof(cmd), "mode 1");            // controller-in-charge
pc_gpib_addr(cmd, sizeof(cmd), 9, -1);                  // ++addr 9  (instrument address)
pc_gpib_eos(cmd, sizeof(cmd), GpibEos::LF);             // ++eos 2   (append LF over GPIB)
pc_gpib_command(cmd, sizeof(cmd), "eoi 1");             // assert EOI on the last byte
pc_gpib_build_data(data, sizeof(data), (const uint8_t *)"*IDN?", 5);  // send SCPI as data
pc_gpib_read(cmd, sizeof(cmd), GpibRead::UNTIL_EOI, 0); // ++read eoi -> read the reply

The data escaping is the subtle part: each CR / LF / ESC / + byte in the payload is preceded by an ESC (27) so it is not eaten as a line terminator or mistaken for a command - verified byte-exact against the Prologix manual's binary example. Response parsers cover the serial-poll status byte (pc_gpib_parse_decimal after ++spoll), the address, and the ++ver string.

Prerequisites (a Prologix adapter)

Point ADAPTER_IP at a Prologix GPIB-Ethernet controller (or an AR488-Ethernet build) with a GPIB instrument at INSTRUMENT_ADDR. No adapter handy? A Prologix-emulating socket server on a host works for a dry run.

Build and run

pio ci --board=esp32dev --project-option="framework=arduino" \
  --project-option="build_flags=-DPC_ENABLE_GPIB=1" \
  --lib="." examples/L7-Application/Gpib/Gpib.ino

Flash and watch Serial @ 115200:

IP: 192.168.1.42
[gpib] *IDN? -> HEWLETT-PACKARD,34401A,0,11-5-2
[gpib] adapter version 1.6.6.0
[gpib] done

Annotated source

The complete sketch is Gpib.ino. The codec itself is in src/services/instrumentation/gpib/gpib.h; the command set, the ++eos mapping, the data-escaping rule, and the TCP port are verified against the Prologix GPIB-Ethernet and GPIB-USB controller manuals (cross-checked with AR488).