Layer: L7 Application · Build flags: PC_ENABLE_SCPI

What this example teaches

SCPI (Standard Commands for Programmable Instruments) is the text command language nearly every modern bench instrument speaks - DMMs, oscilloscopes, power supplies, function/arbitrary generators, SMUs, spectrum/network analyzers, electronic loads - over a raw TCP socket on port 5025 (PC_SCPI_PORT). services/scpi is a pure, transport-agnostic codec: it builds command lines and parses replies; the sketch owns the socket (a plain WiFiClient) and runs a small session against a real instrument.

pc_scpi_build joins a :-hierarchy header with comma-separated parameters and the newline terminator, and pc_scpi_common renders the 13 mandatory IEEE 488.2 common commands:

size_t n = pc_scpi_build(cmd, sizeof(cmd),
                          pc_scpi_common(ScpiCommon::SCPI_IDN_Q), nullptr, 0); // "*IDN?\n"
n = pc_scpi_build(cmd, sizeof(cmd), "MEASure:VOLTage:DC?", nullptr, 0);        // "MEASure:VOLTage:DC?\n"
const char *args[] = {"1.5"};
n = pc_scpi_build(cmd, sizeof(cmd), "SOURce:VOLTage", args, 1);                // "SOURce:VOLTage 1.5\n"

Replies are parsed without the standard library: pc_scpi_parse_number (NR1/NR2/NR3), pc_scpi_parse_bool (1/0/ON/OFF), pc_scpi_parse_string (quote-stripping), and pc_scpi_parse_block (the arbitrary block #<n><len><data> used for waveform captures):

double volts = 0.0;
if (pc_scpi_parse_number(resp, strlen(resp), &volts))
    Serial.printf("DC voltage = %.6f V\n", volts);

The codec is symmetric - it also carries the instrument side: the IEEE 488.2 status model (ScpiStatus - the Status Byte, Standard Event Status Register + enable masks, and the FIFO error/event queue via pc_scpi_push_error / pc_scpi_pop_error / pc_scpi_stb) and pc_scpi_match, a SCPI short/long-form + numeric-suffix header matcher for dispatching an incoming command against a pattern like "SYSTem:ERRor?". That side turns the device into a SCPI instrument itself; this sketch demonstrates the controller half.

Prerequisites (an instrument or a simulator)

Point INSTRUMENT_IP at anything that answers SCPI on TCP 5025. To dry-run without hardware, fake one on a host with a canned responder:

# a trivial SCPI stub: answers *IDN? and a voltage query, then closes

while true; do printf 'PC,SIM,0,1.0\n1.234567\n0,"No error"\n' | nc -l -p 5025 -q1; done

or use a Python pyvisa sim / any vendor SCPI simulator.

Build and run

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

Flash and watch Serial @ 115200:

IP: 192.168.1.42
[scpi] *IDN? -> KEYSIGHT TECHNOLOGIES,34470A,MY12345678,A.02.16
[scpi] DC voltage = 1.234567 V
[scpi] SYST:ERR? -> 0,"No error"
[scpi] done

Annotated source

The complete sketch is Scpi.ino. The codec itself is in src/services/instrumentation/scpi/scpi.h; the register bits, error-number classes, and exact standard error strings are verified against the SCPI-1999 standard and IEEE 488.2-1992.