std_rs/records/

epid.rs

use std::any::Any;
use std::time::Instant;

use epics_base_rs::error::{CaError, CaResult};
use epics_base_rs::server::recgbl::{self, alarm_status};
use epics_base_rs::server::record::{
    AlarmSeverity, CommonFields, FieldDesc, LinkType, ProcessAction, ProcessContext,
    ProcessOutcome, Record, link_field_type,
};
use epics_base_rs::types::{DbFieldType, EpicsValue};

/// Feedback mode for the epid record.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[repr(i16)]
pub enum FeedbackMode {
    #[default]
    Pid = 0,
    MaxMin = 1,
}

impl From<i16> for FeedbackMode {
    fn from(v: i16) -> Self {
        match v {
            1 => FeedbackMode::MaxMin,
            _ => FeedbackMode::Pid,
        }
    }
}

/// Feedback on/off state.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[repr(i16)]
pub enum FeedbackState {
    #[default]
    Off = 0,
    On = 1,
}

impl From<i16> for FeedbackState {
    fn from(v: i16) -> Self {
        match v {
            1 => FeedbackState::On,
            _ => FeedbackState::Off,
        }
    }
}

/// Extended PID feedback control record.
///
/// Ported from EPICS std module `epidRecord.c`.
/// Supports PID and Max/Min feedback modes with anti-windup,
/// bumpless turn-on, output deadband, and hysteresis-based alarms.
pub struct EpidRecord {
    // --- PID control ---
    /// Setpoint (VAL)
    pub val: f64,
    /// Setpoint mode: 0=supervisory, 1=closed_loop (SMSL)
    pub smsl: i16,
    /// Setpoint input link (STPL) — resolved by framework
    pub stpl: String,
    /// Controlled value input link (INP) — resolved by framework
    pub inp: String,
    /// Output link (OUTL) — resolved by framework
    pub outl: String,
    /// Readback trigger link (TRIG)
    pub trig: String,
    /// Trigger value (TVAL)
    pub tval: f64,
    /// Controlled value (CVAL), read-only
    pub cval: f64,
    /// Previous controlled value (CVLP), read-only
    pub cvlp: f64,
    /// Output value (OVAL), read-only
    pub oval: f64,
    /// Previous output value (OVLP), read-only
    pub ovlp: f64,
    /// Proportional gain (KP)
    pub kp: f64,
    /// Integral gain — repeats per second (KI)
    pub ki: f64,
    /// Derivative gain (KD)
    pub kd: f64,
    /// Proportional component (P), read-only
    pub p: f64,
    /// Previous P (PP), read-only
    pub pp: f64,
    /// Integral component (I), writable for bumpless init
    pub i: f64,
    /// Previous I (IP)
    pub ip: f64,
    /// Derivative component (D), read-only
    pub d: f64,
    /// Previous D (DP), read-only
    pub dp: f64,
    /// Error = setpoint - controlled value (ERR), read-only
    pub err: f64,
    /// Previous error (ERRP), read-only
    pub errp: f64,
    /// Delta time in seconds (DT), writable for fast mode
    pub dt: f64,
    /// Previous delta time (DTP)
    pub dtp: f64,
    /// Minimum delta time between calculations (MDT)
    pub mdt: f64,
    /// Feedback mode: PID or MaxMin (FMOD)
    pub fmod: i16,
    /// Feedback on/off (FBON)
    pub fbon: i16,
    /// Previous feedback on/off (FBOP)
    pub fbop: i16,
    /// Output deadband (ODEL)
    pub odel: f64,

    // --- Display ---
    /// Display precision (PREC)
    pub prec: i16,
    /// Engineering units (EGU)
    pub egu: String,
    /// High operating range (HOPR)
    pub hopr: f64,
    /// Low operating range (LOPR)
    pub lopr: f64,
    /// High drive limit (DRVH)
    pub drvh: f64,
    /// Low drive limit (DRVL)
    pub drvl: f64,

    // --- Alarm ---
    /// Hihi deviation limit (HIHI)
    pub hihi: f64,
    /// Lolo deviation limit (LOLO)
    pub lolo: f64,
    /// High deviation limit (HIGH)
    pub high: f64,
    /// Low deviation limit (LOW)
    pub low: f64,
    /// Hihi severity (HHSV)
    pub hhsv: i16,
    /// Lolo severity (LLSV)
    pub llsv: i16,
    /// High severity (HSV)
    pub hsv: i16,
    /// Low severity (LSV)
    pub lsv: i16,
    /// Alarm deadband / hysteresis (HYST)
    pub hyst: f64,
    /// Last value alarmed (LALM), read-only
    pub lalm: f64,

    // --- Monitor deadband ---
    /// Archive deadband (ADEL)
    pub adel: f64,
    /// Monitor deadband (MDEL)
    pub mdel: f64,
    /// Last value archived (ALST), read-only
    pub alst: f64,
    /// Last value monitored (MLST), read-only
    pub mlst: f64,

    // --- Internal time tracking ---
    /// Current time (CT) — used for delta-T computation
    pub(crate) ct: Instant,
    /// Previous time (CTP) — tracked for monitor change detection
    #[allow(dead_code)]
    pub(crate) ctp: Instant,

    // --- Internal flags ---
    /// Set by the framework (via set_device_did_compute) to indicate
    /// device support's read() already performed the PID computation.
    /// process() checks this to avoid running the built-in PID a second time.
    device_did_compute: bool,
    /// Set by `do_pid` when the `INP` link is a CONSTANT link (a literal
    /// value, not a PV reference). C `devEpidSoft.c:110-112`
    /// (`if (pepid->inp.type == CONSTANT) recGblSetSevr(...,SOFT_ALARM,
    /// INVALID_ALARM)`): with a constant INP there is "nothing to
    /// control", so the PID compute is skipped and SOFT/INVALID is
    /// raised. The framework `check_alarms` hook reads this flag and
    /// applies the severity via `recGblSetSevr`.
    pub inp_constant: bool,
    /// Framework-owned `dbCommon.udf`, pushed by the framework via
    /// [`Record::set_process_context`] immediately before `process()`.
    /// C `epidRecord.c:195` reads `pepid->udf` at the top of
    /// `process()` and skips `do_pid` entirely while it is set. The
    /// matching `UDF_ALARM` (C `epidRecord.c:199`,
    /// `recGblSetSevr(pepid,UDF_ALARM,pepid->udfs)`) is raised by the
    /// framework's centralised `rec_gbl_check_udf` after `process()`.
    udf: bool,
    /// Set by `process()` for a cycle on which the UDF gate skipped
    /// `do_pid`. C `epidRecord.c:201` `return(0)` is reached before
    /// `recGblFwdLink` and before `do_pid` writes the output, so on
    /// such a cycle the framework must NOT write the OUTL link
    /// (`multi_output_links`) or fire the forward link.
    compute_skipped: bool,
    /// True iff the framework's input-link fetch for `STPL` actually
    /// produced a value this cycle — the framework analogue of C
    /// `RTN_SUCCESS(dbGetLink(&prec->stpl, ...))`. Pushed by the
    /// framework via [`Record::set_resolved_input_links`] after the
    /// `multi_input_links` fetch (STPL is only in that list when
    /// `SMSL == closed_loop`). C `epidRecord.c:191-193` clears `udf`
    /// only on this success — a STPL that is empty, or a DB/CA link
    /// whose fetch failed, leaves `udf` set.
    stpl_resolved: bool,
    /// Framework-owned `dbCommon.dtyp`, pushed by the framework via
    /// [`Record::set_process_context`] before the input-link fetch.
    /// C device support for the epid record lives in two distinct
    /// DSETs — `devEpidSoft` (`devEpidSoft.c`, no TRIG handling) and
    /// `devEpidSoftCallback` (`devEpidSoftCallback.c`, which drives the
    /// TRIG readback link). [`Record::pre_input_link_actions`] checks
    /// this to emit the TRIG write only when the callback DSET (DTYP
    /// `"Epid Async Soft"`) is selected.
    dtyp: String,
    /// Epid-owned `dbCommon.udf` projection, returned by
    /// [`Record::value_is_undefined`]. C `epidRecord.c` has
    /// `special = NULL` (line 105) — there is no operator UDF clear,
    /// and `udf` is cleared ONLY by the two C conditions:
    ///
    /// - `epidRecord.c:160-164` init: a CONSTANT `STPL` link holding
    ///   a valid constant clears `udf` (mirrored by
    ///   [`Record::post_init_finalize_undef`] / a CONSTANT `STPL`
    ///   making `value_is_undefined()` return `false`).
    /// - `epidRecord.c:191-193` process: closed-loop (`SMSL=1`) with
    ///   a successful `dbGetLink(stpl)` clears `udf`.
    ///
    /// `process()` recomputes this each cycle; the framework's
    /// post-process `common.udf = value_is_undefined()` then keeps a
    /// supervisory / empty-STPL epid permanently undefined, exactly as
    /// C leaves `udf == TRUE` forever for such a record.
    value_undefined: bool,
    /// Set by [`crate::device_support::epid_soft_callback::
    /// EpidSoftCallbackDeviceSupport::read`] on the first (trigger) pass
    /// of a CA-type TRIG link, cleared by `process()`.
    ///
    /// C `devEpidSoftCallback.c:143-145`: a CA TRIG link fires the
    /// readback trigger asynchronously (`dbCaPutLinkCallback`), sets
    /// `pepid->pact = TRUE` and `return(0)`. C `epidRecord.c:207`
    /// `if (!pact && pepid->pact) return(0)` then returns BEFORE
    /// `recGblGetTimeStamp` / `checkAlarms` / `monitor` /
    /// `recGblFwdLink` — so the trigger pass runs NONE of the
    /// process tail; the tail runs exactly once, on the callback
    /// (reprocess) pass.
    ///
    /// The Rust framework runs device support `read()` before
    /// `process()`; `read()` cannot itself short-circuit the cycle.
    /// This flag is `read()`'s signal to `process()` that the cycle is
    /// a CA-trigger pass — `process()` consumes it and returns
    /// `ProcessOutcome::async_pending()`, which makes the framework
    /// skip the alarm/timestamp/snapshot/OUT/FLNK tail for this cycle
    /// (the `read()`-returned `WriteDbLink{TRIG}` + `ReprocessAfter`
    /// actions are still executed). The reprocess pass runs `do_pid`
    /// and the tail exactly once.
    ca_trig_pending: bool,
}

impl Default for EpidRecord {
    fn default() -> Self {
        let now = Instant::now();
        Self {
            val: 0.0,
            smsl: 0,
            stpl: String::new(),
            inp: String::new(),
            outl: String::new(),
            trig: String::new(),
            tval: 0.0,
            cval: 0.0,
            cvlp: 0.0,
            oval: 0.0,
            ovlp: 0.0,
            kp: 0.0,
            ki: 0.0,
            kd: 0.0,
            p: 0.0,
            pp: 0.0,
            i: 0.0,
            ip: 0.0,
            d: 0.0,
            dp: 0.0,
            err: 0.0,
            errp: 0.0,
            dt: 0.0,
            dtp: 0.0,
            mdt: 0.0,
            fmod: 0,
            fbon: 0,
            fbop: 0,
            odel: 0.0,
            prec: 0,
            egu: String::new(),
            hopr: 0.0,
            lopr: 0.0,
            drvh: 0.0,
            drvl: 0.0,
            hihi: 0.0,
            lolo: 0.0,
            high: 0.0,
            low: 0.0,
            hhsv: 0,
            llsv: 0,
            hsv: 0,
            lsv: 0,
            hyst: 0.0,
            lalm: 0.0,
            adel: 0.0,
            mdel: 0.0,
            alst: 0.0,
            mlst: 0.0,
            ct: now,
            ctp: now,
            device_did_compute: false,
            inp_constant: false,
            dtyp: String::new(),
            udf: true,
            compute_skipped: false,
            stpl_resolved: false,
            // C `epidRecord.c` init: `udf` starts TRUE and is cleared
            // only by the two clear-conditions — see `value_undefined`.
            value_undefined: true,
            ca_trig_pending: false,
        }
    }
}

impl EpidRecord {
    /// Decide the alarm condition using hysteresis-based threshold
    /// comparison on VAL. Ported from epidRecord.c `checkAlarms()`,
    /// which mirrors `aiRecord.c::checkAlarms` — per-level hysteresis
    /// against VAL with `lalm` tracking the last-alarmed threshold.
    ///
    /// Returns `Some((stat, sevr, alev))` where `stat` is the canonical
    /// `epicsAlarmCondition` status code (`HIHI_ALARM`, `HIGH_ALARM`,
    /// `LOLO_ALARM`, `LOW_ALARM`), `sevr` the configured severity, and
    /// `alev` the threshold that fired (the candidate `lalm` value).
    /// Returns `None` when VAL is inside the (hysteresis-adjusted) limits.
    ///
    /// `lalm` (last-alarmed threshold) is committed by the caller, NOT
    /// here, for the alarm case. C `aiRecord.c:403-406` gates the `lalm`
    /// update on `recGblSetSevr` actually raising the severity:
    /// `if (recGblSetSevr(...)) prec->lalm = alev;`. A lower-severity
    /// alarm that loses to an already-higher pending severity must NOT
    /// advance `lalm`, or the hysteresis band would be silently re-based.
    /// The [`Record::check_alarms`] trait hook below performs that gate.
    ///
    /// The no-alarm case writes `lalm = val` here unconditionally,
    /// matching C `aiRecord.c:409` (`prec->lalm = val;` — not gated).
    pub fn check_alarms(&mut self) -> Option<(u16, AlarmSeverity, f64)> {
        let val = self.val;
        let hyst = self.hyst;
        let lalm = self.lalm;

        // HIHI alarm
        if self.hhsv != 0 && (val >= self.hihi || (lalm == self.hihi && val >= self.hihi - hyst)) {
            return Some((
                alarm_status::HIHI_ALARM,
                AlarmSeverity::from_u16(self.hhsv as u16),
                self.hihi,
            ));
        }

        // LOLO alarm
        if self.llsv != 0 && (val <= self.lolo || (lalm == self.lolo && val <= self.lolo + hyst)) {
            return Some((
                alarm_status::LOLO_ALARM,
                AlarmSeverity::from_u16(self.llsv as u16),
                self.lolo,
            ));
        }

        // HIGH alarm
        if self.hsv != 0 && (val >= self.high || (lalm == self.high && val >= self.high - hyst)) {
            return Some((
                alarm_status::HIGH_ALARM,
                AlarmSeverity::from_u16(self.hsv as u16),
                self.high,
            ));
        }

        // LOW alarm
        if self.lsv != 0 && (val <= self.low || (lalm == self.low && val <= self.low + hyst)) {
            return Some((
                alarm_status::LOW_ALARM,
                AlarmSeverity::from_u16(self.lsv as u16),
                self.low,
            ));
        }

        // No alarm — C `aiRecord.c:409` resets LALM to VAL unconditionally.
        self.lalm = val;
        None
    }

    /// Mark this cycle as a CA-TRIG trigger pass.
    ///
    /// Called by [`crate::device_support::epid_soft_callback::
    /// EpidSoftCallbackDeviceSupport::read`] on the first pass of a
    /// CA-type TRIG link, before `process()` runs. `process()` consumes
    /// the flag and returns `ProcessOutcome::async_pending()` so the
    /// trigger pass skips the process tail (checkAlarms / monitor /
    /// recGblFwdLink) — C `devEpidSoftCallback.c:143-145` +
    /// `epidRecord.c:205-210`. See [`EpidRecord::ca_trig_pending`].
    pub fn set_ca_trig_pending(&mut self) {
        self.ca_trig_pending = true;
    }

    /// Update monitor tracking fields. Returns list of fields that changed.
    /// Ported from epidRecord.c `monitor()`.
    pub fn update_monitors(&mut self) {
        // Update previous-value fields for change detection
        self.ovlp = self.oval;
        self.pp = self.p;
        self.ip = self.i;
        self.dp = self.d;
        self.dtp = self.dt;
        self.errp = self.err;
        self.cvlp = self.cval;

        // VAL deadband tracking
        if self.mdel == 0.0 || (self.mlst - self.val).abs() > self.mdel {
            self.mlst = self.val;
        }
        if self.adel == 0.0 || (self.alst - self.val).abs() > self.adel {
            self.alst = self.val;
        }
    }
}

static FIELDS: &[FieldDesc] = &[
    // PID control
    FieldDesc {
        name: "VAL",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "SMSL",
        dbf_type: DbFieldType::Short,
        read_only: false,
    },
    FieldDesc {
        name: "STPL",
        dbf_type: DbFieldType::String,
        read_only: false,
    },
    FieldDesc {
        name: "INP",
        dbf_type: DbFieldType::String,
        read_only: false,
    },
    FieldDesc {
        name: "OUTL",
        dbf_type: DbFieldType::String,
        read_only: false,
    },
    FieldDesc {
        name: "TRIG",
        dbf_type: DbFieldType::String,
        read_only: false,
    },
    FieldDesc {
        name: "TVAL",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "CVAL",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "CVLP",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "OVAL",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "OVLP",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "KP",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "KI",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "KD",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "P",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "PP",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "I",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "IP",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "D",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "DP",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "ERR",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "ERRP",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "DT",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "DTP",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "MDT",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "FMOD",
        dbf_type: DbFieldType::Short,
        read_only: false,
    },
    FieldDesc {
        name: "FBON",
        dbf_type: DbFieldType::Short,
        read_only: false,
    },
    FieldDesc {
        name: "FBOP",
        dbf_type: DbFieldType::Short,
        read_only: true,
    },
    FieldDesc {
        name: "ODEL",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    // Display
    FieldDesc {
        name: "PREC",
        dbf_type: DbFieldType::Short,
        read_only: false,
    },
    FieldDesc {
        name: "EGU",
        dbf_type: DbFieldType::String,
        read_only: false,
    },
    FieldDesc {
        name: "HOPR",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "LOPR",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "DRVH",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "DRVL",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    // Alarm
    FieldDesc {
        name: "HIHI",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "LOLO",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "HIGH",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "LOW",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "HHSV",
        dbf_type: DbFieldType::Short,
        read_only: false,
    },
    FieldDesc {
        name: "LLSV",
        dbf_type: DbFieldType::Short,
        read_only: false,
    },
    FieldDesc {
        name: "HSV",
        dbf_type: DbFieldType::Short,
        read_only: false,
    },
    FieldDesc {
        name: "LSV",
        dbf_type: DbFieldType::Short,
        read_only: false,
    },
    FieldDesc {
        name: "HYST",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "LALM",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    // Monitor deadband
    FieldDesc {
        name: "ADEL",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "MDEL",
        dbf_type: DbFieldType::Double,
        read_only: false,
    },
    FieldDesc {
        name: "ALST",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
    FieldDesc {
        name: "MLST",
        dbf_type: DbFieldType::Double,
        read_only: true,
    },
];

impl Record for EpidRecord {
    fn record_type(&self) -> &'static str {
        "epid"
    }

    /// Bumpless-transfer readback — C `devEpidSoft.c:153-158` (PID) and
    /// `devEpidSoft.c:178-184` / `devEpidSoftCallback.c:214-220`
    /// (MaxMin).
    ///
    /// On the feedback OFF->ON edge (`FBOP==0 && FBON!=0`) C seeds the
    /// turn-on state from the `OUTL` output link's *actual current
    /// value* via `dbGetLink(&pepid->outl, DBR_DOUBLE, ...)`, guarded by
    /// `outl.type != CONSTANT`. The seeded field differs by FMOD:
    ///
    ///   - PID (`fmod==0`), C `devEpidSoft.c:155`:
    ///     `dbGetLink(&pepid->outl, DBR_DOUBLE, &i, ...)` — the OUTL
    ///     readback lands in the integral term `I`.
    ///   - MaxMin (`fmod==1`), C `devEpidSoft.c:181` /
    ///     `devEpidSoftCallback.c:217`:
    ///     `dbGetLink(&pepid->outl, DBR_DOUBLE, &oval, ...)` — the OUTL
    ///     readback lands in the output value `OVAL`.
    ///
    /// The Rust framework's `ReadDbLink` pre-process action performs
    /// exactly that synchronous read of the DB link's target value into
    /// a record field, executed BEFORE `process()` / `do_pid` runs.
    ///
    /// `FBOP` still holds the *previous* cycle's `FBON` at this point
    /// (it is committed at the end of `do_pid`), so the edge is
    /// detectable here. The action is emitted only for a non-CONSTANT
    /// `OUTL` link, mirroring C's `outl.type != CONSTANT` guard — for a
    /// CONSTANT/empty `OUTL` the seeded field keeps its prior value.
    fn pre_process_actions(&mut self) -> Vec<ProcessAction> {
        let edge = self.fbon != 0 && self.fbop == 0;
        if edge {
            // PID seeds `I` from OUTL (devEpidSoft.c:153-158);
            // MaxMin seeds `OVAL` from OUTL (devEpidSoft.c:178-184).
            let target_field = if self.fmod == 0 { "I" } else { "OVAL" };
            match link_field_type(&self.outl) {
                LinkType::Db | LinkType::Ca => {
                    return vec![ProcessAction::ReadDbLink {
                        link_field: "OUTL",
                        target_field,
                    }];
                }
                _ => {}
            }
        }
        Vec::new()
    }

    fn process(&mut self) -> CaResult<ProcessOutcome> {
        // In the C code, process() always calls pdset->do_pid() — a custom
        // device support function unique to the epid record. In Rust, the
        // framework has a generic DeviceSupport trait with read()/write()
        // and no custom function pointers.
        //
        // For non-"Soft Channel" DTYPs (e.g. "Fast Epid"), the framework
        // calls DeviceSupport::read() BEFORE process(). That read() runs
        // the driver-specific PID and sets pid_done = true.
        //
        // For "Soft Channel" or no device support, the framework skips
        // read(), so pid_done stays false and process() runs the built-in
        // PID here.

        // C `epidRecord.c:189-203`: the UDF gate is taken only on the
        // non-callback pass (`if (!pact)`). `device_did_compute` is the
        // Rust equivalent of "device support already ran do_pid" — the
        // callback pass — so the gate applies only when it is false.
        //
        // C `epidRecord.c` clears `udf` ONLY at two sites (`special` is
        // NULL — there is no operator UDF clear):
        //   - `epidRecord.c:160-164` init: a CONSTANT `STPL` link with a
        //     valid constant. A constant link's value never changes, so
        //     it is "defined" on every cycle thereafter.
        //   - `epidRecord.c:191-193` process: closed-loop (`SMSL=1`)
        //     with `RTN_SUCCESS(dbGetLink(&prec->stpl, ...))` — an
        //     ACTUAL fetch success. `self.stpl_resolved` is the
        //     framework's report of exactly that (a STPL that is empty,
        //     or whose DB/CA fetch failed, leaves it false).
        // Otherwise `udf` stays TRUE forever and C `epidRecord.c:195`
        // `return(0)` skips `do_pid` every cycle — e.g. a supervisory
        // (`SMSL=0`) epid with an empty/non-constant STPL NEVER runs
        // `do_pid`.
        //
        // `self.udf` is the framework `dbCommon.udf` pushed before
        // `process()`; it is last cycle's value because the framework
        // recomputes `common.udf` (from `value_is_undefined()`) only
        // *after* `process()`. C reads `pepid->udf` at process-start
        // identically. `udf` is sticky-false: once C clears it, it is
        // never re-set — so the gate keys off `self.udf`, and a closed-
        // loop epid whose STPL later fails keeps running `do_pid`.
        //
        // `value_undefined` is recomputed here for the framework's
        // post-process `common.udf = value_is_undefined()`.
        self.compute_skipped = false;

        // CA-TRIG trigger pass — C `devEpidSoftCallback.c:143-145` +
        // `epidRecord.c:205-210`. `EpidSoftCallbackDeviceSupport::read`
        // ran first this cycle, saw a CA-type TRIG link, fired the
        // asynchronous readback trigger (returning `WriteDbLink{TRIG}` +
        // `ReprocessAfter` actions), and set `ca_trig_pending` — the
        // analogue of C `do_pid` setting `pepid->pact = TRUE` and
        // `return(0)`.
        //
        // C `epidRecord.c:207` `if (!pact && pepid->pact) return(0)`
        // then returns BEFORE `recGblGetTimeStamp` / `checkAlarms` /
        // `monitor` / `recGblFwdLink`: the trigger pass runs NONE of
        // the process tail. Return `async_pending` so the framework
        // skips the alarm/timestamp/snapshot/OUT/FLNK tail for this
        // cycle. The `read()`-returned actions were merged by the
        // framework and are still executed; the reprocess pass runs
        // `do_pid` and the tail exactly once.
        //
        // `device_did_compute` is cleared here because the trigger pass
        // performed NO compute — without this reset the reprocess pass
        // could observe a stale `true`.
        if self.ca_trig_pending {
            self.ca_trig_pending = false;
            self.device_did_compute = false;
            return Ok(ProcessOutcome::async_pending());
        }

        // C clear-conditions, evaluated at process-start:
        //  - CONSTANT STPL link  → init `recGblInitConstantLink` cleared
        //    udf permanently (`epidRecord.c:160-164`).
        //  - closed-loop STPL fetch succeeded this cycle
        //    (`epidRecord.c:191-193`).
        //
        // `stpl_resolved` is a per-cycle signal: consume it and reset
        // so a later `process_local`-path cycle (which performs no
        // link resolution and never calls `set_resolved_input_links`)
        // cannot read a stale "resolved" from an earlier links-path
        // cycle.
        let stpl_resolved = self.stpl_resolved;
        self.stpl_resolved = false;
        let stpl_clears_udf =
            link_field_type(&self.stpl) == LinkType::Constant || (self.smsl == 1 && stpl_resolved);
        // udf state this cycle: undefined unless already cleared
        // (`!self.udf`) or a clear-condition fires now.
        self.value_undefined = self.udf && !stpl_clears_udf;
        if !self.device_did_compute {
            if self.value_undefined {
                // C `epidRecord.c:195-202`: while `udf==TRUE`, skip
                // `do_pid` entirely and `return 0` — *before*
                // `recGblGetTimeStamp`, `checkAlarms`, `monitor` and
                // `recGblFwdLink`. The framework's centralised UDF
                // check (`rec_gbl_check_udf`, run after process())
                // raises `UDF_ALARM` with `udfs` severity, matching C's
                // `recGblSetSevr(pepid, UDF_ALARM, pepid->udfs)`.
                //
                // `update_monitors()` is deliberately NOT called here:
                // C's early `return(0)` skips `monitor()`, so the
                // previous-value fields (`pp`/`ip`/`dp`/...) and the
                // `mlst`/`alst` deadband baselines must NOT advance
                // while the record is undefined.
                //
                // C `return(0)` is reached before `recGblFwdLink` and
                // the `do_pid` output write. The Rust framework drives
                // the OUTL write (`multi_output_links`) and FLNK; flag
                // this cycle so `multi_output_links` and
                // `should_fire_forward_link` suppress them — otherwise
                // a stale OVAL would be pushed to the OUTL target.
                self.device_did_compute = false;
                self.compute_skipped = true;
                return Ok(ProcessOutcome::complete());
            }
        }

        if !self.device_did_compute {
            crate::device_support::epid_soft::EpidSoftDeviceSupport::do_pid(self);
        }
        self.device_did_compute = false; // Reset for next cycle

        // Alarm evaluation is NOT done here. The framework invokes the
        // `Record::check_alarms` trait hook (below) after `process()`,
        // which is where the computed severity is applied to SEVR/STAT
        // via `recGblSetSevr`. Calling the inherent `check_alarms` here
        // would advance `lalm` an extra time and double-step the
        // hysteresis state, so it is deliberately omitted.
        self.update_monitors();

        // Device support actions are now merged by the framework
        let actions = Vec::new();
        Ok(ProcessOutcome::complete_with(actions))
    }

    /// Per-record alarm hook — C `epidRecord.c::checkAlarms`.
    ///
    /// The framework calls this after `process()`; it computes the
    /// HIHI/HIGH/LOW/LOLO condition (with `lalm` hysteresis) via the
    /// inherent [`EpidRecord::check_alarms`] and applies the result to
    /// the record's pending alarm state with `recGblSetSevr`. That
    /// accumulates into `nsta`/`nsev` (raise-only / maximize-severity),
    /// which the framework later transfers to `STAT`/`SEVR` via
    /// `recGblResetAlarms`. Returning `None` raises nothing, so a value
    /// that stays inside the limits leaves the record un-alarmed and a
    /// held value does not re-fire.
    fn check_alarms(&mut self, common: &mut CommonFields) {
        // C `devEpidSoft.c:110-112` / `devEpidSoftCallback.c:115-117`:
        // a CONSTANT `INP` link means "nothing to control" — raise
        // SOFT_ALARM/INVALID_ALARM. `do_pid` set `inp_constant` and
        // skipped the compute; apply the severity here (the framework
        // calls this hook after `process()`).
        if self.inp_constant {
            recgbl::rec_gbl_set_sevr(common, alarm_status::SOFT_ALARM, AlarmSeverity::Invalid);
        }
        if let Some((stat, sevr, alev)) = EpidRecord::check_alarms(self) {
            // C `aiRecord.c:403-406`: `if (recGblSetSevr(...)) prec->lalm = alev;`
            // — the LALM update is gated on `recGblSetSevr` returning TRUE,
            // i.e. on the alarm actually raising the pending severity.
            // `rec_gbl_set_sevr` is raise-only and returns nothing, so detect
            // the raise by observing whether `nsev` increased across the call.
            let before = common.nsev;
            recgbl::rec_gbl_set_sevr(common, stat, sevr);
            if common.nsev != before {
                self.lalm = alev;
            }
        }
    }

    fn get_field(&self, name: &str) -> Option<EpicsValue> {
        match name {
            "VAL" => Some(EpicsValue::Double(self.val)),
            "SMSL" => Some(EpicsValue::Short(self.smsl)),
            "STPL" => Some(EpicsValue::String(self.stpl.clone())),
            "INP" => Some(EpicsValue::String(self.inp.clone())),
            "OUTL" => Some(EpicsValue::String(self.outl.clone())),
            "TRIG" => Some(EpicsValue::String(self.trig.clone())),
            "TVAL" => Some(EpicsValue::Double(self.tval)),
            "CVAL" => Some(EpicsValue::Double(self.cval)),
            "CVLP" => Some(EpicsValue::Double(self.cvlp)),
            "OVAL" => Some(EpicsValue::Double(self.oval)),
            "OVLP" => Some(EpicsValue::Double(self.ovlp)),
            "KP" => Some(EpicsValue::Double(self.kp)),
            "KI" => Some(EpicsValue::Double(self.ki)),
            "KD" => Some(EpicsValue::Double(self.kd)),
            "P" => Some(EpicsValue::Double(self.p)),
            "PP" => Some(EpicsValue::Double(self.pp)),
            "I" => Some(EpicsValue::Double(self.i)),
            "IP" => Some(EpicsValue::Double(self.ip)),
            "D" => Some(EpicsValue::Double(self.d)),
            "DP" => Some(EpicsValue::Double(self.dp)),
            "ERR" => Some(EpicsValue::Double(self.err)),
            "ERRP" => Some(EpicsValue::Double(self.errp)),
            "DT" => Some(EpicsValue::Double(self.dt)),
            "DTP" => Some(EpicsValue::Double(self.dtp)),
            "MDT" => Some(EpicsValue::Double(self.mdt)),
            "FMOD" => Some(EpicsValue::Short(self.fmod)),
            "FBON" => Some(EpicsValue::Short(self.fbon)),
            "FBOP" => Some(EpicsValue::Short(self.fbop)),
            "ODEL" => Some(EpicsValue::Double(self.odel)),
            "PREC" => Some(EpicsValue::Short(self.prec)),
            "EGU" => Some(EpicsValue::String(self.egu.clone())),
            "HOPR" => Some(EpicsValue::Double(self.hopr)),
            "LOPR" => Some(EpicsValue::Double(self.lopr)),
            "DRVH" => Some(EpicsValue::Double(self.drvh)),
            "DRVL" => Some(EpicsValue::Double(self.drvl)),
            "HIHI" => Some(EpicsValue::Double(self.hihi)),
            "LOLO" => Some(EpicsValue::Double(self.lolo)),
            "HIGH" => Some(EpicsValue::Double(self.high)),
            "LOW" => Some(EpicsValue::Double(self.low)),
            "HHSV" => Some(EpicsValue::Short(self.hhsv)),
            "LLSV" => Some(EpicsValue::Short(self.llsv)),
            "HSV" => Some(EpicsValue::Short(self.hsv)),
            "LSV" => Some(EpicsValue::Short(self.lsv)),
            "HYST" => Some(EpicsValue::Double(self.hyst)),
            "LALM" => Some(EpicsValue::Double(self.lalm)),
            "ADEL" => Some(EpicsValue::Double(self.adel)),
            "MDEL" => Some(EpicsValue::Double(self.mdel)),
            "ALST" => Some(EpicsValue::Double(self.alst)),
            "MLST" => Some(EpicsValue::Double(self.mlst)),
            _ => None,
        }
    }

    fn put_field(&mut self, name: &str, value: EpicsValue) -> CaResult<()> {
        match name {
            "VAL" => match value {
                EpicsValue::Double(v) => {
                    self.val = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "SMSL" => match value {
                EpicsValue::Short(v) => {
                    self.smsl = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "STPL" => match value {
                EpicsValue::String(v) => {
                    self.stpl = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "INP" => match value {
                EpicsValue::String(v) => {
                    self.inp = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "OUTL" => match value {
                EpicsValue::String(v) => {
                    self.outl = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "TRIG" => match value {
                EpicsValue::String(v) => {
                    self.trig = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "TVAL" => match value {
                EpicsValue::Double(v) => {
                    self.tval = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "KP" => match value {
                EpicsValue::Double(v) => {
                    self.kp = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "KI" => match value {
                EpicsValue::Double(v) => {
                    self.ki = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "KD" => match value {
                EpicsValue::Double(v) => {
                    self.kd = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "I" => match value {
                EpicsValue::Double(v) => {
                    self.i = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "IP" => match value {
                EpicsValue::Double(v) => {
                    self.ip = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "DT" => match value {
                EpicsValue::Double(v) => {
                    self.dt = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "MDT" => match value {
                EpicsValue::Double(v) => {
                    self.mdt = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "FMOD" => match value {
                EpicsValue::Short(v) => {
                    self.fmod = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "FBON" => match value {
                EpicsValue::Short(v) => {
                    self.fbon = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "ODEL" => match value {
                EpicsValue::Double(v) => {
                    self.odel = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "PREC" => match value {
                EpicsValue::Short(v) => {
                    self.prec = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "EGU" => match value {
                EpicsValue::String(v) => {
                    self.egu = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "HOPR" => match value {
                EpicsValue::Double(v) => {
                    self.hopr = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "LOPR" => match value {
                EpicsValue::Double(v) => {
                    self.lopr = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "DRVH" => match value {
                EpicsValue::Double(v) => {
                    self.drvh = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "DRVL" => match value {
                EpicsValue::Double(v) => {
                    self.drvl = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "HIHI" => match value {
                EpicsValue::Double(v) => {
                    self.hihi = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "LOLO" => match value {
                EpicsValue::Double(v) => {
                    self.lolo = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "HIGH" => match value {
                EpicsValue::Double(v) => {
                    self.high = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "LOW" => match value {
                EpicsValue::Double(v) => {
                    self.low = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "HHSV" => match value {
                EpicsValue::Short(v) => {
                    self.hhsv = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "LLSV" => match value {
                EpicsValue::Short(v) => {
                    self.llsv = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "HSV" => match value {
                EpicsValue::Short(v) => {
                    self.hsv = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "LSV" => match value {
                EpicsValue::Short(v) => {
                    self.lsv = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "HYST" => match value {
                EpicsValue::Double(v) => {
                    self.hyst = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "ADEL" => match value {
                EpicsValue::Double(v) => {
                    self.adel = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "MDEL" => match value {
                EpicsValue::Double(v) => {
                    self.mdel = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            // Read-only fields
            "CVAL" | "CVLP" | "OVAL" | "OVLP" | "P" | "PP" | "D" | "DP" | "ERR" | "ERRP"
            | "DTP" | "FBOP" | "LALM" | "ALST" | "MLST" => Err(CaError::ReadOnlyField(name.into())),
            _ => Err(CaError::FieldNotFound(name.into())),
        }
    }

    fn field_list(&self) -> &'static [FieldDesc] {
        FIELDS
    }

    fn as_any_mut(&mut self) -> Option<&mut dyn Any> {
        Some(self)
    }

    /// C `epidRecord.c` UDF ownership — see [`EpidRecord::value_undefined`].
    ///
    /// The framework's post-`process()` step runs
    /// `common.udf = value_is_undefined()` (gated on `clears_udf()`,
    /// left at its `true` default). Returning the epid-owned
    /// `value_undefined` — recomputed in `process()` from the two C
    /// clear-conditions — keeps `udf` TRUE for a supervisory / empty-
    /// STPL epid (so its UDF gate fires every cycle, as C does) and
    /// clears it only on a CONSTANT STPL or a successful closed-loop
    /// `dbGetLink(stpl)`.
    ///
    /// The default `value_is_undefined()` keys off `VAL` being NaN,
    /// which for an epid (`VAL` defaults to a finite `0.0`, never NaN)
    /// would wrongly clear `udf` after the first cycle — the bug this
    /// override fixes.
    fn value_is_undefined(&self) -> bool {
        self.value_undefined
    }

    fn set_device_did_compute(&mut self, did_compute: bool) {
        self.device_did_compute = did_compute;
    }

    /// C `epidRecord.c:195` reads `pepid->udf` at the top of
    /// `process()`. The framework owns `dbCommon.udf`; this hook
    /// captures it so `process()` can gate `do_pid` on it.
    fn set_process_context(&mut self, ctx: &ProcessContext) {
        self.udf = ctx.udf;
        self.dtyp.clear();
        self.dtyp.push_str(&ctx.dtyp);
    }

    /// C `devEpidSoftCallback.c:120-132` — the DB-type TRIG readback
    /// link write.
    ///
    /// `devEpidSoftCallback.c::do_pid`, within ONE process pass, does:
    ///   1. `if (ptriglink->type != CA_LINK)` →
    ///      `dbPutLink(ptriglink, DBR_DOUBLE, &pepid->tval, 1)`
    ///      (`devEpidSoftCallback.c:121-127`) — a synchronous write that
    ///      processes the triggered source chain;
    ///   2. `dbGetLink(&pepid->inp, DBR_DOUBLE, &pepid->cval, ...)`
    ///      (`devEpidSoftCallback.c:151`) — read CVAL from INP;
    ///   3. run the PID.
    ///
    /// So for a DB-type TRIG link the trigger write must land BEFORE
    /// this cycle's `INP -> CVAL` fetch. The framework resolves input
    /// links before `pre_process_actions`, so the TRIG write is emitted
    /// here, from `pre_input_link_actions`, which the framework runs
    /// strictly before the input-link fetch.
    ///
    /// Only the `devEpidSoftCallback` DSET (DTYP `"Epid Async Soft"`)
    /// drives the TRIG link — `devEpidSoft` (`devEpidSoft.c`) has no
    /// TRIG handling at all. The action is therefore gated on `dtyp`.
    ///
    /// The CA-type TRIG link is deliberately NOT emitted here: C
    /// `devEpidSoftCallback.c:133-147` cannot wait synchronously on a
    /// CA link, so it uses `dbCaPutLinkCallback` + `pact=TRUE` and
    /// re-processes on the callback. That two-pass path stays in
    /// `EpidSoftCallbackDeviceSupport::read` (`WriteDbLink` +
    /// `ReprocessAfter`).
    fn pre_input_link_actions(&mut self) -> Vec<ProcessAction> {
        if self.dtyp != "Epid Async Soft" {
            return Vec::new();
        }
        if link_field_type(&self.trig) == LinkType::Db {
            return vec![ProcessAction::WriteDbLink {
                link_field: "TRIG",
                value: EpicsValue::Double(self.tval),
            }];
        }
        Vec::new()
    }

    /// Framework report of which `multi_input_links` fetches produced a
    /// value this cycle — the analogue of C
    /// `RTN_SUCCESS(dbGetLink(&prec->stpl, ...))` (`epidRecord.c:191`).
    /// `STPL` is only ever in `multi_input_links` when
    /// `SMSL == closed_loop`; its presence here means the closed-loop
    /// setpoint fetch actually succeeded this cycle. A STPL that is
    /// empty, or a DB/CA link whose fetch failed, is absent — so
    /// `stpl_resolved` is reset to false and `udf` is not cleared.
    fn set_resolved_input_links(&mut self, resolved: &[&'static str]) {
        self.stpl_resolved = resolved.contains(&"STPL");
    }

    /// C `epidRecord.c:160-164` `init_record`: when `STPL` is a
    /// CONSTANT link holding a valid constant, `recGblInitConstantLink`
    /// seeds `VAL` from the constant and `udf` is cleared. The
    /// framework owns `dbCommon.udf`; this hook is its controlled
    /// access point. Runs once after `init_record`.
    ///
    /// For `SMSL == closed_loop` the framework also fetches `STPL` into
    /// `VAL` via `multi_input_links` every cycle; the constant seed
    /// here matters for the supervisory (`SMSL=0`) case and for the
    /// first cycle before any process.
    fn post_init_finalize_undef(&mut self, udf: &mut bool) -> CaResult<()> {
        let parsed = epics_base_rs::server::record::parse_link_v2(&self.stpl);
        if parsed.link_type() == LinkType::Constant {
            if let Some(EpicsValue::Double(v)) = parsed.constant_value() {
                self.val = v;
                *udf = false;
                self.value_undefined = false;
            }
        }
        Ok(())
    }

    fn put_field_internal(
        &mut self,
        name: &str,
        value: EpicsValue,
    ) -> epics_base_rs::error::CaResult<()> {
        // Bypass read-only checks for framework-internal writes (ReadDbLink).
        // This allows the framework to write to CVAL, OVAL, etc. from link resolution.
        match name {
            "CVAL" => match value {
                EpicsValue::Double(v) => {
                    self.cval = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "OVAL" => match value {
                EpicsValue::Double(v) => {
                    self.oval = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "P" => match value {
                EpicsValue::Double(v) => {
                    self.p = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "D" => match value {
                EpicsValue::Double(v) => {
                    self.d = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            "ERR" => match value {
                EpicsValue::Double(v) => {
                    self.err = v;
                    Ok(())
                }
                _ => Err(CaError::TypeMismatch(name.into())),
            },
            _ => self.put_field(name, value),
        }
    }

    fn multi_input_links(&self) -> &[(&'static str, &'static str)] {
        // INP -> CVAL is always resolved.
        // STPL -> VAL is only resolved when SMSL == closed_loop (1).
        // In supervisory mode (SMSL=0), the operator sets VAL directly
        // and STPL must not overwrite it.
        if self.smsl == 1 {
            // closed_loop: fetch setpoint from STPL into VAL
            static WITH_STPL: &[(&str, &str)] = &[("STPL", "VAL"), ("INP", "CVAL")];
            WITH_STPL
        } else {
            // supervisory: VAL is set by operator, don't fetch STPL
            static WITHOUT_STPL: &[(&str, &str)] = &[("INP", "CVAL")];
            WITHOUT_STPL
        }
    }

    fn multi_output_links(&self) -> &[(&'static str, &'static str)] {
        // C `epidRecord.c:195-202`: on a UDF-gated cycle `process()`
        // returns before `do_pid` writes the output — suppress the
        // OUTL->OVAL write so a stale OVAL is not pushed downstream.
        if self.compute_skipped {
            return &[];
        }
        // OUTL -> OVAL (output link)
        static LINKS: &[(&str, &str)] = &[("OUTL", "OVAL")];
        LINKS
    }

    fn should_fire_forward_link(&self) -> bool {
        // C `epidRecord.c:201` `return(0)` on a UDF-gated cycle is
        // reached before `recGblFwdLink` — no forward link this cycle.
        !self.compute_skipped
    }
}