epics-base-rs

Pure Rust implementation of EPICS Base — Channel Access protocol (client & server), IOC runtime, and iocsh.

No C dependencies. No libca. Just cargo build.

All binaries use the -rs suffix (e.g. caget-rs, caput-rs, softioc-rs) to avoid conflicts with the C EPICS tools.

Features

Client

caget-rs — read a PV value
caput-rs — write a PV value
camonitor-rs — subscribe to PV changes
cainfo-rs — display PV metadata
UDP name resolution and TCP virtual circuit
Extended header support for payloads > 64 KB

Server (Soft IOC)

softioc-rs binary — host PVs over Channel Access
20 record types: ai, ao, bi, bo, stringin, stringout, longin, longout, mbbi, mbbo, waveform, calc, calcout, fanout, dfanout, seq, sel, compress, histogram, sub
.db file loader with macro substitution
Record processing with full link chain traversal (INP → process → OUT → FLNK)
Periodic and event scan scheduling (Passive, Event, 10 Hz, 5 Hz, 2 Hz, 1 Hz, 0.5 Hz, 0.2 Hz, 0.1 Hz)
CALC engine (arithmetic, comparison, logic, ternary, math functions)
Monitor subscriptions with per-channel event delivery
Beacon emitter
Access security (ACF file parser, UAG/HAG/ASG rules, per-channel enforcement)
Autosave/restore (periodic save, atomic write, type-aware restore)
Device support trait for custom I/O drivers
Subroutine registry for sub records
IocApplication: st.cmd-style IOC lifecycle (C++ EPICS-compatible syntax)
iocsh: Interactive shell with C++ EPICS function-call syntax and $(VAR) substitution
Extended CA header for large payloads (> 64 KB) with 16 MB DoS limit

pvAccess (experimental)

pvaget-rs, pvaput-rs, pvamonitor-rs, pvainfo-rs — basic pvAccess client tools

What's New in v0.2

v0.2.0 — Declarative IOC Builder + Event Scheduler

Declarative IOC configuration — build IOCs entirely in Rust without .db files:

use epics_base_rs::server::ioc_app::IocApplication;
use epics_base_rs::server::records::ao::AoRecord;
use epics_base_rs::server::records::bi::BiRecord;

IocApplication::new()
    .record("TEMP", AoRecord::new(25.0))
    .record("INTERLOCK", BiRecord::new(0))
    .run()
    .await?;

ScanSchedulerV2 — event-driven scan scheduling with coalescing:

ScanEventKind: Periodic, IoIntr, Event, Delayed, Pini
submit_event() / submit_delayed() for external event injection
HashSet-based dedup within scan ticks — no duplicate processing

What's New in v0.3

v0.3.0 — Snapshot-Based Internal Model (GR/CTRL Metadata)

The problem: caget -d DBR_CTRL_DOUBLE <pv> returned zeroed units/limits/precision because GR/CTRL DBR types (21-34) were serialized identically to TIME — no metadata was populated.

The fix: A new Snapshot type serves as the single internal state representation, carrying value + alarm + timestamp + display/control/enum metadata. The CA serializer now encodes real metadata into GR/CTRL wire frames.

┌──────────────────────────────────────────────────────────┐
│                     Snapshot                             │
│  value: EpicsValue                                       │
│  alarm: AlarmInfo { status, severity }                   │
│  timestamp: SystemTime                                   │
│  display: Option<DisplayInfo>  ← EGU, PREC, HOPR/LOPR   │
│  control: Option<ControlInfo>  ← DRVH/DRVL               │
│  enums:   Option<EnumInfo>     ← ZNAM/ONAM, ZRST..FFST   │
└──────────────────────────────────────────────────────────┘
        │
        ▼  encode_dbr(dbr_type, &snapshot)
┌──────────────────────────────────────────────────────────┐
│  DBR_PLAIN (0-6)   → bare value bytes                    │
│  DBR_STS   (7-13)  → status + severity + value           │
│  DBR_TIME  (14-20) → status + severity + timestamp + val │
│  DBR_GR    (21-27) → sts + units + prec + limits + val   │  ← NEW: real data
│  DBR_CTRL  (28-34) → sts + units + prec + limits + ctrl  │  ← NEW: real data
│                       limits + val                        │
└──────────────────────────────────────────────────────────┘

Metadata populated per record type:

Record type	DisplayInfo	ControlInfo	EnumInfo
ai	EGU, PREC, HOPR/LOPR, alarm limits	HOPR/LOPR	—
ao	EGU, PREC, HOPR/LOPR, alarm limits	DRVH/DRVL	—
longin/longout	EGU, HOPR/LOPR, alarm limits	HOPR/LOPR or DRVH/DRVL	—
bi/bo	—	—	ZNAM, ONAM
mbbi/mbbo	—	—	ZRST..FFST (16 strings)

Before (v0.2):

$ caget -d DBR_CTRL_DOUBLE TEMP
    Units:
    Precision:    0
    Upper limit:  0
    Lower limit:  0

After (v0.3):

$ caget -d DBR_CTRL_DOUBLE TEMP
    Units:        degC
    Precision:    3
    Upper limit:  100
    Lower limit:  -50

Differences from C EPICS

The Snapshot model departs from C EPICS internals while preserving wire compatibility:

Aspect	C EPICS	epics-base-rs
Internal state	Metadata baked into each `dbCommon` / record struct as C struct fields; accessed via `dbAddr` pointer arithmetic	Metadata assembled on-demand into a `Snapshot` from `Record` trait + `CommonFields`; no pointer arithmetic
GR/CTRL serialization	`db_access.c` reads fields directly from the record's memory via `dbAddr` offsets into the flat C struct	`encode_dbr()` reads from `Snapshot.display` / `Snapshot.control` / `Snapshot.enums`; the serializer casts f64 → wire-native type (i16/f32/i32/f64)
Limit storage	Native type per record (e.g., `dbr_ctrl_short` stores `dbr_short_t` limits)	All limits stored as `f64` internally; cast to wire type at serialization time — matches the pattern used by C `dbFastLinkConv`
Enum strings	Fixed `char[MAX_ENUM_STATES][MAX_ENUM_STRING_SIZE]` in the record struct	`Vec<String>` in `EnumInfo`; padded to 16×26-byte slots at encoding time
Timestamp	`epicsTimeStamp` (EPICS epoch, 2×u32) stored in record	`SystemTime` stored in `CommonFields`; EPICS epoch conversion in serializer
Display precision	`PREC` field as `epicsInt16` in individual record structs	`precision: i16` inside `DisplayInfo`; only present for numeric record types
Per-request allocation	Zero allocation — `db_access.c` fills a pre-sized buffer from record pointers	`Snapshot` allocates `String` for EGU and `Vec<String>` for enums per request (<1μs; monitor path can cache)
Field dispatch	`dbAccess.c` switch on `dbAddr->field_type` + `dbAddr->no_elements`	`RecordInstance::snapshot_for_field()` matches on `record_type()` string

Wire compatibility: The exact same bytes appear on the wire as a C EPICS server would produce. A C client (caget, camonitor, cainfo) sees no difference.

Quick Start

cargo build --release

Run a Soft IOC

# Simple PVs
softioc-rs --pv TEMP:double:25.0 --pv MSG:string:hello

# With records
softioc-rs --record ai:SENSOR:0.0 --record bo:SWITCH:0

# From a .db file
softioc-rs --db my_ioc.db -m "P=TEST:,R=TEMP"

# Custom port
softioc-rs --db my_ioc.db --port 5065

Client Tools

# Read
caget-rs TEMP

# Write
caput-rs TEMP 42.0

# Monitor
camonitor-rs TEMP

Library Usage

Embedded Server

use epics_base_rs::server::CaServer;
use epics_base_rs::server::records::ao::AoRecord;

#[tokio::main]
async fn main() -> epics_base_rs::error::CaResult<()> {
    let server = CaServer::builder()
        .record("TEMP", AoRecord::new(25.0))
        .record("SETPOINT", AoRecord::new(0.0))
        .build()
        .await?;

    server.run().await
}

With .db File and Access Security

use std::collections::HashMap;
use epics_base_rs::server::CaServer;

#[tokio::main]
async fn main() -> epics_base_rs::error::CaResult<()> {
    let macros = HashMap::from([
        ("P".into(), "MY:".into()),
        ("R".into(), "TEMP".into()),
    ]);

    let server = CaServer::builder()
        .db_file("ioc.db", &macros)?
        .acf_file("security.acf")?
        .build()
        .await?;

    server.run().await
}

With Autosave

use std::path::PathBuf;
use std::time::Duration;
use epics_base_rs::server::CaServer;
use epics_base_rs::server::autosave::AutosaveConfig;
use epics_base_rs::server::records::ao::AoRecord;

#[tokio::main]
async fn main() -> epics_base_rs::error::CaResult<()> {
    let server = CaServer::builder()
        .record("TEMP", AoRecord::new(25.0))
        .autosave(AutosaveConfig {
            save_path: PathBuf::from("/tmp/ioc.sav"),
            period: Duration::from_secs(30),
            request_pvs: vec!["TEMP".into()],
        })
        .build()
        .await?;

    server.run().await
}

IocApplication (st.cmd-style IOC)

For driver developers building IOCs with custom device support — matching the C++ EPICS st.cmd startup pattern:

use epics_base_rs::server::ioc_app::IocApplication;
use epics_base_rs::server::iocsh::registry::*;

#[tokio::main]
async fn main() -> epics_base_rs::error::CaResult<()> {
    IocApplication::new()
        .register_startup_command(/* driver config command */)
        .register_device_support("myDriver", || Box::new(MyDeviceSupport::new()))
        .register_shell_command(/* runtime commands */)
        .startup_script("ioc/st.cmd")
        .run()
        .await
}

The startup script uses exact C++ EPICS syntax:

# ioc/st.cmd — identical to C++ EPICS
epicsEnvSet("PREFIX", "SIM1:")
epicsEnvSet("CAM",    "cam1:")
myDriverConfig("SIM1", 256, 256, 50000000)
dbLoadRecords("$(MY_DRIVER)/Db/myDriver.db", "P=$(PREFIX),R=$(CAM)")
iocInit()

IOC lifecycle (matches C++ EPICS):

Phase	Action	C++ Equivalent
Phase 1	Execute `st.cmd` (epicsEnvSet, dbLoadRecords, driver config)	st.cmd before `iocInit()`
Phase 2	Wire device support, restore autosave, start scan tasks	`iocInit()`
Phase 3	Interactive `epics>` shell (dbl, dbgf, dbpf, dbpr, ...)	iocsh REPL

IOC Module System (C++ `.dbd` → Rust Crates)

In C++ EPICS, .dbd files and Makefile control which modules (record types, device support, drivers) are included in an IOC. In Rust, this maps to Cargo's crate and feature system:

C++ EPICS	Rust Equivalent
`.dbd` files (module declarations)	`Cargo.toml` `[dependencies]`
`Makefile` `xxx_DBD +=` (add/remove modules)	Add/remove crate dependencies
`envPaths` (build-time path generation)	`DB_DIR` const via `CARGO_MANIFEST_DIR`
`< envPaths` in st.cmd	IOC binary `set_var()` at startup
`$(ADSIMDETECTOR)/db/file.template`	`$(SIM_DETECTOR)/Db/file.db`
`registrar()` / `device()` in `.dbd`	`register_device_support()` call
`#ifdef` conditional include	Cargo `features`

Project Structure Convention

Each driver crate follows the C++ EPICS layout:

my-driver/
  src/                  ← xxxApp/src/    (driver source)
    lib.rs
    driver.rs
    bin/my_ioc.rs       ← IOC binary
  Db/                   ← xxxApp/Db/     (database templates, ship with driver)
    myDriver.db
  ioc/                  ← iocBoot/iocXxx/ (deployment-specific startup)
    st.cmd

Db/ — database templates that belong to the driver (reusable across IOCs)
ioc/ — deployment-specific st.cmd and configuration
src/ — driver source code and IOC binary

Database Path Resolution

Each driver crate exports a DB_DIR constant with its absolute Db/ path:

// In driver crate's lib.rs
pub const DB_DIR: &str = concat!(env!("CARGO_MANIFEST_DIR"), "/Db");

The IOC binary sets environment variables at startup (like C++ envPaths):

// In IOC binary main()
unsafe { std::env::set_var("SIM_DETECTOR", sim_detector::DB_DIR.trim_end_matches("/Db")); }

Then st.cmd uses standard $(MODULE) references:

dbLoadRecords("$(SIM_DETECTOR)/Db/simDetector.db", "P=$(PREFIX),R=$(CAM)")

Client

use epics_base_rs::client::CaClient;

#[tokio::main]
async fn main() {
    let client = CaClient::new().await.unwrap();

    // Read
    let (_type, value) = client.caget("TEMP").await.unwrap();
    println!("TEMP = {value}");

    // Write
    client.caput("TEMP", "42.0").await.unwrap();
}

.db File Format

Standard EPICS database format with macro substitution:

record(ao, "$(P)$(R)") {
    field(DESC, "Temperature setpoint")
    field(VAL,  "25.0")
    field(HOPR, "100.0")
    field(LOPR, "0.0")
    field(HIHI, "90.0")
    field(HIGH, "70.0")
    field(LOW,  "5.0")
    field(LOLO, "2.0")
    field(HHSV, "MAJOR")
    field(HSV,  "MINOR")
    field(LSV,  "MINOR")
    field(LLSV, "MAJOR")
    field(SCAN, "1 second")
    field(INP,  "SIM:RAW")
    field(FLNK, "$(P)$(R):STATUS")
}

Access Security (ACF)

UAG(admins) { alice, bob }
HAG(control_room) { cr-pc1, cr-pc2 }

ASG(DEFAULT) {
    RULE(1, WRITE)
    RULE(1, READ)
}

ASG(RESTRICTED) {
    RULE(1, WRITE) { UAG(admins) HAG(control_room) }
    RULE(1, READ)
}

Record Types

Type	Description	Value Type
ai	Analog input	Double
ao	Analog output	Double
bi	Binary input	Enum (u16)
bo	Binary output	Enum (u16)
longin	Long input	Long (i32)
longout	Long output	Long (i32)
mbbi	Multi-bit binary input	Enum (u16)
mbbo	Multi-bit binary output	Enum (u16)
stringin	String input	String
stringout	String output	String
waveform	Array data	DoubleArray / LongArray / CharArray
calc	Calculation	Double
calcout	Calculation with output	Double (OVAL)
fanout	Forward link fanout	—
dfanout	Data fanout	Double
seq	Sequence	Double
sel	Select	Double
compress	Circular buffer / N-to-1 compression	DoubleArray
histogram	Signal histogram	LongArray
sub	Subroutine	Double

Architecture

epics-base-rs/
  src/
    client.rs          # CA client (caget-rs/caput-rs/camonitor-rs)
    protocol.rs        # CA protocol codec (normal + extended header)
    types.rs           # EpicsValue, DbFieldType, serialize_dbr, encode_dbr
    error.rs           # Error types
    channel.rs         # Channel abstraction (AccessRights, ChannelInfo)
    pva/               # pvAccess protocol (experimental)
    server/
      mod.rs           # CaServer, CaServerBuilder
      snapshot.rs      # Snapshot, AlarmInfo, DisplayInfo, ControlInfo, EnumInfo
      database.rs      # PvDatabase, link chain processing, CP link tracking
      record.rs        # Record trait, CommonFields, RecordInstance (shared infrastructure)
      tcp.rs           # TCP virtual circuit handler (per-client state, dispatch)
      udp.rs           # UDP search responder
      beacon.rs        # Beacon emitter (exponential backoff)
      scan.rs          # Periodic/event scan scheduler
      monitor.rs       # Subscription/monitor system (mpsc-based event delivery)
      calc_engine.rs   # Expression evaluator (CALC/CALCOUT fields)
      db_loader.rs     # .db file parser with macro substitution
      device_support.rs # DeviceSupport trait (init/read/write/I/O Intr)
      ioc_app.rs       # IocApplication (st.cmd lifecycle, 3-phase startup)
      iocsh/           # Interactive shell (C++ syntax tokenizer, commands)
      access_security.rs # ACF parser (UAG/HAG/ASG rules, per-channel enforcement)
      autosave.rs      # Save/restore (periodic save, atomic write, .req parsing)
      pv.rs            # ProcessVariable (simple PV, subscriber list)
      records/         # Per-record-type implementations (25 files)
  epics-macros/        # Proc macro for #[derive(EpicsRecord)]

Channel Access Protocol

The CA protocol (protocol.rs, types.rs) provides the wire format for all client-server communication. Every message starts with a 16-byte big-endian header:

Field	Size	Description
`cmmd`	u16	Command code (message type)
`postsize`	u16	Payload size (0xFFFF = extended)
`data_type`	u16	DBR type code
`count`	u16	Element count (0 = extended)
`cid`	u32	Channel ID or status
`available`	u32	Subscription ID or context

When payload exceeds 64 KB or element count exceeds 65535, the extended header format is used: postsize=0xFFFF, count=0, followed by 8 bytes of extended_postsize (u32) and extended_count (u32). Maximum payload: 16 MB (DoS limit).

Key message types:

Code	Name	Direction	Purpose
0	VERSION	Both	Protocol version negotiation
6	SEARCH	C→S (UDP)	PV name lookup
18	CREATE_CHAN	C→S	Open channel, get CID
15	READ_NOTIFY	C→S	Read PV value
19	WRITE_NOTIFY	C→S	Write PV value (with ack)
1	EVENT_ADD	Both	Subscribe to changes / deliver updates
2	EVENT_CANCEL	C→S	Unsubscribe
13	RSRV_IS_UP	S→C (UDP)	Beacon announcement
23	ECHO	Both	Connection keepalive
12	CLEAR_CHANNEL	C→S	Close channel

DBR types encode both the value type and metadata level:

Range	Level	Contents
0–6	PLAIN	Bare value
7–13	STS	+ alarm status/severity
14–20	TIME	+ EPICS timestamp
21–27	GR	+ units, precision, display/alarm limits
28–34	CTRL	+ control limits (DRVH/DRVL)

Monitor masks control which changes trigger subscription updates: DBE_VALUE (1), DBE_LOG (2), DBE_ALARM (4), DBE_PROPERTY (8).

CA Client

The client (client.rs, channel.rs) implements the CA consumer side:

Name resolution: UDP broadcast SEARCH to EPICS_CA_ADDR_LIST (default: broadcast on port 5064)
Connection: TCP virtual circuit to the server's advertised port
Channel creation: CREATE_CHAN with PV name → server assigns CID + reports native type, element count, access rights
I/O: READ_NOTIFY / WRITE_NOTIFY for one-shot read/write; EVENT_ADD for subscriptions
Cleanup: EVENT_CANCEL, CLEAR_CHANNEL, TCP close

The CaClient API wraps this lifecycle:

let client = CaClient::new().await?;
let (dbr_type, value) = client.caget("TEMP").await?;  // search + connect + read
client.caput("TEMP", "42.0").await?;                   // write with callback

CA Server

The server consists of three network components running as tokio tasks:

UDP search responder (udp.rs) — Listens on port 5064 (configurable via EPICS_CA_SERVER_PORT). Parses incoming SEARCH messages, checks PvDatabase::has_name(), and responds with SEARCH reply containing the server's TCP port.

Beacon emitter (beacon.rs) — Broadcasts RSRV_IS_UP on port 5065 with exponential backoff (20 ms → 15 s, doubling each step). Clients use beacons to detect new servers without re-searching.

TCP virtual circuit handler (tcp.rs) — Accepts connections and manages per-client state:

struct ClientState {
    channels: HashMap<u32, ChannelEntry>,        // CID → channel binding
    subscriptions: HashMap<u32, SubscriptionEntry>, // SUBID → active monitor
    channel_access: HashMap<u32, AccessLevel>,   // CID → computed ACF access
    hostname: String,                             // for ACF enforcement
    username: String,
}

The dispatch loop reads messages from the TCP stream and handles each command:

CREATE_CHAN → look up PV, allocate CID, compute access rights, reply with type info
READ_NOTIFY → build Snapshot from record/PV, encode to requested DBR type, reply
WRITE_NOTIFY → decode payload, put_field() on record, trigger process + links, reply
EVENT_ADD → create subscriber with mpsc channel, spawn monitor delivery task
EVENT_CANCEL → drop subscriber, close channel
ECHO → echo response (keepalive)

PvDatabase and Link Chains

PvDatabase (database.rs) is the central registry for all PVs and records:

struct PvDatabase {
    simple_pvs: HashMap<String, ProcessVariable>,
    records: HashMap<String, RecordInstance>,
    scan_index: HashMap<ScanType, BTreeSet<(i32, String)>>,  // PHAS-sorted
    cp_links: HashMap<String, Vec<String>>,                   // source → targets
}

PV name resolution parses "TEMP.EGU" into record name "TEMP" + field "EGU" (default field is "VAL"). Field values resolve through a 3-level priority: record-specific field → common field (SEVR, STAT, SCAN, etc.) → VAL fallback.

Link chain processing handles forward links (FLNK) and channel-process links (CP):

When a record is processed, process_record_with_links() follows FLNK to process downstream records in sequence, using a visited set to prevent cycles
CP links are tracked in cp_links: when a source PV changes, all target records are automatically processed

Timestamp source (TSE field): TSE=0 uses system clock, TSE=-1 uses device-provided time, TSE=-2 preserves the existing TIME field.

Record System: `record.rs` vs `records/`

The record system is split into two layers:

record.rs contains shared infrastructure used by all record types. It is intentionally a single file because these components are tightly coupled:

Section	Lines	Contents
Types & enums	1–170	`FieldDesc`, `AlarmSeverity`, `ScanType`, `AlarmStatus`, field metadata
`CommonFields`	173–269	Fields shared by every record: `VAL`, `NAME`, `DESC`, `SCAN`, `PINI`, alarm fields, etc.
Link parsing	271–406	`parse_link()`, CP/CPP/PP/MS modifiers, link chain resolution
`Record` trait	408–524	The trait all record types implement: `process()`, `read()`/`write()`, `special()`, `as_any_mut()`, `can_device_write()`
`RecordInstance`	527–1377	Core runtime (~850 lines): field get/put, alarm evaluation, process cycle, deadband, monitor subscriptions, snapshot generation
Tests	1379–end	Unit tests for all of the above

records/ contains one file per record type (e.g., ai.rs, ao.rs, bi.rs, motor.rs, …). Each file defines its type-specific fields and implements the Record trait. The #[derive(EpicsRecord)] proc macro generates the boilerplate (field descriptors, get/put dispatch) so that each record file focuses only on its unique processing logic.

This separation means adding a new record type never touches record.rs — you create a new file in records/, derive the macro, and implement Record.

Snapshot Model

Snapshot (snapshot.rs) is the single internal representation for PV state. It carries everything needed to produce any DBR wire type:

Snapshot {
    value: EpicsValue,
    alarm: AlarmInfo { status, severity },
    timestamp: SystemTime,
    display: Option<DisplayInfo>,   // EGU, PREC, HOPR/LOPR, alarm limits
    control: Option<ControlInfo>,   // DRVH/DRVL
    enums: Option<EnumInfo>,        // ZNAM/ONAM or ZRST..FFST
}

encode_dbr(dbr_type, &snapshot) serializes a Snapshot to any of the 35 DBR wire formats. All limits are stored internally as f64 and cast to the wire-native type (i16/f32/i32/f64) at serialization time.

Device Support

The DeviceSupport trait (device_support.rs) connects records to external I/O drivers:

trait DeviceSupport: Send + Sync {
    fn init(&mut self, record: &mut dyn Record) -> CaResult<()>;
    fn read(&mut self, record: &mut dyn Record) -> CaResult<()>;
    fn write(&mut self, record: &mut dyn Record) -> CaResult<()>;
    fn dtyp(&self) -> &str;
    fn io_intr_receiver(&mut self) -> Option<mpsc::Receiver<()>>;
    fn write_begin(&mut self, record: &mut dyn Record)
        -> CaResult<Option<Box<dyn WriteCompletion>>>;
}

Records with a DTYP field delegate their I/O to a matching DeviceSupport instance:

init(): Called once during iocInit (Phase 2). Can inject driver state into the record via as_any_mut() downcast.
read(): Called during record process when the record has an input link to the driver.
write(): Called when a CA client writes to the record (if can_device_write() returns true).
I/O Intr scanning: io_intr_receiver() returns an mpsc::Receiver<()>. The scan system processes the record each time the driver sends a signal.
Async writes: write_begin() submits the operation to a worker queue and returns a completion handle.

Scan System

The scan scheduler (scan.rs) drives periodic and event-based record processing:

Scan Type	Trigger
Passive	Only processed via links (FLNK, CP) or CA writes
I/O Intr	Device support signals via mpsc channel
Event	External event injection via `submit_event()`
10 Hz – 0.1 Hz	Periodic tokio tasks (100 ms – 10 s intervals)

At IOC startup:

Records with PINI=YES are processed once (respecting PHAS ordering)
Periodic scan tasks are spawned (one tokio task per rate)
I/O Intr receivers are collected from device support and monitored

Periodic scans use the scan_index (BTreeSet sorted by PHAS) for deterministic ordering. A visited set prevents infinite loops in link chain traversal.

Monitor/Subscription System

The monitor system (monitor.rs, pv.rs) delivers value change notifications to CA clients:

Record process → put_field() → notify_subscribers()
                                      │
                        ┌─────────────┼─────────────┐
                        ▼             ▼             ▼
                  Subscriber 1   Subscriber 2   Subscriber N
                  (mpsc::tx)     (mpsc::tx)     (mpsc::tx)
                        │             │             │
                        ▼             ▼             ▼
                  monitor task   monitor task   monitor task
                  (encode+send)  (encode+send)  (encode+send)

Each Subscriber holds a mask (DBE_VALUE | DBE_ALARM | ...), requested DBR type, and an mpsc sender. When a PV value changes, notify_subscribers() sends a MonitorEvent (containing the full Snapshot) to each subscriber's channel. A dedicated tokio task per subscriber encodes the snapshot and writes the EVENT_ADD response to the TCP connection. Closed subscribers are automatically removed on the next notify cycle.

IocApplication (st.cmd Lifecycle)

IocApplication (ioc_app.rs) provides the C EPICS-compatible IOC startup pattern:

Phase	Thread	Action
Phase 1	std::thread	Execute st.cmd: `epicsEnvSet`, `dbLoadRecords`, driver config commands
Phase 2	tokio	iocInit: wire device support → records, start scan tasks, start CA server
Phase 3	std::thread	Interactive `epics>` REPL for runtime inspection

Phase 1 runs on a blocking std::thread because iocsh commands use Handle::block_on() to call async database methods synchronously. Phase 2 and the CA server run on the tokio runtime. Phase 3 spawns another blocking thread for the interactive REPL.

Key builder methods:

register_startup_command(CommandDef) — commands available during Phase 1
register_shell_command(CommandDef) — commands available during Phase 3
register_device_support(dtyp, factory) — static DTYP → factory mapping
register_dynamic_device_support(factory) — chained fallback factory (new factory tries first, falls back to existing)
startup_script(path) — path to st.cmd file

iocsh (Interactive Shell)

The iocsh (iocsh/) provides a command-line interface with C++ EPICS-compatible syntax:

# C++ syntax (primary)
epicsEnvSet("PREFIX", "SIM1:")
dbLoadRecords("$(MY_DRIVER)/Db/sim.db", "P=$(PREFIX)")
myDriverConfig("SIM1", 256, 256)

# Macro substitution
$(VAR)          # environment variable
$(VAR=default)  # with default value

The tokenizer handles parentheses, comma-separated arguments, quoted strings, and $(MACRO) expansion from environment variables. CommandContext provides the sync→async bridge: block_on() runs futures from the REPL thread, runtime_handle() gives access to the tokio handle for spawning tasks.

Built-in shell commands: dbl (list records), dbgf (get field), dbpf (put field), dbpr (print record), help.

Database Loader

The db loader (db_loader.rs) parses .db / .template files:

record(ao, "$(P)$(R)") {
    field(DESC, "Temperature")
    field(VAL,  "25.0")
    field(SCAN, "1 second")
    field(FLNK, "$(P)STATUS")
}

Parsing flow:

Read file, apply macro substitution ($(NAME), ${NAME}, $(NAME=default))
Parse into DbRecordDef list (record type, name, fields)
For each definition, create record via built-in type map or RecordFactory registry
Apply fields via put_field() and common fields via put_common_field()
Two-phase init: init_record(0) then init_record(1)
Register in PvDatabase

External crates can register custom record types via register_record_type() to override built-in stubs (e.g., asyn-rs registers asynRecord).

Access Security

The ACF system (access_security.rs) provides per-channel read/write control:

UAG(admins) { alice, bob }
HAG(control_room) { cr-pc1, cr-pc2 }
ASG(RESTRICTED) {
    RULE(1, WRITE) { UAG(admins) HAG(control_room) }
    RULE(1, READ)
}

UAG (User Access Group): named set of usernames
HAG (Host Access Group): named set of hostnames
ASG (Access Security Group): collection of rules; records reference an ASG via the ASG field

Access check: for each rule in the ASG, if the client's username matches a UAG member and hostname matches a HAG member, grant the rule's level (Read or ReadWrite). No ACF configured = all channels get full access.

Autosave

The autosave system (autosave.rs) persists PV values across IOC restarts:

Save: Periodically writes specified PVs to a file (one PV_NAME value per line), using atomic write (temp file + rename) for crash safety
Restore: On IOC startup, reads the save file and calls put_field() for each entry before records are initialized
Request files: .req format lists PVs to save, with $(MACRO) support
Backup: Optional timestamped rolling backups

CALC Engine

The expression evaluator (calc_engine.rs) powers calc and calcout records. Supports the full C EPICS CALC syntax:

Variables: A through L (12 inputs from INPA–INPL links)
Arithmetic: +, -, *, /, %
Comparison: <, <=, >, >=, =, !=, # (not equal)
Logic: &&, ||, !, ~ (bitwise NOT), |, &, >>, <<
Ternary: ? : (C-style conditional)
Math functions: ABS, SQR, SQRT, MIN, MAX, CEIL, FLOOR, LOG, LOGE, EXP, SIN, COS, TAN, ASIN, ACOS, ATAN, ATAN2, NINT, ISNAN, ISINF, FINITE, RANDOM

Data Flow: CA Read Request

Client                    tcp.rs                     record.rs / pv.rs          types.rs
  │                         │                             │                        │
  │  CA_PROTO_READ_NOTIFY   │                             │                        │
  │ (dbr_type=DBR_CTRL_DOUBLE)                            │                        │
  │────────────────────────>│                             │                        │
  │                         │  get_full_snapshot()        │                        │
  │                         │────────────────────────────>│                        │
  │                         │                             │  snapshot_for_field()  │
  │                         │                             │  ┌─ resolve_field()    │
  │                         │                             │  ├─ populate_display() │
  │                         │                             │  ├─ populate_control() │
  │                         │                             │  └─ populate_enum()    │
  │                         │       Snapshot              │                        │
  │                         │<────────────────────────────│                        │
  │                         │                             │                        │
  │                         │  encode_dbr(34, &snapshot)  │                        │
  │                         │────────────────────────────────────────────────────>│
  │                         │                             │   encode_ctrl()        │
  │                         │                             │   ┌─ status/severity   │
  │                         │                             │   ├─ prec + units      │
  │                         │       wire bytes            │   ├─ 8 limits (f64)    │
  │                         │<────────────────────────────────────────────────────│
  │    CA response          │                             │   └─ value             │
  │<────────────────────────│                             │                        │

Testing

cargo test

286 tests covering protocol encoding, wire format golden packets, snapshot generation, GR/CTRL metadata serialization, record processing, link chains, calc engine, .db parsing, access security, autosave, iocsh, declarative IOC builder, and event scheduling.

Requirements

Rust 1.70+
tokio runtime

License

MIT

epics-base-rs 0.4.1

epics-base-rs

Features

Client

Server (Soft IOC)

pvAccess (experimental)

What's New in v0.2

v0.2.0 — Declarative IOC Builder + Event Scheduler

What's New in v0.3

v0.3.0 — Snapshot-Based Internal Model (GR/CTRL Metadata)

Differences from C EPICS

Quick Start

Run a Soft IOC

Client Tools

Library Usage

Embedded Server

With .db File and Access Security

With Autosave

IocApplication (st.cmd-style IOC)

IOC Module System (C++ .dbd → Rust Crates)

Project Structure Convention

Database Path Resolution

Client

.db File Format

Access Security (ACF)

Record Types

Architecture

Channel Access Protocol

CA Client

CA Server

PvDatabase and Link Chains

Record System: record.rs vs records/

Snapshot Model

Device Support

Scan System

Monitor/Subscription System

IocApplication (st.cmd Lifecycle)

iocsh (Interactive Shell)

Database Loader

Access Security

Autosave

CALC Engine

Data Flow: CA Read Request

Testing

Requirements

License

IOC Module System (C++ `.dbd` → Rust Crates)

Record System: `record.rs` vs `records/`