6.3 Read 32 temperature channels

Run the Chapter 4 32-channel temperature database through iocsh.bash without the compiled jeonglee_Demo executable, and group representative channels into one structured pvAccess (PVA) object with dbLoadGroup. You inspect both individual Channel Access (CA) and PVA records and a composite QSRV2 group process variable (PV) served by the Input/Output Controller (IOC).

Prerequisites

Complete Run a 32-channel temperature simulator and Generate and load 32 channel records.
Confirm that db/TC-32.db and db/tc32.proto exist in jeonglee_Demo/ with $(P)$(R) macros intact after the Chapter 4 exercises.
Stop any IOC or simulator listening on port 9399.
Activate the matching EPICS-env 1.5.0 tree in the IOC and client terminals.

Open three Bash terminals on the same host with these roles and settings:

Terminal	Role	Working directory	Environment
Terminal 1	TC-32 emulator (`9399`)	`jeonglee_Demo/simulator/`	No EPICS environment required
Terminal 2	IOC (`iocsh.bash`)	`jeonglee_Demo/` then `jeonglee_Demo/loader_tc32/`	`source "$TREE/setEpicsEnv.bash"`
Terminal 3	CA and PVA client	Any directory	`source "$TREE/setEpicsEnv.bash"`, `export EPICS_CA_AUTO_ADDR_LIST=NO EPICS_CA_ADDR_LIST=127.0.0.1`, `export EPICS_PVA_AUTO_ADDR_LIST=NO EPICS_PVA_ADDR_LIST=127.0.0.1`

In each EPICS terminal, set TREE to your installation path from lesson 1.1 (such as "$HOME/epics/1.5.0/debian-13/7.0.10") before running source "$TREE/setEpicsEnv.bash".

Prepare the database, group JSON, and startup

In terminal 2 from your jeonglee_Demo/ application directory, copy the generated database and protocol into a loader directory:
```
mkdir -p loader_tc32
cp db/TC-32.db db/tc32.proto loader_tc32/
cd loader_tc32
```
In terminal 2 inside loader_tc32/, save this QSRV2 group definition as tc32_group.json:
```
{
    "$(P)$(R)Summary": {
        "+id": "training:nt/TC32Summary:1.0",

        "device.model": {"+type": "const",  "+const": "TC-32"},

        "ch01":         {"+type": "scalar", "+channel": "$(P)$(R)CH01.VAL"},
        "ch16":         {"+type": "scalar", "+channel": "$(P)$(R)CH16.VAL"},
        "ch32":         {"+type": "scalar", "+channel": "$(P)$(R)CH32.VAL", "+trigger": "*"}
    }
}
```
Each mapping key configures how QSRV2 assembles LOADER:TC32:Summary:
- "+id" assigns the top-level PVA structure identifier training:nt/TC32Summary:1.0.
- "+type": "const" with "+const": "TC-32" publishes a constant device.model string field without an underlying EPICS record.
- "+type": "scalar" embeds each selected channel’s NTScalar value, alarm, timestamp, and display metadata from $(P)$(R)CH*.VAL.
- "+trigger": "*" on ch32 publishes an atomic subscription update across all group fields when channel 32 finishes a streaming sweep. Omitting +putorder keeps the group read-only.

In terminal 2 inside loader_tc32/, save this startup file as st.cmd:

on error break
module StreamDevice

epicsEnvSet("STREAM_PROTOCOL_PATH", ".")
drvAsynIPPortConfigure("TC32", "127.0.0.1:9399", 0, 0, 0)
asynOctetSetInputEos("TC32", 0, "\n")
asynOctetSetOutputEos("TC32", 0, "\n")
dbLoadRecords("TC-32.db", "P=LOADER:,R=TC32:,PORT=TC32")
dbLoadGroup("tc32_group.json", "P=LOADER:,R=TC32:")
iocInit()

softIocPVX links pvxs with QSRV2 enabled by default, so dbLoadGroup needs no extra module directive in st.cmd.

In terminal 2 inside loader_tc32/, preview the generated startup before launching the IOC:
```
iocsh.bash -n st.cmd
```

Read scalar channels and the structured group

In terminal 1 inside jeonglee_Demo/simulator/, start the TC-32 emulator on port 9399:
```
./tc32_emulator.bash --port 9399
```
In terminal 2 inside loader_tc32/, start the IOC:
```
iocsh.bash st.cmd
```
At the iocsh prompt in terminal 2, list the registered QSRV2 group definition:
```
pvxgl(1, "*")
```
pvxgl reports the group name, atomic delivery mode, and four mapped members (device.model, ch01, ch16, and ch32):
```
LOADER:TC32:Summary
  Atomic Get/Put:yes Atomic Members:4
```

In terminal 3, direct CA and PVA searches to loopback:

export EPICS_CA_AUTO_ADDR_LIST=NO EPICS_CA_ADDR_LIST=127.0.0.1
export EPICS_PVA_AUTO_ADDR_LIST=NO EPICS_PVA_ADDR_LIST=127.0.0.1

In terminal 3, read three scalar temperature channels and channel 01 metadata through CA:

caget LOADER:TC32:CH01 LOADER:TC32:CH16 LOADER:TC32:CH32
caget LOADER:TC32:CH01.EGU LOADER:TC32:CH01.DESC LOADER:TC32:CH01.SEVR

Live temperatures fall between 10 and 90 degrees Celsius with NO_ALARM severity:

LOADER:TC32:CH01               77.1052
LOADER:TC32:CH16               86.3493
LOADER:TC32:CH32               76.6859
LOADER:TC32:CH01.EGU           Celsius
LOADER:TC32:CH01.DESC          TC temperature at Channel 01
LOADER:TC32:CH01.SEVR          NO_ALARM

In terminal 3, read channel 01 as an individual PVA NTScalar record:

pvxget LOADER:TC32:CH01

pvxget prints the value, alarm, timestamp, and engineering units from the same ai record:

LOADER:TC32:CH01
    value double = 76.4265
    alarm.severity int32_t = 0
    alarm.status int32_t = 0
    alarm.message string = ""
    timeStamp.secondsPastEpoch int64_t = 1794422277
    timeStamp.nanoseconds int32_t = 691465958
    timeStamp.userTag int32_t = 0
    display.limitLow double = 0
    display.limitHigh double = 0
    display.description string = "TC temperature at Channel 01"
    display.units string = "Celsius"
    display.precision int32_t = 0
    display.form.index int32_t = 0
    display.form.choices string[] = {7}["Default", "String", "Binary", "Decimal", "Hex", "Exponential", "Engineering"]
    control.limitLow double = 0
    control.limitHigh double = 0
    valueAlarm.lowAlarmLimit double = nan
    valueAlarm.lowWarningLimit double = nan
    valueAlarm.highWarningLimit double = nan
    valueAlarm.highAlarmLimit double = nan

In terminal 3, read the composite LOADER:TC32:Summary group PV in a single PVA request:

pvxget LOADER:TC32:Summary

One atomic PVA read returns ch01, ch16, ch32, and device.model together from the server:

LOADER:TC32:Summary
    record._options.atomic bool = true
    ch01.value double = 76.4265
    ch01.alarm.severity int32_t = 0
    ch01.alarm.status int32_t = 0
    ch01.alarm.message string = ""
    ch01.timeStamp.secondsPastEpoch int64_t = 1794422277
    ch01.timeStamp.nanoseconds int32_t = 691465958
    ch01.timeStamp.userTag int32_t = 0
    ch01.display.limitLow double = 0
    ch01.display.limitHigh double = 0
    ch01.display.description string = "TC temperature at Channel 01"
    ch01.display.units string = "Celsius"
    ch01.display.precision int32_t = 0
    ch01.display.form.index int32_t = 0
    ch01.display.form.choices string[] = {7}["Default", "String", "Binary", "Decimal", "Hex", "Exponential", "Engineering"]
    ch01.control.limitLow double = 0
    ch01.control.limitHigh double = 0
    ch01.valueAlarm.lowAlarmLimit double = nan
    ch01.valueAlarm.lowWarningLimit double = nan
    ch01.valueAlarm.highWarningLimit double = nan
    ch01.valueAlarm.highAlarmLimit double = nan
    ch16.value double = 86.5753
    ch16.alarm.severity int32_t = 0
    ch16.alarm.status int32_t = 0
    ch16.alarm.message string = ""
    ch16.timeStamp.secondsPastEpoch int64_t = 1794422277
    ch16.timeStamp.nanoseconds int32_t = 729144531
    ch16.timeStamp.userTag int32_t = 0
    # Repeated display, control, and valueAlarm fields omitted for ch16 and ch32
    ch32.value double = 77.3631
    ch32.alarm.severity int32_t = 0
    ch32.alarm.status int32_t = 0
    ch32.alarm.message string = ""
    ch32.timeStamp.secondsPastEpoch int64_t = 1794422277
    ch32.timeStamp.nanoseconds int32_t = 688521675
    ch32.timeStamp.userTag int32_t = 0
    device.model string = "TC-32"

Verification

In terminal 3, read all 32 scalar channels once to confirm every record receives live stream updates between 10 and 90:
```
for ch in {01..32}; do caget -t "LOADER:TC32:CH$ch"; done
```

In terminal 3, inspect the published PVA type identifier on LOADER:TC32:Summary:

pvxinfo LOADER:TC32:Summary | head -n 3

The structure header shows the custom +id contract:

LOADER:TC32:Summary from 127.0.0.1:43259
struct "training:nt/TC32Summary:1.0" {
    struct {

In terminal 3, subscribe to three scalar channels with camonitor to verify continuous updates:
```
camonitor LOADER:TC32:CH01 LOADER:TC32:CH16 LOADER:TC32:CH32
```
Stop camonitor in terminal 3 with Ctrl+C, stop tc32_emulator.bash in terminal 1 with Ctrl+C, and then enter exit in terminal 2.

Keyboard shortcuts

ALS-U EPICS Environment Training

6.3 Read 32 temperature channels

Prerequisites

Prepare the database, group JSON, and startup

Read scalar channels and the structured group

Verification