feat(kpa): the Elecraft KPA500 / KPA1500 protocol, decoded and pinned

One package for both amplifiers: they share the Elecraft command set — a
caret, letters, a semicolon, case-insensitive in and upper case out — the
same family as the K3/K4 panel. What differs is the transport and which
commands exist, not the grammar.

Everything here comes from the KPA1500 Programming Reference, and the
document's own examples ARE the test:

  ^WS1204 014;  1204 W and SWR 1.4:1 — power and SWR in one exchange
  ^VI513 061;   51.3 V and 61 A — volts in tenths, amps whole
  ^FL91;        HEX, and 0x91 is 'antenna not connected?'

That last one is why the parsing is pinned rather than eyeballed: read as
decimal, 90 and 91 become 144 and 145 and match nothing, so an amplifier
shut down by high reflected power would report a fault OpsLog could not
name. SWR in tenths is confirmed by the reference too — 'expressed in
tenths, 123 is 12.3:1' — where it had only been inferred from Hamlib.

The client is question-and-answer under one lock, never two questions in
flight: the reference states there is no flow control and that commands
are paced by waiting for the reply. Fast cycle four times a second for
power, SWR and the fault; the rest once a second.

Faults are named in the operator's terms — 'the ATU found no match', not
'fault 92' — and an unknown code from a newer firmware still says
something rather than nothing.

Not wired to the app yet, and two commands are deliberately absent: ^TX
makes the amplifier transmit from software, and ^ON0 cuts the main
supplies with Wake-on-LAN as the way back. Neither belongs on a poll loop
or behind a button that can be pressed by accident.
This commit is contained in:
2026-08-26 17:43:32 +02:00
parent 949b92d7e7
commit 55a643d9a4
4 changed files with 695 additions and 0 deletions
+374
View File
@@ -0,0 +1,374 @@
package kpa
// The client: one connection, strict question-and-answer, a cached status.
//
// Shaped like internal/acom and internal/spe so a third amplifier is the same
// thing to read — but the traffic is the opposite kind. Those two are told to
// stream and are then listened to; this one is asked, and answers. The
// reference is explicit that there is no flow control and that commands are
// paced by waiting for the previous reply, so nothing here ever has two
// questions outstanding.
import (
"bufio"
"fmt"
"io"
"net"
"strings"
"sync"
"time"
"go.bug.st/serial"
"hamlog/internal/applog"
)
const (
dialTimeout = 5 * time.Second
ioTimeout = 2 * time.Second
// pollInterval is the fast cycle: forward power, SWR, and whether a fault has
// appeared. Four times a second is enough for a bar that is read while
// talking, and it is four round trips a second on a link with no flow
// control — faster buys nothing and costs the set commands their latency.
pollInterval = 250 * time.Millisecond
// slowEvery is how many fast cycles pass between the readings that do not
// move: mode, band, temperature, supply. Once a second.
slowEvery = 4
)
// Status is what the panel polls.
type Status struct {
Connected bool `json:"connected"`
Transport string `json:"transport"` // "serial" | "tcp"
Model string `json:"model,omitempty"`
LastError string `json:"last_error,omitempty"`
// PowerOn is the main supplies (^ON), Operate is OPERATE vs STANDBY (^OS).
// They are different questions: an amplifier can be switched on and in
// standby, which is the normal state between overs.
PowerOn bool `json:"power_on"`
Operate bool `json:"operate"`
FwdW int `json:"fwd_w"`
SWR float64 `json:"swr"`
VoltV float64 `json:"volt_v"`
CurA int `json:"cur_a"`
TempC int `json:"temp_c"`
Band string `json:"band,omitempty"`
// Tuning is the ATU mid-cycle (^TP), so a panel can say so rather than
// showing a wild SWR and a power reading nobody should act on.
Tuning bool `json:"tuning"`
// Fault is the current fault code and its meaning. A fault puts the
// amplifier in STANDBY by itself, so it is the first thing to show.
FaultCode int `json:"fault_code"`
FaultText string `json:"fault_text,omitempty"`
}
// Config selects the model and how to reach it.
type Config struct {
Model string // "KPA500" | "KPA1500"
Transport string // "serial" | "tcp"
ComPort string // serial
Baud int // serial: 4800…230400, set on the amplifier and not negotiated
Host string // tcp (KPA1500 only)
Port int // tcp, default 1500
}
type Client struct {
cfg Config
mu sync.Mutex // serialises the connection: one question at a time
conn io.ReadWriteCloser
rd *bufio.Reader
statusMu sync.RWMutex
status Status
stop chan struct{}
running bool
}
// New builds a client. Nothing is opened until Start.
func New(cfg Config) *Client {
if cfg.Baud <= 0 {
cfg.Baud = 38400
}
if cfg.Port <= 0 {
cfg.Port = 1500
}
if strings.TrimSpace(cfg.Model) == "" {
cfg.Model = "KPA1500"
}
c := &Client{cfg: cfg, stop: make(chan struct{})}
c.status.Transport = cfg.Transport
c.status.Model = strings.ToUpper(strings.TrimSpace(cfg.Model))
return c
}
func (c *Client) Start() error {
if c.running {
return nil
}
c.running = true
go c.pollLoop()
return nil
}
func (c *Client) Stop() {
if !c.running {
return
}
c.running = false
close(c.stop)
c.mu.Lock()
c.dropLocked()
c.mu.Unlock()
}
func (c *Client) GetStatus() Status {
c.statusMu.RLock()
defer c.statusMu.RUnlock()
return c.status
}
func (c *Client) setErr(msg string) {
c.statusMu.Lock()
was := c.status.LastError
c.status.Connected = false
c.status.LastError = msg
c.statusMu.Unlock()
// Logged on CHANGE only: a disconnected amplifier is polled four times a
// second, and the log is where a hardware problem is diagnosed hours later.
if msg != "" && msg != was {
applog.Printf("kpa: %s", msg)
}
}
// dropLocked closes the connection. Caller holds c.mu.
func (c *Client) dropLocked() {
if c.conn != nil {
_ = c.conn.Close()
c.conn = nil
c.rd = nil
}
}
// connectLocked opens the transport. Caller holds c.mu.
func (c *Client) connectLocked() error {
if c.conn != nil {
return nil
}
switch strings.ToLower(strings.TrimSpace(c.cfg.Transport)) {
case "tcp":
if strings.TrimSpace(c.cfg.Host) == "" {
return fmt.Errorf("no address configured for the amplifier")
}
addr := net.JoinHostPort(c.cfg.Host, fmt.Sprint(c.cfg.Port))
conn, err := net.DialTimeout("tcp", addr, dialTimeout)
if err != nil {
// Named for what it usually is. The KPA1500 accepts ONE TCP client,
// so the common failure is not a wrong address but the Elecraft
// utility already holding the socket — and "connection refused"
// sends an operator looking at their network instead.
return fmt.Errorf("cannot reach the amplifier on %s: %w (it accepts a single TCP connection — close the Elecraft utility or any other program using it)", addr, err)
}
c.conn = conn
default:
if strings.TrimSpace(c.cfg.ComPort) == "" {
return fmt.Errorf("no serial port configured for the amplifier")
}
p, err := serial.Open(c.cfg.ComPort, &serial.Mode{BaudRate: c.cfg.Baud})
if err != nil {
return fmt.Errorf("cannot open %s: %w", c.cfg.ComPort, err)
}
_ = p.SetReadTimeout(ioTimeout)
c.conn = p
}
c.rd = bufio.NewReader(c.conn)
applog.Printf("kpa: connected to the %s", c.status.Model)
return nil
}
// ask sends one command and reads its answer.
//
// The whole exchange is under the lock: with no flow control, two questions in
// flight means two answers to sort out, and the only thing distinguishing them
// is the prefix — which is exactly what payload() has to reject when it
// happens.
func (c *Client) ask(cmd string) (string, error) {
c.mu.Lock()
defer c.mu.Unlock()
if err := c.connectLocked(); err != nil {
return "", err
}
if tc, ok := c.conn.(net.Conn); ok {
_ = tc.SetDeadline(time.Now().Add(ioTimeout))
}
if _, err := c.conn.Write([]byte(cmd)); err != nil {
c.dropLocked()
return "", fmt.Errorf("writing %s: %w", cmd, err)
}
// Answers end with a semicolon and nothing else does, so the terminator is
// the frame.
line, err := c.rd.ReadString(';')
if err != nil {
c.dropLocked()
return "", fmt.Errorf("no answer to %s: %w", cmd, err)
}
return strings.TrimSpace(line), nil
}
// send is a SET: written, and not answered. The reference says SET commands do
// not generally produce a response, so waiting for one would stall the poll
// loop for a whole timeout every time the operator pressed a button.
func (c *Client) send(cmd string) error {
c.mu.Lock()
defer c.mu.Unlock()
if err := c.connectLocked(); err != nil {
return err
}
if tc, ok := c.conn.(net.Conn); ok {
_ = tc.SetDeadline(time.Now().Add(ioTimeout))
}
if _, err := c.conn.Write([]byte(cmd)); err != nil {
c.dropLocked()
return fmt.Errorf("writing %s: %w", cmd, err)
}
applog.Printf("kpa: → %s", cmd)
return nil
}
// Operate puts the amplifier in OPERATE (true) or STANDBY (false).
//
// Worth knowing, and worth saying in the UI: from firmware 01.41 onwards,
// going to OPERATE also CLEARS the current fault — every one except
// temperature, which clears by cooling. So this button is the way out of a
// fault as well as the way into transmit.
func (c *Client) Operate(on bool) error {
if on {
return c.send("^OS1;")
}
return c.send("^OS0;")
}
// ClearFault clears the current fault without changing mode (^FLC).
func (c *Client) ClearFault() error { return c.send("^FLC;") }
// PowerOn switches the main supplies on or off (^ON1 / ^ON0).
//
// Off is a real power-down, not standby, and the way back on over the network
// is Wake-on-LAN or the front panel — so a caller should be asking the operator
// first. The sleeping microcontroller does answer ^ON while the supplies are
// off, which is why "off" is a state this can report rather than a silence.
func (c *Client) PowerOn(on bool) error {
if on {
return c.send("^ON1;")
}
return c.send("^ON0;")
}
// Tune starts an ATU tune cycle (^FT). It needs drive from the transceiver.
func (c *Client) Tune() error { return c.send("^FT;") }
// pollLoop keeps the status fresh, reconnecting as needed.
func (c *Client) pollLoop() {
t := time.NewTicker(pollInterval)
defer t.Stop()
var n uint64
for {
select {
case <-c.stop:
return
case <-t.C:
c.pollOnce(n)
n++
}
}
}
func (c *Client) pollOnce(n uint64) {
// Forward power and SWR in ONE exchange (^WS), which is why that command
// exists and why the two are not asked separately.
reply, err := c.ask("^WS;")
if err != nil {
c.setErr(err.Error())
return
}
w, swr, err := parseWS(reply)
if err != nil {
c.setErr(err.Error())
return
}
c.statusMu.Lock()
c.status.Connected = true
c.status.LastError = ""
c.status.FwdW, c.status.SWR = w, swr
c.statusMu.Unlock()
// The fault, every cycle: it puts the amplifier in standby by itself, and an
// operator watching a power bar needs to know why it stopped moving.
if reply, err := c.ask("^FL;"); err == nil {
if code, err := parseFault(reply); err == nil {
c.statusMu.Lock()
was := c.status.FaultCode
c.status.FaultCode = code
c.status.FaultText = FaultName(code)
c.statusMu.Unlock()
if code != was && code != 0 {
applog.Printf("kpa: FAULT %02X — %s", code, FaultName(code))
}
}
}
if n%slowEvery != 0 {
return
}
// The readings that do not move fast. Each is optional: an older firmware or
// a KPA500 that does not know one of these must not take the rest down with
// it, so a failure here leaves the previous value standing.
if reply, err := c.ask("^OS;"); err == nil {
if v, err := parseInt(reply, "^OS"); err == nil {
c.statusMu.Lock()
c.status.Operate = v == 1
c.statusMu.Unlock()
}
}
if reply, err := c.ask("^ON;"); err == nil {
if v, err := parseInt(reply, "^ON"); err == nil {
c.statusMu.Lock()
c.status.PowerOn = v == 1
c.statusMu.Unlock()
}
}
if reply, err := c.ask("^VI;"); err == nil {
if v, a, err := parseVI(reply); err == nil {
c.statusMu.Lock()
c.status.VoltV, c.status.CurA = v, a
c.statusMu.Unlock()
}
}
if reply, err := c.ask("^TM;"); err == nil {
if v, err := parseInt(reply, "^TM"); err == nil {
c.statusMu.Lock()
c.status.TempC = v
c.statusMu.Unlock()
}
}
if reply, err := c.ask("^BN;"); err == nil {
if v, err := parseInt(reply, "^BN"); err == nil {
c.statusMu.Lock()
c.status.Band = BandName(v)
c.statusMu.Unlock()
}
}
if reply, err := c.ask("^TP;"); err == nil {
if v, err := parseInt(reply, "^TP"); err == nil {
c.statusMu.Lock()
c.status.Tuning = v == 1
c.statusMu.Unlock()
}
}
}