hmc472/firmware/src/usb_serial.cpp

#include "usb_serial.h"

#include <Arduino.h>
#include <ArduinoJson.h>

#include "config.h"
#include "app.h"

static Attenuator* pAtten = nullptr;
static char rxBuf[USB_SERIAL_BUF_LEN];
static uint16_t rxLen = 0;
static bool overflow = false;
static bool wasConnected = false;  // Track USB CDC connection state

// --- Response helpers ---

static void sendOk(JsonDocument& doc) {
    doc["ok"] = true;
    String out;
    serializeJson(doc, out);
    Serial.println(out);
}

static void sendError(const char* msg) {
    JsonDocument doc;
    doc["ok"] = false;
    doc["error"] = msg;
    String out;
    serializeJson(doc, out);
    Serial.println(out);
}

// --- Build common status payload ---

static void buildStatus(JsonDocument& doc) {
    // Use getSnapshot() for consistent multi-field read across cores
    AttenuatorState state = pAtten->getSnapshot();
    doc["attenuation_db"] = state.db;
    doc["step"] = state.step;

    JsonArray bits = doc["bits"].to<JsonArray>();
    for (int i = 0; i < 6; i++) {
        bits.add(state.bits[i]);
    }

    doc["uptime_s"] = millis() / 1000;
    doc["version"] = FW_VERSION;

    JsonObject sweep = doc["sweep"].to<JsonObject>();
    sweep["running"] = isSweeping();
    sweep["direction"] = getSweepDirection() > 0 ? "up" : "down";
    sweep["dwell_ms"] = getSweepDwellMs();
}

// --- Command handlers ---

static void cmdIdentify() {
    JsonDocument doc;
    doc["device"] = "hmc472a-attenuator";
    doc["protocol"] = "usb-serial-json-v1";
    doc["version"] = FW_VERSION;

    JsonArray cmds = doc["commands"].to<JsonArray>();
    cmds.add("identify");
    cmds.add("status");
    cmds.add("config");
    cmds.add("set");
    cmds.add("sweep");
    cmds.add("sweep_stop");

    sendOk(doc);
}

static void cmdStatus() {
    JsonDocument doc;
    buildStatus(doc);
    sendOk(doc);
}

static void cmdConfig() {
    JsonDocument doc;
    doc["version"] = FW_VERSION;
    doc["hostname"] = FW_HOSTNAME;
    doc["db_min"] = DB_MIN;
    doc["db_max"] = DB_MAX;
    doc["db_step"] = DB_STEP;
    doc["step_min"] = STEP_MIN;
    doc["step_max"] = STEP_MAX;
    sendOk(doc);
}

static void cmdSet(JsonDocument& req) {
    // Auto-stop sweep on manual set (prevents silent overwrite)
    if (isSweeping()) {
        stopSweep();
    }

    if (req["db"].is<float>()) {
        float db = req["db"].as<float>();
        if (isnan(db) || isinf(db)) {
            sendError("db must be a finite number");
            return;
        }
        pAtten->setDB(db);
    } else if (req["step"].is<int>()) {
        int stepVal = req["step"].as<int>();
        if (stepVal < STEP_MIN || stepVal > STEP_MAX) {
            sendError("step must be 0-63");
            return;
        }
        pAtten->setStep(static_cast<uint8_t>(stepVal));
    } else if (req["bits"].is<JsonArray>()) {
        JsonArray arr = req["bits"].as<JsonArray>();
        if (arr.size() != 6) {
            sendError("bits array must have exactly 6 elements");
            return;
        }
        uint8_t bits[6];
        for (int i = 0; i < 6; i++) {
            if (!arr[i].is<int>()) {
                sendError("bits elements must be integers");
                return;
            }
            int val = arr[i].as<int>();
            if (val != 0 && val != 1) {
                sendError("bits elements must be 0 or 1");
                return;
            }
            bits[i] = val;
        }
        pAtten->setBits(bits);
    } else {
        sendError("set requires db, step, or bits field");
        return;
    }

    // Return status after set
    JsonDocument doc;
    buildStatus(doc);
    sendOk(doc);
}

static void cmdSweep(JsonDocument& req) {
    bool up = true;
    uint32_t dwellMs = SWEEP_DWELL_MS_DEFAULT;

    if (req["direction"].is<const char*>()) {
        up = strcmp(req["direction"].as<const char*>(), "down") != 0;
    }
    if (req["dwell_ms"].is<int>()) {
        int raw = req["dwell_ms"].as<int>();
        if (raw > 0) dwellMs = static_cast<uint32_t>(raw);
    }

    // Accept start/stop params for protocol compatibility, but current
    // sweep engine only supports full-range direction+dwell
    bool hasRangeParams = !req["start"].isNull() || !req["stop"].isNull();
    if (hasRangeParams && req["direction"].isNull()) {
        // Infer direction from start/stop
        float start = req["start"] | 0.0f;
        float stop = req["stop"] | 31.5f;
        up = (stop > start);
    }

    startSweep(up, dwellMs);

    JsonDocument doc;
    JsonObject sweep = doc["sweep"].to<JsonObject>();
    sweep["running"] = true;
    sweep["direction"] = up ? "up" : "down";
    sweep["dwell_ms"] = dwellMs;
    if (hasRangeParams) {
        doc["note"] = "start/stop range not yet supported; using full-range sweep with inferred direction";
    }
    sendOk(doc);
}

static void cmdSweepStop() {
    stopSweep();

    JsonDocument doc;
    JsonObject sweep = doc["sweep"].to<JsonObject>();
    sweep["running"] = false;
    sendOk(doc);
}

// --- Line dispatch ---

static void processLine(const char* line, uint16_t len) {
    JsonDocument req;
    DeserializationError err = deserializeJson(req, line, len);

    if (err) {
        sendError("invalid JSON");
        return;
    }

    if (!req["cmd"].is<const char*>()) {
        sendError("missing cmd field");
        return;
    }

    const char* cmd = req["cmd"].as<const char*>();

    if (strcmp(cmd, "identify") == 0) {
        cmdIdentify();
    } else if (strcmp(cmd, "status") == 0) {
        cmdStatus();
    } else if (strcmp(cmd, "config") == 0) {
        cmdConfig();
    } else if (strcmp(cmd, "set") == 0) {
        cmdSet(req);
    } else if (strcmp(cmd, "sweep") == 0) {
        cmdSweep(req);
    } else if (strcmp(cmd, "sweep_stop") == 0) {
        cmdSweepStop();
    } else {
        sendError("unknown command");
    }
}

// --- Public API ---

void setupUSBSerial(Attenuator& atten) {
    pAtten = &atten;
    Serial.begin(USB_SERIAL_BAUD);
    rxLen = 0;
    overflow = false;
    Serial0.println("[USBSerial] Initialized on native USB CDC");
}

void handleUSBSerial() {
    if (!pAtten) return;

    // Reset buffer on USB reconnect (prevents stale overflow state
    // from a disconnect mid-line corrupting the first command)
    bool connected = Serial;
    if (connected && !wasConnected) {
        rxLen = 0;
        overflow = false;
    }
    wasConnected = connected;

    while (Serial.available()) {
        char c = Serial.read();

        if (c == '\n' || c == '\r') {
            if (overflow) {
                // Line was too long — discard and report
                sendError("line too long (max 255 bytes)");
                overflow = false;
                rxLen = 0;
                return;  // One dispatch per loop iteration
            }
            if (rxLen > 0) {
                rxBuf[rxLen] = '\0';
                processLine(rxBuf, rxLen);
                rxLen = 0;
                return;  // One dispatch per loop iteration
            }
            // Empty line (bare \n or \r\n second byte) — ignore
            continue;
        }

        if (rxLen < USB_SERIAL_BUF_LEN - 1) {
            rxBuf[rxLen++] = c;
        } else {
            overflow = true;
        }
    }
}