UART layer

The UART module implements a binary frame protocol for bidirectional communication between ESP32 (Link) and RP2040 (Controller). Used in dual-MCU devices: iDryer LINK, iHeater LINK.

Storage Link does not use the UART module — it is a standalone ESP32-C3 device without a second MCU.

Include separately:

#include <idryer_uart.h>

Physical layer

• UART 8N1, 115200 baud (default), no hardware flow control.
• Maximum frame payload: 200 bytes.
• CRC-16/CCITT (poly 0x1021, init 0xFFFF) per frame.

Frame structure

byte 0  : SOF = 0xAA
byte 1  : version = 1
byte 2  : flags   (ACK required | is ACK | error | fragment | last fragment)
byte 3  : message kind (UartMsgKind)
byte 4  : sequence number (0..255, wrap)
byte 5  : payload length
payload : data (0..200 bytes)
crc16   : CRC, low byte + high byte

Classes

UartBridge

Main class of the module. Processes the incoming stream byte by byte, builds frames, verifies CRC, manages ACK/retry, and dispatches frames to registered callbacks.

UartBridge bridge;
bridge.begin(&Serial1, 115200);

// Register handlers before begin()
bridge.setHelloHandler([&](const UartHelloPayload& p, const UartFrameHeader&) {
    cloud.setMcuSerial(p.mcuSerial);
    UartHelloAckPayload ack{};
    bridge.sendHelloAck(ack);
});

// in loop():
bridge.loop();

Send methods are split into two groups:

• ESP32 → RP2040: sendHelloAck, sendCommand, sendProfileCommand, sendConfigPush, sendHeartbeat, sendClaimStatus, sendClaimComplete, sendWsStatus, sendTelemetryAck, sendCommandAck, sendConfigAck.
• RP2040 → ESP32 (or for tests): sendHello, sendTelemetry, sendStatus, sendWeights, sendRfid.

ACK/retry: frames with the UART_FLAG_ACK_REQ flag are retried up to 3 times with a 700 ms timeout. If no ACK is received — send* returns false.

Message types

Kind	Code	Direction	Purpose
Hello	0x01	RP2040 → ESP32	Announcement at startup; contains MCU serial, device type, capabilities
HelloAck	0x02	ESP32 → RP2040	Response with IP address and SSID
Telemetry	0x10	RP2040 → ESP32	Temperature, humidity, heater power
Weights	0x12	RP2040 → ESP32	Scale readings
Status	0x13	RP2040 → ESP32	Current drying mode, session progress
Rfid	0x14	RP2040 → ESP32	RFID event (tag detected/removed)
Command	0x20	ESP32 → RP2040	Command from backend (start, stop, find...)
ConfigPush	0x30	ESP32 → RP2040	Configuration (simple or chunked)
Heartbeat	0x40	ESP32 → RP2040	Uptime, RSSI, cloud state
Error	0x50	both	Protocol error
ClaimStart..Complete	0x70–0x72	both	Claiming lifecycle
WsEnable..StatusRequest	0x73–0x76	both	WebSocket server control on RP2040

ConfigReceiver / ConfigSender

Utility classes for transferring large JSON configs over UART in fragments (each fragment ≤ 194 bytes of data).

// Receive (ESP32 ← RP2040)
ConfigReceiver rx;
bridge.setConfigChunkHandler([&rx, &mqtt](const UartConfigChunkPayload& p, uint8_t len, const UartFrameHeader& hdr) {
    if (rx.processFragment(p, len, hdr.flags) == ConfigFragResult::Complete) {
        mqtt.publishConfigRaw(rx.getJson(), rx.getLength());
        rx.reset();
    }
});

// Send (ESP32 → RP2040)
ConfigSender tx;
uint16_t tid = ConfigSender::generateTransferId();
tx.send(json, length, tid, [&](const UartConfigChunkPayload& p, uint8_t payloadLen, uint8_t flags) {
    return bridge.sendConfigPushChunk(p, payloadLen, flags);
});

Integration with CloudStateMachine

Dual-MCU devices require the serial number from RP2040 before provisioning:

idryer::cloud::CloudConfig cfg;
cfg.waitForMcuSerial = true;
idryer::cloud::CloudStateMachine cloud(..., cfg);

bridge.setHelloHandler([&](const UartHelloPayload& p, const UartFrameHeader&) {
    cloud.setMcuSerial(p.mcuSerial);
    // ...
});

The state machine stays in WaitingForMcuSerial until setMcuSerial() is called.