sh2sc-edt/transmitter_8h_source.html

#pragma once


#include <Arduino.h>

#include "protocol.h"

#include "csprng.h"

#include <ChaChaPoly.h>


const uint8_t  TX_BUTTON_PIN        = 3;

const uint8_t  ENTROPY_RING_OSC_PIN = 2;

const uint8_t  TX_LCD_ADDR          = 0x3E;

const uint8_t  TX_LCD_COLS          = 16;

const uint8_t  TX_LCD_ROWS          = 2;

 // end group tx_hw_pins

const uint16_t DEBOUNCE_DELAY_MS     = 50;

const uint32_t RECONNECT_INTERVAL_MS = 2000;

 // end group tx_timing


enum class TxState : uint8_t {

  IDLE,

  RECONNECTING,

  SENDING_HELLO,

  WAITING_HELLO_ACK,

  SENDING,

  WAITING_ACK,

  WAIT_BETWEEN_NOTES,

  SENDING_FIN,

  WAITING_FIN_ACK

};


void tx_setup();


void tx_loop();


void suspendSession();


bool readButtonPress();


void sendHelloPacket();


void sendPacket(uint8_t noteIndex, uint16_t noteDurationMs, uint8_t seqNum);


void formAndSendPacket(uint8_t note_idx, uint16_t duration_ms);


void sendFinPacket();


void updateTxDisplay(TxState state, uint16_t seqNum, uint8_t retries);


void generateEntropyPool(uint8_t* outputSeed);

csprng.h
ChaCha20-based CSPRNG for SH2SC-EDT — Transmitter Node A (ATmega328P).

protocol.h
Shared C2P-ARQ protocol definitions for SH2SC-EDT (Transmitter Node A).

seqNum
static uint16_t seqNum
Packet sequence number (0–65535, wraps).
Definition TransmitterNode.ino:30

TX_BUTTON_PIN
const uint8_t TX_BUTTON_PIN
Tactile start button (INPUT_PULLUP, active LOW).
Definition transmitter.h:22

TX_LCD_COLS
const uint8_t TX_LCD_COLS
Number of columns on the TX LCD.
Definition transmitter.h:25

ENTROPY_RING_OSC_PIN
const uint8_t ENTROPY_RING_OSC_PIN
Hardware ring oscillator entropy source (INT0).
Definition transmitter.h:23

TX_LCD_ROWS
const uint8_t TX_LCD_ROWS
Number of rows on the TX LCD.
Definition transmitter.h:26

TX_LCD_ADDR
const uint8_t TX_LCD_ADDR
I2C address of the Aip31068 16x2 LCD display.
Definition transmitter.h:24

DEBOUNCE_DELAY_MS
const uint16_t DEBOUNCE_DELAY_MS
Definition transmitter.h:33

RECONNECT_INTERVAL_MS
const uint32_t RECONNECT_INTERVAL_MS
Auto-reconnect HelloPacket broadcast interval (ms) while in RECONNECTING state.
Definition transmitter.h:35

suspendSession
void suspendSession()
Suspend the current C2P-ARQ session and enter the Self-Healing reconnect loop.
Definition TransmitterNode.ino:426

updateTxDisplay
void updateTxDisplay(TxState state, uint16_t seqNum, uint8_t retries)
Refresh the TX LCD with the current ARQ status and FSM state label.
Definition TransmitterNode.ino:228

sendHelloPacket
void sendHelloPacket()
Generate a fresh 12-byte CSPRNG session nonce and transmit it as a HelloPacket.
Definition TransmitterNode.ino:118

sendFinPacket
void sendFinPacket()
Construct and transmit the FLAG_FIN session-close packet.
Definition TransmitterNode.ino:266

TxState
TxState
Finite State Machine states for the C2P-ARQ Transmitter (Node A).
Definition transmitter.h:72

TxState::SENDING_FIN
@ SENDING_FIN
All notes delivered; transmitting the FLAG_FIN teardown packet.

TxState::WAITING_ACK
@ WAITING_ACK
DataPacket sent; listening on the feedback line for ACK or NACK.

TxState::SENDING_HELLO
@ SENDING_HELLO
Generating a CSPRNG nonce and transmitting the SYN handshake packet.

TxState::IDLE
@ IDLE
Waiting for a button press to begin melody playback.

TxState::SENDING
@ SENDING
Constructing, encrypting, and transmitting the current DataPacket.

TxState::WAITING_HELLO_ACK
@ WAITING_HELLO_ACK
HelloPacket sent; awaiting RX nonce-acceptance ACK.

TxState::WAIT_BETWEEN_NOTES
@ WAIT_BETWEEN_NOTES
ACK received; holding the inter-note gap before advancing melodyIndex.

TxState::RECONNECTING
@ RECONNECTING
Link lost mid-melody; broadcasting HelloPackets every RECONNECT_INTERVAL_MS.

TxState::WAITING_FIN_ACK
@ WAITING_FIN_ACK
FIN packet sent; awaiting RX acknowledgement before erasing the session nonce.

generateEntropyPool
void generateEntropyPool(uint8_t *outputSeed)
Harvest 256 bits of hardware entropy and write them to outputSeed.
Definition TransmitterNode.ino:345

tx_loop
void tx_loop()
Execute one non-blocking FSM tick for the Transmitter node.
Definition TransmitterNode.ino:486

tx_setup
void tx_setup()
Initialise TX hardware: UART, I2C LCD, button pin, ring-oscillator entropy.
Definition TransmitterNode.ino:454

readButtonPress
bool readButtonPress()
Read and debounce the start button using a millis()-based filter.
Definition TransmitterNode.ino:71

formAndSendPacket
void formAndSendPacket(uint8_t note_idx, uint16_t duration_ms)
High-level wrapper called by the SENDING FSM state.
Definition TransmitterNode.ino:209

sendPacket
void sendPacket(uint8_t noteIndex, uint16_t noteDurationMs, uint8_t seqNum)
Encrypt and transmit a single DataPacket for the given note.