Communication & Networking Modules

SyntropicOS provides a comprehensive suite of communication protocols ranging from zero-overhead byte stuffing and point-to-point packet routing up to industrial fieldbuses and automotive networks.

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Protocol Overview

Layer	Module	Header	Description
Framing	COBS	proto/syn_cobs.h	Consistent Overhead Byte Stuffing (0x00 packet delimiter)
Routing	Router	net/syn_router.h	Addressed packet dispatch (Node ID), type routing, & ACKs
Industrial	Modbus	proto/syn_modbus.h	Modbus RTU & Modbus TCP Master/Slave support
Metering	M-Bus	proto/syn_mbus.h	EN 13757-2 / EN 13757-3 European Meter Bus protocol
Automotive	ISO-TP	proto/syn_isotp.h	ISO 15765-2 multi-frame CAN transport layer
Automotive	J1939	proto/syn_j1939.h	SAE J1939 heavy vehicle network protocol (PGN / SPN)
Marine	NMEA 2000	proto/syn_n2k.h	NMEA 2000 marine CAN bus protocol decoder

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1. COBS & Packet Router Pipeline (syn_cobs + syn_router)

For MCU-to-MCU serial communication over UART TTL or RS232/RS485, SyntropicOS pairs COBS Framing with the Addressed Router.

Pipeline Data Flow

flowchart LR
    UART["Single-Byte UART RX Interrupt"] --> Decoder["syn_cobs_decoder_feed()"]
    Decoder -- 0x00 Delimiter Found --> Assembly["Decoded Frame"]
    Assembly --> Router["syn_router_feed()"]
    Router -- Match Node ID & Msg Type --> Callback["Handler Callback (e.g. on_set_led)"]

Complete STM32 HAL UART Single-Byte Interrupt Example

#include <syntropic/proto/syn_cobs.h>
#include <syntropic/net/syn_router.h>

#define MASTER_NODE_ID 0x01
#define SLAVE_NODE_ID  0x02
#define MSG_TYPE_LED   0x10

static uint8_t rx_byte;
static SYN_COBS_Decoder cobs_dec;
static uint8_t cobs_buf[128];

static SYN_Router router;
static SYN_RouterHandler handlers[4];

// Custom Transport: Send framed COBS packet over UART
static SYN_Status uart_send(const uint8_t *data, size_t len, void *ctx) {
    uint8_t enc[140];
    size_t enc_len = syn_cobs_encode(data, len, enc);
    enc[enc_len++] = 0x00; // Append 0x00 frame delimiter

    HAL_UART_Transmit(&huart2, enc, (uint16_t)enc_len, 100);
    return SYN_OK;
}

static SYN_Transport transport = { .send = uart_send, .ctx = NULL };

// COBS Decoder Callback when a complete frame arrives
static void on_cobs_frame(const uint8_t *data, size_t len, void *ctx) {
    syn_router_feed(&router, data, len);
}

// Single-Byte UART Interrupt Callback (No DMA)
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) {
    if (huart->Instance == USART2) {
        syn_cobs_decoder_feed(&cobs_dec, rx_byte);
        HAL_UART_Receive_IT(&huart2, &rx_byte, 1); // Re-arm interrupt
    }
}

// Message Handler Callback
static void on_led_command(const SYN_Packet *pkt, void *ctx) {
    if (pkt->len > 0 && pkt->payload[0] == 0x01) {
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_SET); // LED ON
    }
}

void app_init(void) {
    syn_cobs_decoder_init(&cobs_dec, cobs_buf, sizeof(cobs_buf), on_cobs_frame, NULL);

    syn_router_init(&router, SLAVE_NODE_ID, &transport, handlers, 4);
    syn_router_register(&router, MSG_TYPE_LED, on_led_command, NULL);

    HAL_UART_Receive_IT(&huart2, &rx_byte, 1);
}

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2. M-Bus Protocol (syn_mbus.h)

The M-Bus (Meter-Bus) driver supports utility metering devices (water, gas, electricity, heat meters) compliant with EN 13757-2 / EN 13757-3.

Features

• Single-byte ACK (0xE5) parsing.
• Short frame (0x10) and Long frame (0x68) header validation.
• Arithmetic checksum calculation and byte-at-a-time streaming parser.

#include <syntropic/proto/syn_mbus.h>

void parse_mbus_stream(const uint8_t *buffer, size_t len) {
    SYN_MBusFrame frame;
    if (syn_mbus_parse_long(buffer, len, &frame) == SYN_OK) {
        printf("M-Bus Frame Received! C-Field: 0x%02X, Address: 0x%02X\n",
               frame.control, frame.address);
    }
}