System Overview & Architecture

The Aslandi Edge Converter (planovi-converter) is a high-reliability industrial IoT edge gateway built for energy management and cooperative balancing in the Planovi ecosystem. Built on the Raspberry Pi Pico 2 W (featuring the dual-core RP2350 microcontroller), the gateway autonomously interrogates RS-485 Modbus energy meters, buffers timestamped telemetry in power-loss-resilient offline queues, and transmits authenticated data to the Planovi cloud via mTLS and MQTT QoS 1.

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1. High-Level System Topology

The gateway operates at the boundary between industrial facility electrical switchboards and the Planovi cloud platform:

flowchart TB
    subgraph Meters["⚡ Substation & Building Energy Meters"]
        M1["Zamel LEM-60 (Single Phase)"]
        M2["CHINT DTSU666 (Three Phase)"]
        Mn["Up to 50 Modbus RTU Meters (Bus Channel 0)"]
        M1 --- Mn
        M2 --- Mn
    end

    subgraph Hardware["🎛️ Aslandi Edge Converter (RP2350 Hardware Stack)"]
        RS485["Waveshare Pico-2CH-RS485 Transceiver"]
        RP2350["Raspberry Pi Pico 2 W (RP2350 @ 150MHz)
• FreeRTOS 11.1 Multitasking Kernel
• lwIP TCP/IP Stack & MbedTLS"]
        RTC["PCF8523 / DS3231 RTC + CR1220 Battery"]
        SD["MicroSD Storage (Authenticated Generations)"]
        WiFi["CYW43439 Wi-Fi (SoftAP & Station Mode)"]
        
        RS485 --- RP2350
        RTC --- RP2350
        SD --- RP2350
        WiFi --- RP2350
    end

    subgraph Ingress["🌐 Cloud & Management Ingress"]
        Installer["Installer Laptop / Smartphone
(Local HTTP Panel: 192.168.4.1)"]
        MQTTBroker["Secure MQTT Broker (mTLS Port 8883)"]
        FastAPI["Planovi Backend Gateway
(FastAPI / Supabase Edge Functions)"]
        DB[("PostgreSQL Telemetry Ledger")]
    end

    Mn -->|"Modbus RTU (9600 8N1)"| RS485
    WiFi -.->|"Commissioning SoftAP"| Installer
    RP2350 -->|"MQTT QoS 1 / mTLS"| MQTTBroker
    MQTTBroker --> FastAPI
    FastAPI --> DB

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2. Hardware Stack & Microcontroller Baseline

Component	Specification	Function
Microcontroller	Raspberry Pi RP2350 (Dual ARM Cortex-M33 @ 150 MHz)	Core compute, cryptographic acceleration, FreeRTOS tasks.
Volatile Memory	520 KiB on-chip SRAM	Task stacks, LittleFS buffers, mTLS handshake buffers.
Non-Volatile Flash	4 MiB QSPI Flash	Dual-slot A/B firmware images, redundant configs, LittleFS FIFO.
Wireless Transceiver	Infineon CYW43439 (802.11 b/g/n)	Station mode (cloud uplink) and SoftAP (installer setup).
RS-485 Transceiver	Waveshare Pico-2CH-RS485 (Galvanic isolation)	Differential RS-485 communications on Channel 0.
Real-Time Clock	PCF8523 / DS3231 (I2C) with CR1220 coin cell	Sub-second timestamping independent of network connectivity.
Removable Storage	MicroSD Card (SPI interface, up to 32 GB)	Encrypted long-term telemetry archive with dual-mirror blocks.

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3. 4 MiB Flash Memory Layout

The internal 4 MiB QSPI Flash memory is partitioned into dedicated regions ensuring safe updates, fault containment, and transactional configuration:

Region	Offset	Size	Purpose
Bootloader	0x000000	64 KiB	ECDSA P-256 image verification, slot selection, rollback logic.
Slot A (Active/Candidate)	0x010000	1,920 KiB	Primary signed firmware executable image.
Slot B (Passive/Rollback)	0x1F0000	1,920 KiB	Secondary signed firmware executable image.
Configuration Slot 1	0x3D0000	64 KiB	Redundant encrypted device configuration bank 1 (CRC32/HMAC).
Configuration Slot 2	0x3E0000	64 KiB	Redundant encrypted device configuration bank 2 (CRC32/HMAC).
LittleFS Telemetry Buffer	0x3F0000	64 KiB	Wear-leveled circular FIFO queue holding ~205,000 records.

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4. FreeRTOS Multitasking Task Architecture

The firmware runs FreeRTOS 11.1 with prioritized cooperative tasks:

graph TD
    subgraph Core0["RP2350 Core 0"]
        T1["Modbus Task
(Periodic register polling, 9600 8N1)"]
        T2["Storage Task
(LittleFS FIFO writes & SD card block sync)"]
        T3["Diagnostics Task
(Watchdog feeding, RTC sync, temperature)"]
    end

    subgraph Core1["RP2350 Core 1"]
        T4["Networking & HTTP Task
(CYW43 Wi-Fi, lwIP stack, Web Server)"]
        T5["Cloud Uplink Task
(mTLS session, MQTT QoS 1 publishing)"]
    end

    Queue1[("In-Memory FreeRTOS Telemetry Queue")]

    T1 -->|Raw Readings| Queue1
    Queue1 -->|Persist| T2
    Queue1 -->|Publish| T5
    T4 -.->|Configuration Changes| T2

1. Modbus Polling Task: Sequentially queries registered meters on Channel 0 using configured Modbus register profiles.
2. Storage Task: Serializes readings into telemetry schema v3 and enqueues records into the LittleFS flash queue and mirrored microSD blocks.
3. Cloud Uplink Task: Maintains an mTLS connection with the MQTT broker, publishing buffered records with QoS 1 and popping them from the FIFO only after broker ACK (PUBACK).
4. Networking & HTTP Task: Runs the lwIP web server providing the installer web interface for Wi-Fi provisioning, meter configuration, and status diagnostics.
5. Diagnostics Task: Monitors system invariants, resets the hardware watchdog timer (8 seconds timeout), checks RTC battery health, and logs diagnostic alarm counters.