Interfacing to cc1101 using c style interrupt driven trampoline functions

To connect a raw radio transceiver like the CC1101 to the Pico-IoT-Replacement OS, utilizing trampoline interrupts is the most robust design choice.

In embedded C++, class member functions carry a hidden this pointer argument. Because of this, the hardware Interrupt Service Routine (ISR) cannot jump directly to a class method. A trampoline interrupt is a sleek, static C-style function that serves as the bridge. It intercepts the raw hardware wire trigger from the CC1101, instantly binds the execution back into the concrete object context, and manipulates the memory ring buffers.

By locking this entire architecture onto Core 1, we bypass all Web Server/mDNS task interference entirely.

1. High-Speed CC1101 Interrupt Mechanics

The CC1101 module features two digital output status lines: GDO0 and GDO2. You configure the CC1101's internal registers (IOCFG0 / IOCFG2) to fire these pins when specific RF lifecycle thresholds are met: [1, 2]

• In RX Mode: The pin goes HIGH when a valid packet sync word is discovered in the air, and drops LOW when the complete packet packet structure finishes landing in the CC1101's internal 64-byte FIFO buffer.
• In TX Mode: The pin goes HIGH when the internal FIFO buffer fills up, and drops LOW once the transmission cycle completes. [1]

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2. The Trampoline Architecture Blueprint (C++)

This production-grade wrapper shows how to tie structural memory ring buffers directly into the RP2040’s native SDK hardware interrupt layer (hardware/gpio.h).

cpp

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"
#include "hardware/spi.h"

#define BUFFER_SIZE 512
#define CC1101_GDO0_PIN 22 // Adjust to your physical wiring map

class CC1101Transceiver {
private:
    // Core memory buffers for real-time streaming
    uint8_t rx_ring_buffer[BUFFER_SIZE];
    uint8_t tx_ring_buffer[BUFFER_SIZE];
    
    volatile uint32_t rx_head = 0;
    volatile uint32_t rx_tail = 0;
    
    // SPI Hardware reference
    spi_inst_t* spi_port;
    uint32_t csn_pin;

    // Isolate SPI transactions within the ISR context
    uint8_t readRegDirect(uint8_t addr) {
        uint8_t val;
        gpio_put(csn_pin, 0);
        spi_write_blocking(spi_port, &addr, 1);
        spi_read_blocking(spi_port, 0, &val, 1);
        gpio_put(csn_pin, 1);
        return val;
    }

public:
    CC1101Transceiver(spi_inst_t* spi, uint32_t csn) : spi_port(spi), csn_pin(csn) {}

    // 1. The Concrete Instance ISR Handler Method
    void handle_hardware_trigger() {
        // Query the CC1101 FIFO status register (0x3B = RXBYTES status)
        uint8_t rx_bytes_waiting = readRegDirect(0x3B) & 0x7F;

        if (rx_bytes_waiting > 0) {
            gpio_put(csn_pin, 0);
            uint8_t fifo_addr = 0x3F | 0xC0; // 0x3F FIFO address + Burst Read flags
            spi_write_blocking(spi_port, &fifo_addr, 1);

            for (int i = 0; i < rx_bytes_waiting; ++i) {
                uint8_t incoming_byte;
                spi_read_blocking(spi_port, 0, &incoming_byte, 1);
                
                // Slam byte into ring memory buffer
                uint32_t next_head = (rx_head + 1) % BUFFER_SIZE;
                if (next_head != rx_tail) { // Avoid buffer wrapping overflows
                    rx_ring_buffer[rx_head] = incoming_byte;
                    rx_head = next_head;
                }
            }
            gpio_put(csn_pin, 1);
        }
    }

    // Read utility method for Core 1 Task scheduler loops
    bool pop_rx_byte(uint8_t* out_byte) {
        if (rx_head == rx_tail) return false; // Buffer empty
        *out_byte = rx_ring_buffer[rx_tail];
        rx_tail = (rx_tail + 1) % BUFFER_SIZE;
        return true;
    }
};

// ============================================================================
// THE TRAMPOLINE BRIDGE LAYER
// ============================================================================
// Standard C-linkage static pointers to hold object context for the raw vector table
static CC1101Transceiver* global_cc1101_instance = nullptr;

// The actual naked static Trampoline Function pointed to by the RP2040 vector map
void static_cc1101_trampoline_isr(uint gpio, uint32_t events) {
    // If the global context bridge is initialized, pivot execution instantly
    if (global_cc1101_instance != nullptr) {
        global_cc1101_instance->handle_hardware_trigger();
    }
}

3. Registering the Driver Into Your Core 1 Core Boot Loop

During your firmware's hardware instantiation setup sequence, assign your concrete object context to the trampoline hook right before enabling the global interrupt lines:

cpp

void init_tricorder_rf_subsystem() {
    // 1. Instantiate the Transceiver object layout 
    static CC1101Transceiver cc1101(spi0, 17); // Using SPI0, CSN Pin 17
    
    // 2. Hydrate the static context bridge pointer
    global_cc1101_instance = &cc1101;

    // 3. Bind the raw GDO0 pin to the static Trampoline function
    gpio_init(CC1101_GDO0_PIN);
    gpio_set_dir(CC1101_GDO0_PIN, GPIO_IN);
    
    // Wire the callback vector to our static trampoline function
    gpio_set_irq_enabled_with_callback(
        CC1101_GDO0_PIN, 
        GPIO_IRQ_EDGE_FALL, // Fires when GDO0 transitions from High to Low (Packet Complete)
        true, 
        &static_cc1101_trampoline_isr
    );
}

4. Hooking the Memory Buffers into your Registry Tasks

Because the trampoline handler slides packet data directly into rx_ring_buffer completely in the background, your main scheduler task on Core 1 can poll for fresh packets safely and fluidly:

cpp

// This cooperative task loops continuously inside Core 1's execution ring
void cc1101_scheduler_processing_task() {
    uint8_t raw_packet_accumulator[64];
    int packet_index = 0;
    uint8_t active_byte;

    // Pull any byte streams extracted by the trampoline interrupt
    while (global_cc1101_instance->pop_rx_byte(&active_byte)) {
        raw_packet_accumulator[packet_index++] = active_byte;
        if (packet_index >= 64) break; // Truncate at maximum packet limit
    }

    if (packet_index > 0) {
        // Stringify the payload into a clean hexadecimal string
        char hex_output_buffer[128] = {0};
        for(int i = 0; i < packet_index; i++) {
            sprintf(&hex_output_buffer[i*2], "%02X", raw_packet_accumulator[i]);
        }
        
        // Push the result to your Core 0 Central Registry thread-safely
        setRegistryValue("rf_sniff", hex_output_buffer);
    }
}

Architectural Advantages for your C AI Core

By organizing data via this trampoline structure, your Embedded C Neural Network framework can pull raw bytes out of these exact ring buffers without locking up the CPU. If we configure the CC1101 to capture raw amplitude metrics (RSSI), we can stream those values straight into a 784-element array and call your forward_pass() to classify background radio noise patterns concurrently alongside the radiation sensor processing loops!