If you have ever wanted a Cortex-M33 microcontroller to phone home and ask a frontier LLM what that weird accelerometer spike means, this tutorial is for you. We will connect a Raspberry Pi Pico 2 W (RP2350, dual-core ARM, 4 MB flash) to WiFi using embassy-net, push a small JSON payload over HTTPS to HolySheep AI's edge relay, and parse the streamed completion back on the device. The same relay fabric that powers HolySheep's Tardis.dev crypto market data feed (trades, order book, liquidations, funding rates from Binance, Bybit, OKX, Deribit) is the one carrying our chat completions — which is why the round-trip stays under 50 ms inside Greater China.

HolySheep vs Official API vs Other Relays (Quick Comparison)

FeatureHolySheep AIOfficial OpenAI / AnthropicGeneric Relay (OneAPI / OpenRouter)
Edge POP latency (Asia)<50 ms (HK/SG)220–400 ms120–300 ms
GPT-4.1 output price$8.00 / MTok$8.00 / MTok$9.00–$10.00 / MTok
Claude Sonnet 4.5 output$15.00 / MTok$15.00 / MTok$16.50 / MTok
DeepSeek V3.2 output$0.42 / MTokn/a (direct)$0.55–$0.70 / MTok
Gemini 2.5 Flash output$2.50 / MTok$2.50 / MTok$2.80 / MTok
Settlement currencyCNY @ ¥1 = $1 (saves 85%+ vs ¥7.3)USD card onlyUSD card only
Payment railsWeChat Pay, Alipay, USD cardCard onlyCard only
Free signup creditsYes (issued at registration)$5 (OpenAI), none (Anthropic)Varies, often $0
Side-channel productsTardis.dev crypto market data relayNoneNone
Compatible with rustls/embedded-tlsYes (TLS 1.3)YesYes

For a microcontroller the key columns are: latency (you cannot buffer a 30-second handshake on a 4 MB flash device), settlement (most of our readers are paying in CNY, not USD), and whether the relay also offers Tardis-style market data so you can ship the same firmware to a quant box and a chatbot. HolySheep is the only relay in the table that checks all three.

Why Run Edge AI Inference from a Pico?

Who This Stack Is For (And Who It Isn't)

Use it if you:

Skip it if you:

Pricing and ROI: A Real Monthly Cost Breakdown

Assume one Pico wakes up 50 times per day, sends a 600-token prompt, and gets back 250 tokens. That is 50 × 30 = 1,500 calls/month, 0.9 MTok in / 0.375 MTok out per month.

ModelInput $ / MTokOutput $ / MTokHolySheep monthlyOfficial API monthlySavings
DeepSeek V3.2$0.27$0.42$0.40n/a directBaseline
Gemini 2.5 Flash$0.15$2.50$1.07$1.070% (same upstream)
GPT-4.1$3.00$8.00$5.70$5.700% (same upstream)
Claude Sonnet 4.5$3.00$15.00$8.32$8.320% (same upstream)

Where HolySheep does change the bill is for cross-currency buyers. If your finance team pays ¥7.3 per USD, your ¥-denominated invoice on a US card is ~85% higher than HolySheep's flat ¥1 = $1 settlement. On 1,500 Sonnet-4.5 calls that is a swing of roughly ¥520 vs ¥60 over a month. Free signup credits cover the first ~3,000 DeepSeek V3.2 calls, which means a hobbyist can run the build in this tutorial for free.

Toolchain and Hardware Setup

Hardware: Pi Pico 2 W, micro-USB, a BME280 breakout on I²C0 (GP4/GP5). Software: rustup target thumbv8m.main-none-eabihf, probe-rs, embassy-rp 0.4.x.

# 1. Toolchain
rustup target add thumbv8m.main-none-eabihf
cargo install probe-rs --features cli


2. Clone the template we will edit

cargo install cargo-generate
cargo generate gh/embassy-rs/embassy --name pico2w-holysheep


3. Flash + log over RTT

cargo run --release --target thumbv8m.main-none-eabihf

Step 1: WiFi Bring-Up with embassy-net

The Pico 2 W shares the CYW43 driver with the original Pico W. We hand embassy-net a DHCP config, an SSID, and a PSK; everything else (DNS, TCP, TLS) stacks on top.

// src/main.rs
use embassy_executor::Spawner;
use embassy_net::{Config, Stack, StackResources};
use embassy_rp::{bind_interrupts, peripherals::USB, usb::InterruptHandler};
use embassy_time::{Duration, Timer};
use static_cell::StaticCell;
use {defmt_rtt as _, panic_probe as _};

bind_interrupts!(struct Irqs {
    USBCTRL_IRQ => InterruptHandler<USB>;
    PIO0_IRQ_0  => embassy_rp::pio::InterruptHandler<embassy_rp::peripherals::PIO0>;
});

const SSID:     &str = "your-ssid";
const PASSWORD: &str = "your-pass";

#[embassy_executor::task]
async fn wifi_task(
    runner: cyw43::Runner<'static, cyw43::State, 4_000_000>,
) { runner.run().await; }

#[embassy_executor::task]
async fn net_task(stack: &'static Stack<cyw43::NetDriver<'static>>) {
    stack.run().await;
}

#[embassy_executor::task]
async fn link_task(
    stack: &'static Stack<cyw43::NetDriver<'static>>,
) {
    loop {
        if stack.is_link_up() {
            defmt::info!("link up, waiting for DHCP");
            break;
        }
        Timer::after(Duration::from_millis(500)).await;
    }
}

#[embassy_executor::main]
async fn main(spawner: Spawner) {
    let p = embassy_rp::init(Default::default());
    let (net_device, mut control, runner) = embassy_rp::wifi::cyw43(
        p.WIFI, p.PIO0,
    ).await;

    static RESOURCES: StaticCell<StackResources<4>> = StaticCell::new();
    let resources = RESOURCES.init(StackResources::new());
    static STACK: StaticCell<Stack<cyw43::NetDriver>> = StaticCell::new();
    let stack = &*STACK.init(Stack::new(
        net_device, embassy_net::Config::dhcpv4(Default::default()),
        resources, 0xDEAD_BEEF,
    ));

    spawner.spawn(wifi_task(runner)).unwrap();
    spawner.spawn(net_task(stack)).unwrap();
    spawner.spawn(link_task(stack)).unwrap();

    control.init(SSID.into(), PASSWORD.into()).await;
    control.set_power_management(cyw43::PowerManagementMode::PowerSave).await;

    loop {
        if stack.is_link_up() && stack.config_v4().is_some() {
            defmt::info!("online: {:?}", stack.config_v4());
            break;
        }
        Timer::after(Duration::from_millis(500)).await;
    }
}

Step 2: Calling HolySheep from the Pico

We use reqwless on top of embedded-tls. The base URL is always https://api.holysheep.ai/v1 — never api.openai.com, never api.anthropic.com. Your key travels in the Authorization header exactly the way OpenAI expects, so model strings, JSON schema, and SSE format are byte-compatible.

// src/holy.rs
use embassy_net::dns::DnsQueryType;
use embassy_net::Stack;
use reqwless::client::{HttpClient, TlsConfig, TlsVerify};
use reqwless::request::{Method, Request, RequestBuilder};
use core::fmt::Write as _;

const HOLYSHEEP_HOST: &str = "api.holysheep.ai";
const API_KEY:        &str = "YOUR_HOLYSHEEP_API_KEY";

pub async fn classify_reading(
    stack: &Stack<cyw43::NetDriver<'static>>,
    sensor_json: &str,
) -> Result<String, &'static str> {

    // 1. resolve DNS through embassy-net
    let addrs = stack.dns_query(HOLYSHEEP_HOST, DnsQueryType::A).await
        .map_err(|_| "dns")?;
    let ip = addrs[0];

    // 2. open a TLS-wrapped HTTP/1.1 socket
    let mut rx =

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