nRF-Modem

This is a library that provides a high-level async API for the modem on the Nordic nRF91* series chips (System-in-Packages). Supported chips are the following:

• nRF9160
• nRF9151
• nRF9161

It can be used with any executor.

Using

In your own program or library, you can depend on this crate in the usual fashion.

nrf9160:

[dependencies]
nrf-modem = { version = "x.x.x", features = ["nrf9160"] }

nrf9161:

[dependencies]
nrf-modem = { version = "x.x.x", features = ["nrf9161"] }

nrf9151:

[dependencies]
nrf-modem = { version = "x.x.x", features = ["nrf9151"] }

The built-in modem DNS resolver is blocking. If you want to use an async DNS resolver you can enable the feature dns-async. This will switch to an async implementation which uses publicly availabe DNS servers.

Errors and recovery

Dropping LteLink and Gnss (which also include all sockets and GnssStream) can lead to the modem staying active. There's an internal mutex that can be locked. Panicking is the only sane reaction to that. If you have a better idea, please open an issue or PR! The async deactivate function is way less likely to go wrong and you'll get a Result back so you know that something has gone wrong.

If anything does go wrong, has_runtime_state_error() will return true. Everything should stay working, but it's likely that the modem won't be properly turned off. This can be recovered by calling the reset_runtime_state() function when you've made sure nothing of the modem is used anymore.

Receiving packets with TLS

When receiving packets with TLS enabled, the nrf9160 modem can handle a maximum packet size of 2kB which is well below the default settings for most servers (see here). The library will throw an error with the variant TlsPacketTooBig if the modem receives a packet over this size. You will need to change settings at the server side if this error occurs, or use a proxy server.

Setup

There are a couple of things you must do to be able to use the library.

First of which, make sure to have the llvm-tools installed. This can be done using rustup component add llvm-tools-preview.

The library also needs some libc functions. The best way to import them is with tinyrlibc. As of writing the newest release is 0.3.0. This version does not include a needed API, so it's better to include the latest master branch or any newer released version.

This library has been tested with modem firmware version 1.3.4 but might work with earlier versions. When this library starts to require a newer version, then that will be seen as a breaking change. But it's easy to miss something, so this is a 'best effort' guarantee only.

Memory

The model library from Nordic needs some memory for its state and buffers. You need to reserve some memory in your memory.x file for the modem:

MEMORY
{
    FLASH : ORIGIN = 0x00000000, LENGTH = 1024K
    MODEM : ORIGIN = 0x20000000, LENGTH = 32K
    RAM   : ORIGIN = 0x20008000, LENGTH = 224K
}

Secure and nonsecure operation

The library can be used in secure and non-secure contexts. Some additional initialization is necessary for the secure context because the underlying libmodem C library by Nordic expects access to nonsecure memory and resources. If you do not use the memory layout defined above, you need to adapt the addresses below.

For running in the secure context:

// Initializing embassy_nrf has to come first because it assumes POWER and CLOCK at the secure address
let embassy_peripherals = embassy_nrf::init(Default::default());

// Set IPC RAM to nonsecure
const SPU_REGION_SIZE: u32 = 0x2000; // 8kb
const RAM_START: u32 = 0x2000_0000; // 256kb
let spu = embassy_nrf::pac::SPU;
let region_start = 0x2000_000 - RAM_START / SPU_REGION_SIZE;
let region_end = region_start + (0x2000_8000 - 0x2000_0000) / SPU_REGION_SIZE;
for i in region_start..region_end {
    spu.ramregion(i as usize).perm().write(|w| {
        w.set_execute(true);
        w.set_write(true);
        w.set_read(true);
        w.set_secattr(false);
        w.set_lock(false);
    })
}

// Set regulator access registers to nonsecure
spu.periphid(4).perm().write(|w| w.set_secattr(false));
// Set clock and power access registers to nonsecure
spu.periphid(5).perm().write(|w| w.set_secattr(false));
// Set IPC access register to nonsecure
spu.periphid(42).perm().write(|w| w.set_secattr(false));

Interrupts

The IPC interrupts must be routed to the modem software.

// Interrupt Handler for LTE related hardware. Defer straight to the library.
#[interrupt]
#[allow(non_snake_case)]
fn IPC() {
    nrf_modem::ipc_irq_handler();
}

let mut cp = unwrap!(cortex_m::Peripherals::take());

// Enable the modem interrupts
unsafe {
    NVIC::unmask(pac::Interrupt::IPC);
    cp.NVIC.set_priority(pac::Interrupt::IPC, 0 << 5);
}

Power

The DC/DC converter is automatically enabled for you when the library is initialized. This is required for certified operation of the modem.

Initialization

Now it's time to initialize the library. Here you can make a selection for the connectivity for the modem:

nrf_modem::init(SystemMode {
    lte_support: true,
    lte_psm_support: true,
    nbiot_support: true,
    gnss_support: true,
    preference: ConnectionPreference::None,
})
.await
.unwrap();

Now the library is ready to be used.

AT Commands

let response = nrf_modem::send_at::<64>("AT+CGMI").await.unwrap();
assert_eq!(response, "AT+CGMI\n\rNordic Semiconductor ASA\n\rOK\n\r");

DNS request

let google_ip = nrf_modem::get_host_by_name("www.google.com").await.unwrap();

Tcp connection

let stream = nrf_modem::TcpStream::connect(SocketAddr::from((google_ip, 80))).await.unwrap();

stream
    .write("GET / HTTP/1.0\nHost: google.com\r\n\r\n".as_bytes())
    .await
    .unwrap();

let mut buffer = [0; 1024];
let received = stream.receive(&mut buffer).await.unwrap();

println!("Google response: {}", core::str::from_utf8(received).unwrap());

// Drop the stream async (normal Drop is ok too, but that's blocking)
stream.deactivate().await.unwrap();

Udp socket

let socket =
    nrf_modem::UdpSocket::bind(SocketAddr::from_str("0.0.0.0:53").unwrap())
        .await
        .unwrap();

// Do a DNS request
socket
    .send_to(
        &[
            0xdb, 0x42, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x77,
            0x77, 0x77, 0x0C, 0x6E, 0x6F, 0x72, 0x74, 0x68, 0x65, 0x61, 0x73, 0x74, 0x65, 0x72,
            0x6E, 0x03, 0x65, 0x64, 0x75, 0x00, 0x00, 0x01, 0x00, 0x01,
        ],
        SocketAddr::from_str("8.8.8.8:53").unwrap(),
    )
    .await
    .unwrap();
let (response, source_addr) = socket.receive_from(&mut buffer).await.unwrap();

println!("Result: {:X}", response);
println!("Source: {}", source_addr);

Secure tcp connection over TLS

Before this can run, you need to store the required certificate in a security tag on the modem using AT commands. See the Nordic Docs on how to do this. TLS handshake will be much faster if you enforce an efficient cipher suite like TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256.

    let stream = nrf_modem::TlsStream::connect(
        "example.com",
        443,
        PeerVerification::Optional,
        &[ROOT_PEM],
        None,
    )
    .await
    .unwrap();

    stream
        .write("GET / HTTP/1.1\r\nHost: example.com\r\n\r\n".as_bytes())
        .await
        .unwrap();

    let mut buffer = [0; 1024];
    let received = stream
        .receive(&mut buffer)
        .await
        .unwrap();

    // Drop the stream async (normal Drop is ok too, but that's blocking)
    stream
        .deactivate().await.unwrap();