nrf-softdevice
Rust bindings for Nordic Semiconductor nRF series SoftDevices.
SoftDevices are a closed source C binary written by Nordic for their microcontrollers that sits at the bottom of flash and is called first on startup. The softdevice then calls your application or bootloader or whatever is sitting directly after it in flash.
They are full featured, battle tested, and pre qualified for bluetooth certification and thus make valuable bluetooth stacks when bindgened to Rust -- at least until we get a Rust bluetooth stack certified to be shipped commercially. Different SoftDevices support specific chips as well as certain features, like working only as a peripheral, or both a peripheral and central, or even offer alternate radio configuration like ant.
Besides the handicap of being closed source, the cost of SoftDevices is they steal away resources like ram and flash as well as timer peripherals and several priorities of interrupts from your application.
High-level bindings
The nrf-softdevice
crate contains high-level easy-to-use Rust async/await bindings for the Softdevice.
Working:
- Safe interrupt management
- Async flash API
- Bluetooth central (scanning and connecting)
- Bluetooth peripheral (advertising, connectable-only for now)
- GATT client
- GATT server
- L2CAP Connection-Oriented channels
- Data length extension
- ATT MTU extension
- Get/set own BLE address
To use it you must specify the following Cargo features:
- exactly one softdevice model, for example feature
s140
. - exactly one supported nRF chip model, for example feature
nrf52840
.
The following softdevices are supported.
- S112 (peripheral only)
- S113 (peripheral only)
- S122 (central only)
- S132 (central and peripheral)
- S140 v7.x.x (central and peripheral)
The following nRF chips are supported
- nRF52810
- nRF52832
- nRF52833
- nRF52840
Some softdevices support only some chips, check Nordic's documentation for details.
Setting up your build environment
This project uses new toolchain features, often only to be found in nightly. Please ensure that your toolchains are up to date:
rustup update
You will also need probe-run
- a utility to enable cargo run
to run embedded applications on a device:
cargo install probe-run
Running examples
The following instructions are for the S140 and nRF52840-DK. You may have to adjust accordingly and can do so by modifying the cargo.toml
of the examples folder -
please check out the nrf-softdevice
and nrf-softdevice-s140
dependency declarations.
Flashing the softdevice is required. It is NOT part of the built binary. You only need to do it once at the beginning, or after doing full chip erases.
- Download SoftDevice S140 from Nordic's website here. Supported versions are 7.x.x
- Unzip
- As a debug client, if you are using
- probe-rs:
- Erase the flash with
probe-rs-cli erase --chip nrf52840
- Flash the SoftDevice with
probe-rs-cli download --chip nrf52840 --format hex s140_nrf52_7.X.X_softdevice.hex
- Erase the flash with
- nrfjprog:
- Flash the SoftDevice with
nrfjprog --family NRF52 --chiperase --verify --program s140_nrf52_7.0.1_softdevice.hex
- Flash the SoftDevice with
- probe-rs:
To run an example, simply use cargo run
from the examples
folder:
cd examples && cargo run --bin ble_bas_peripheral
Configuring a SoftDevice
The first thing to do is find out how much flash the SoftDevice you've chosen uses. Look in the release notes, or google for your SoftDevice version and "memory map". For an s132 v7.3 its listed as 0x26000, or in human readable numbers 152K (0x26000 in hex is 155648 in decimal / 1024 bytes = 152K)
Set the memory.x to move your applications flash start to after the SoftDevice size and subtract it from the total available size:
MEMORY
{
/* NOTE 1 K = 1 KiBi = 1024 bytes */
/* These values correspond to the NRF52832 with SoftDevices S132 7.3.0 */
FLASH : ORIGIN = 0x00000000 + 152K, LENGTH = 512K - 152K
RAM : ORIGIN = 0x20000000 + 44K, LENGTH = 64K - 44K
}
You can pick mostly anything for ram right now as if you have defmt logging enabled, the SoftDevice will tell you what the right number is when you call enable:
1 INFO softdevice RAM: 41600 bytes
└─ nrf_softdevice::softdevice::{impl#0}::enable @ /home/jacob/.cargo/git/checkouts/nrf-softdevice-03ef4aef10e777e4/fa369be/nrf-softdevice/src/fmt.rs:138
2 ERROR panicked at 'too little RAM for softdevice. Change your app's RAM start address to 2000a280'
You have some control over that number by tweaking the SoftDevice configuration parameters. See especially the concurrent connection parameters. If you dont need to support multiple connections these can really decrease your ram size:
- conn_gap.conn_count The number of concurrent connections the application can create with this configuration
- periph_role_count Maximum number of connections concurrently acting as a peripheral
- central_role_count Maximum number of connections concurrently acting as a central
Next you need to find out if your board has an external oscillator (which provides better battery life) But if in doubt just assume it doesn't and set the SoftDevice to use an internal clock. A common no external crystal configuration for nRF52 might be
clock: Some(raw::nrf_clock_lf_cfg_t {
source: raw::NRF_CLOCK_LF_SRC_RC as u8,
rc_ctiv: 16,
rc_temp_ctiv: 2,
accuracy: raw::NRF_CLOCK_LF_ACCURACY_500_PPM as u8,
}),
Interrupts
The SoftDevice does time-critical radio processing at high priorities. If its timing is disrupted, it will raise "assertion failed" errors. There's two common mistakes to avoid: (temporarily) disabling the softdevice's interrupts, and running your interrupts at too high priority.
These mistakes WILL cause "assertion failed" errors, 100% guaranteed. If you do these only "a little bit", such as disabling all interrupts but for very short periods of time only, things may appear to work, but you will get "assertion failed" errors after hours of running. Make sure to follow them to the letter.
The Softdevice Driver (e.g. Softdevice::run()
) cannot be used from interrupts by default. However, the usable-from-interrupts
feature enables this functionality. To use this feature, a critical-section
implementation is required.
This crate's internal implementation (critical-section-impl
feature) is recommended, but other Softdevice-compatible implementations should also work.
Critical sections
Interrupts for certain peripherals and SWI/EGUs are reserved for the SoftDevice. Interrupt handlers for them are reserved by the softdevice, the handlers in your application won't be called.
DO NOT disable the softdevice's interrupts. You MUST NOT use the widely-used cortex_m::interrupt::free
for "disable all interrupts" critical sections. Instead, use the critical-section
crate, which allows custom critical-section implementations:
- Make sure the
critical-section-impl
Cargo feature is enabled fornrf-softdevice
. This makesnrf-softdevice
emit a custom critical section implementation that disables only non-softdevice interrupts. - Use
critical_section::with
instead ofcortex_m::interrupt::free
. This uses the custom critical-section impl. - Use
embassy_sync::blocking_mutex::CriticalSectionMutex
instead ofcortex_m::interrupt::Mutex
.
Make sure you're not using any library that internally uses cortex_m::interrupt::free
as well.
Interrupt priority
Interrupt priority levels 0, 1, and 4 are reserved for the SoftDevice. Make sure to not use them.
The default priority level for interrupts is 0, so for every single interrupt you enable, make sure to set the priority level explicitly. For example:
use embassy_nrf::interrupt::{self, InterruptExt};
interrupt::SPIM3.set_priority(interrupt::Priority::P3);
let mut spim = spim::Spim::new(p.SPI3, Irqs, p.P0_13, p.P0_16, p.P0_15, config);
If you're using embassy-nrf
with the gpiote
or time-driver-rtc1
features enabled, you'll need to edit your embassy_config to move those priorities:
// 0 is Highest. Lower prio number can preempt higher prio number
// Softdevice has reserved priorities 0, 1 and 4
let mut config = embassy_nrf::config::Config::default();
config.gpiote_interrupt_priority = Priority::P2;
config.time_interrupt_priority = Priority::P2;
let peripherals = embassy_nrf::init(config);
Troubleshooting
If you are sure you have set interrupts correctly, but are still getting an error like below:
[ERROR]Location<lib.rs:104>panicked at 'sd_softdevice_enable err SdmIncorrectInterruptConfiguration'
Make sure the defmt
feature is enabled on embassy_nrf
.
You can then use this code to print whether an interrupt is enabled, and its priority:
for num in 0..48 {
let interrupt = unsafe { mem::transmute::<u16, Interrupt>(num) };
let is_enabled = InterruptExt::is_enabled(interrupt);
let priority = InterruptExt::get_priority(interrupt);
println!("Interrupt {}: Enabled = {}, Priority = {}", num, is_enabled, priority);
}
Interrupt numbers map to what they are in the Interrupt
enum.
If your SoftDevice is hardfaulting on enable and you think you have everything right, make sure to go back and do a full chip erase or recover, and reflash the SoftDevice again. A few bytes of empty space after the SoftDevice are required to be 0xFF, but might not be if the softdevice was flashed over an existing binary.
If the following linking error occurs
rust-lld: error: undefined symbol: _critical_section_release
make sure the feature critical-section-impl
is enabled and also that the softdevice is included in the code, e.g. use nrf_softdevice as _;
.
If running the firmware timeouts after flashing, make sure the size and location of the RAM and FLASH region in the linker script is correct.
Low-level raw bindings
The nrf-softdevice-s1xx
crates contain low-level bindings, matching 1-1 with the softdevice C headers.
They are generated with bindgen
, with extra post-processing to correctly generate the svc
-based softdevice calls.
Generated code consists of inline functions using inline ASM, ensuring the lowest possible
overhead. Most of the times you'll see them inlined as a single svc
instruction in the
calling function. Here is an example:
#[inline(always)]
pub unsafe fn sd_ble_gap_connect(
p_peer_addr: *const ble_gap_addr_t,
p_scan_params: *const ble_gap_scan_params_t,
p_conn_params: *const ble_gap_conn_params_t,
conn_cfg_tag: u8,
) -> u32 {
let ret: u32;
core::arch::asm!("svc 140",
inout("r0") p_peer_addr => res,
inout("r1") p_scan_params => _,
inout("r2") p_conn_params => _,
inout("r3") conn_cfg_tag => _,
lateout("r12") _,
);
ret
}
Generating
The bindings are generated from the headers with the gen.sh
script.
License
This repo includes the softdevice headers, which are licensed under Nordic's proprietary license.
Generated binding.rs
files are a derived work of the headers, so they are also subject to Nordic's license.
The high level bindings (nrf-softdevice) and the generator code (nrf-softdevice-gen) are licensed under either of
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.