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Merge pull request embassy-rs#5333 from HybridChild/fix/stm32-i2c-v2-slave
stm32/i2c v2: Fix async slave implementation and return actual bytes transferred
2 parents ea1d944 + 8899dd0 commit 34b208d

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‎embassy-stm32/CHANGELOG.md‎

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@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
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<!-- next-header -->
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## Unreleased - ReleaseDate
1010

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- fix: stm32/i2c v2: Fix async slave by using DMA completion instead of TC flag for buffer-full detection
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- change: stm32/i2c v2: slave `respond_to_write` and `respond_to_read` now return actual bytes transferred instead of buffer size (breaking change, matching v1 behavior)
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- fix: stm32/i2c v1: `write_read` was losing last write byte before RESTART due to not waiting for BTF
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- fix: stm32/i2c v1: slave: async `respond_to_write` and `respond_to_read` now return actual bytes transferred instead of buffer size
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- fix: don't put USB pins into alternate mode on chips where USB is an additional function

‎embassy-stm32/src/i2c/v2.rs‎

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‎examples/stm32f0/src/bin/i2c_slave_async.rs‎

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//! I2C Async Slave Example
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//!
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//! Demonstrates the async I2C slave (multimaster) implementation using DMA.
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//! The device listens for I2C transactions from an external master.
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//!
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//! # Hardware Setup
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//!
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//! - PB8 (SCL) and PB9 (SDA) with 4.7k pull-up resistors to 3.3V
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//! - Connect an I2C master device with clock stretching enabled
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//! - Default slave address: 0x42 (7-bit)
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//!
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//! # Behavior
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//!
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//! - Master WRITE: Receives up to BUFFER_SIZE bytes via DMA, excess bytes are drained
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//! - Master READ: Sends an 8-byte response pattern (0xA0-0xA7) via DMA
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#![no_std]
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#![no_main]
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use defmt::*;
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use embassy_executor::Spawner;
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use embassy_stm32::i2c::{self, I2c, SendStatus, SlaveAddrConfig, SlaveCommandKind};
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use embassy_stm32::{bind_interrupts, dma, peripherals};
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use embassy_time::Duration;
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use {defmt_rtt as _, panic_probe as _};
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const I2C_ADDR: u8 = 0x42;
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const BUFFER_SIZE: usize = 32;
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bind_interrupts!(struct Irqs {
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I2C1 => i2c::EventInterruptHandler<peripherals::I2C1>, i2c::ErrorInterruptHandler<peripherals::I2C1>;
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DMA1_CHANNEL2_3 => dma::InterruptHandler<peripherals::DMA1_CH2>, dma::InterruptHandler<peripherals::DMA1_CH3>;
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});
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#[embassy_executor::main]
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async fn main(_spawner: Spawner) {
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let p = embassy_stm32::init(Default::default());
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info!("I2C Async Slave Example");
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info!("Address: 0x{:02X}, Buffer: {} bytes", I2C_ADDR, BUFFER_SIZE);
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let mut config = i2c::Config::default();
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config.timeout = Duration::from_secs(30);
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let mut i2c = I2c::new(p.I2C1, p.PB8, p.PB9, p.DMA1_CH2, p.DMA1_CH3, Irqs, config)
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.into_slave_multimaster(SlaveAddrConfig::basic(I2C_ADDR));
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info!("Slave ready, listening...");
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let mut count: u32 = 0;
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loop {
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match i2c.listen().await {
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Ok(cmd) => {
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count += 1;
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match cmd.kind {
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SlaveCommandKind::Write => {
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let mut buffer = [0u8; BUFFER_SIZE];
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match i2c.respond_to_write(&mut buffer).await {
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Ok(len) => info!("[{}] Write: {} bytes: {:02X}", count, len, &buffer[..len]),
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Err(e) => error!("[{}] Write error: {:?}", count, e),
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}
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}
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SlaveCommandKind::Read => {
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let response: [u8; 8] = [0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7];
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match i2c.respond_to_read(&response).await {
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Ok(SendStatus::Done) => info!("[{}] Read: {} bytes", count, response.len()),
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Ok(SendStatus::LeftoverBytes(n)) => {
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info!("[{}] Read: {} of {} bytes", count, response.len() - n, response.len())
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}
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Err(e) => error!("[{}] Read error: {:?}", count, e),
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}
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}
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}
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}
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Err(e) => error!("Listen error: {:?}", e),
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}
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}
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}

‎examples/stm32f0/src/bin/i2c_slave_blocking.rs‎

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//! I2C Blocking Slave Example
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//!
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//! Demonstrates the blocking I2C slave (multimaster) implementation.
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//! The device listens for I2C transactions from an external master.
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//!
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//! # Hardware Setup
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//!
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//! - PB8 (SCL) and PB9 (SDA) with 4.7k pull-up resistors to 3.3V
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//! - Connect an I2C master device with clock stretching enabled
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//! - Default slave address: 0x42 (7-bit)
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//!
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//! # Behavior
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//!
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//! - Master WRITE: Receives up to BUFFER_SIZE bytes, excess bytes are drained
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//! - Master READ: Sends an 8-byte response pattern (0xA0-0xA7)
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#![no_std]
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#![no_main]
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use defmt::*;
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use embassy_executor::Spawner;
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use embassy_stm32::i2c::{self, I2c, SendStatus, SlaveAddrConfig, SlaveCommandKind};
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use embassy_stm32::{bind_interrupts, peripherals};
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use embassy_time::Duration;
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use {defmt_rtt as _, panic_probe as _};
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const I2C_ADDR: u8 = 0x42;
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const BUFFER_SIZE: usize = 32;
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bind_interrupts!(struct Irqs {
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I2C1 => i2c::EventInterruptHandler<peripherals::I2C1>, i2c::ErrorInterruptHandler<peripherals::I2C1>;
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});
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#[embassy_executor::main]
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async fn main(_spawner: Spawner) {
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let p = embassy_stm32::init(Default::default());
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info!("I2C Blocking Slave Example");
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info!("Address: 0x{:02X}, Buffer: {} bytes", I2C_ADDR, BUFFER_SIZE);
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let mut config = i2c::Config::default();
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config.timeout = Duration::from_secs(30);
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let mut i2c =
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I2c::new_blocking(p.I2C1, p.PB8, p.PB9, config).into_slave_multimaster(SlaveAddrConfig::basic(I2C_ADDR));
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info!("Slave ready, listening...");
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let mut count: u32 = 0;
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loop {
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match i2c.blocking_listen() {
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Ok(cmd) => {
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count += 1;
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match cmd.kind {
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SlaveCommandKind::Write => {
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let mut buffer = [0u8; BUFFER_SIZE];
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match i2c.blocking_respond_to_write(&mut buffer) {
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Ok(len) => info!("[{}] Write: {} bytes: {:02X}", count, len, &buffer[..len]),
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Err(e) => error!("[{}] Write error: {:?}", count, e),
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}
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}
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SlaveCommandKind::Read => {
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let response: [u8; 8] = [0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7];
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match i2c.blocking_respond_to_read(&response) {
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Ok(SendStatus::Done) => info!("[{}] Read: {} bytes", count, response.len()),
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Ok(SendStatus::LeftoverBytes(n)) => {
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info!("[{}] Read: {} of {} bytes", count, response.len() - n, response.len())
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}
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Err(e) => error!("[{}] Read error: {:?}", count, e),
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}
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}
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}
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}
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Err(e) => error!("Listen error: {:?}", e),
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}
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}
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}

‎examples/stm32f072/.cargo/config.toml‎

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[target.thumbv6m-none-eabi]
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runner = 'probe-rs run --chip STM32F072RB'
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[build]
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target = "thumbv6m-none-eabi"
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[env]
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DEFMT_LOG = "trace"

‎examples/stm32f072/Cargo.toml‎

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[package]
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name = "embassy-stm32f0-examples"
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version = "0.1.0"
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edition = "2024"
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license = "MIT OR Apache-2.0"
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publish = false
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[dependencies]
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# Change stm32f091rc to your chip name, if necessary.
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embassy-stm32 = { version = "0.5.0", path = "../../embassy-stm32", features = [ "defmt", "memory-x", "stm32f072rb", "time-driver-tim2", "exti", "unstable-pac"] }
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cortex-m = { version = "0.7.6", features = ["inline-asm", "critical-section-single-core"] }
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cortex-m-rt = "0.7.0"
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defmt = "1.0.1"
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defmt-rtt = "1.0.0"
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panic-probe = { version = "1.0.0", features = ["print-defmt"] }
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embassy-sync = { version = "0.7.2", path = "../../embassy-sync", features = ["defmt"] }
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embassy-executor = { version = "0.9.0", path = "../../embassy-executor", features = ["arch-cortex-m", "executor-thread", "executor-interrupt", "defmt"] }
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embassy-time = { version = "0.5.0", path = "../../embassy-time", features = ["defmt", "defmt-timestamp-uptime", "tick-hz-32_768"] }
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embassy-futures = { version = "0.1.0", path = "../../embassy-futures" }
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embedded-hal-1 = { package = "embedded-hal", version = "1.0" }
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static_cell = "2"
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portable-atomic = { version = "1.5", features = ["unsafe-assume-single-core"] }
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[profile.release]
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debug = 2
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[package.metadata.embassy]
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build = [
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{ target = "thumbv6m-none-eabi", artifact-dir = "out/examples/stm32f0" }
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]

‎examples/stm32f072/build.rs‎

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fn main() {
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println!("cargo:rustc-link-arg-bins=--nmagic");
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println!("cargo:rustc-link-arg-bins=-Tlink.x");
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println!("cargo:rustc-link-arg-bins=-Tdefmt.x");
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}

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