在舉行的第十九屆“開(kāi)源中國(guó)開(kāi)源世界”大會(huì)上，XIAOMI Lela 開(kāi)源負(fù)責(zé)人杜超宣布將對(duì)外公開(kāi)超過(guò)1000萬(wàn)行的 Xiaomi Vela 源碼。Xiaomi Vela 是小米基于開(kāi)源實(shí)時(shí)操作系統(tǒng) NuttX 打造的物聯(lián)網(wǎng)嵌入式軟件平臺(tái)，Vela 在各種物聯(lián)網(wǎng)硬件平臺(tái)上提供統(tǒng)一的軟件服務(wù)，支持豐富的組件和易用的框架，打通碎片化的物聯(lián)網(wǎng)應(yīng)用場(chǎng)景。
NuttX 運(yùn)行 Rust應(yīng)用
NuttX上豐富的基礎(chǔ)生態(tài)，與Rust的安全特性互相結(jié)合，是一個(gè)不錯(cuò)的方案，既能避免C開(kāi)發(fā)引發(fā)的潛在內(nèi)存問(wèn)題，又能結(jié)合Rust的安全和高效，快速完成安全的產(chǎn)品。目前有開(kāi)源的NuttX的Rust hal(https://github.com/lupyuen/nuttx-embedded-hal),該crate綁定了GPIO、I2C、SPI等常用外設(shè)。因此能在Rust代碼中調(diào)用NuttX的驅(qū)動(dòng)外設(shè)。下面展示一個(gè)簡(jiǎn)單的Rust代碼。
#![no_std] // Use the Rust Core Library instead of the Rust Standard Library, which is not compatible with embedded systems
extern "C" {
// 導(dǎo)入C的標(biāo)準(zhǔn)puts函數(shù)
fn puts(s: *const u8) -> i32;
}
#[no_mangle]
extern "C" fn rust_main() {
// Rust認(rèn)為任何來(lái)自C的接口都是非安全的，因此需要使用 unsafe包裹
unsafe {
// 打印字符到 NuttX 終端
puts(
b"Hello World!\0" // Byte String terminated with null
.as_ptr() // Convert to pointer
);
}
}在nuttx-embedded-hal庫(kù)中基于NuttX的POSIX接口寫(xiě)的Rust標(biāo)準(zhǔn)接口也非常方便。如SPI接口的部分實(shí)現(xiàn)如下。
/// NuttX SPI Struct
pub struct Spi {
/// NuttX File Descriptor
fd: i32,
}
/// NuttX Implementation of SPI Bus
impl Spi {
/// Create an SPI Bus from a Device Path (e.g. "/dev/spitest0")
pub fn new(path: &str) -> Result {
// Open the NuttX Device Path (e.g. "/dev/spitest0") for read-write
let fd = open(path, O_RDWR);
if fd < 0 { return Err(fd) }
// Return the SPI Bus
Ok(Self { fd })
}
}
/// NuttX Implementation of SPI Bus
impl Drop for Spi {
/// Close the SPI Bus
fn drop(&mut self) {
unsafe { close(self.fd) };
}
}
/// NuttX Implementation of SPI Write
impl spi::Write for Spi{
/// Error Type
type Error = i32;
/// Write SPI data
fn write(&mut self, words: &[u8]) -> Result<(), Self::Error> {
// Transmit data
let bytes_written = unsafe {
write(self.fd, words.as_ptr(), words.len() as u32)
};
assert_eq!(bytes_written, words.len() as i32);
Ok(())
}
}
/// NuttX Implementation of SPI Transfer
impl spi::Transfer for Spi {
/// Error Type
type Error = i32;
/// Transfer SPI data
fn transfer<'w>(&mut self, words: &'w mut [u8]) -> Result<&'w [u8], Self::Error> {
// Transmit data
let bytes_written = unsafe {
write(self.fd, words.as_ptr(), words.len() as u32)
};
assert_eq!(bytes_written, words.len() as i32);
// Read response
let bytes_read = unsafe {
read(self.fd, words.as_mut_ptr(), words.len() as u32)
};
assert_eq!(bytes_read, words.len() as i32);
// Return response
Ok(words)
}
} 使用也非常簡(jiǎn)單, 與Rust生的驅(qū)動(dòng)幾乎沒(méi)有差別。
// Import SPI Trait
use embedded_hal::blocking::spi;
// Open SPI Bus /dev/spitest0
let mut spi = nuttx_embedded_hal::Spi
::new("/dev/spitest0")
.expect("open spi failed");
// Open GPIO Output /dev/gpio1 for Chip Select
let mut cs = nuttx_embedded_hal::OutputPin
::new("/dev/gpio1")
.expect("open gpio failed");
// Set Chip Select to Low
cs.set_low()
.expect("cs failed");
// Transmit and receive SPI data
let mut data: [ u8; 5 ] = [ 0x1d, 0x00, 0x08, 0x00, 0x00 ];
spi.transfer(&mut data)
.expect("spi failed");
// Show the received SPI data
for i in 0..data.len() {
println!("{:02x}", data[i as usize]);
}
// Set Chip Select to High
cs.set_high()
.expect("cs failed"); 對(duì)于喜歡Rus語(yǔ)言的嵌入式工程師們來(lái)說(shuō)這是個(gè)非常棒的事情，再也不需要重新手搓寄存器來(lái)開(kāi)發(fā)驅(qū)動(dòng)，站在巨人的肩膀上開(kāi)發(fā)更有意思的應(yīng)用。
NuttX是一種輕量級(jí)的RTOS，嚴(yán)格遵守POSIX標(biāo)準(zhǔn)，廣泛應(yīng)用與各種控制器。從普通的8位的AVR單片機(jī)到arm、mips、risc-v、x86等各種架構(gòu)的芯片。常見(jiàn)的廠商如ST、NXP、GD、ESP等廠商都有適配的驅(qū)動(dòng)。由于嚴(yán)格遵從POSIX標(biāo)準(zhǔn)，因此對(duì)于不同的芯片，開(kāi)發(fā)方式都幾乎相同，同時(shí)一些Linux應(yīng)用也非常容易遷移到NuttX。