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Finomnis's questions

Martin Hope
Finomnis
Asked: 2023-12-05 20:08:01 +0800 CST
  • 6

我正在实现 SPI 驱动程序。

现在我有以下驱动程序代码（MRE 化）：

use tokio::{join, sync::mpsc};

async fn spi_transmit(write_buf: &[u32], read_buf: &mut [u32]) {
    assert_eq!(read_buf.len(), write_buf.len());
    let (write_fifo, mut read_fifo) = mpsc::channel(2);

    let write_task = async {
        // Simulate an SPI bus that respondes with the sent data + 20,
        // just for demo purposes
        for val in write_buf {
            write_fifo.send(*val + 20).await.unwrap();
        }
    };

    let read_task = async {
        for val in read_buf {
            *val = read_fifo.recv().await.unwrap();
        }
    };

    join!(write_task, read_task);
}

#[tokio::main]
async fn main() {
    let buf_out = [1, 2, 3, 4];
    let mut buf_in = [0, 0, 0, 0];

    spi_transmit(&buf_out, &mut buf_in).await;

    println!("{:?}", buf_in);
}

[21, 22, 23, 24]

中央 API 是async fn spi_transmit(write_buf: &[u32], read_buf: &mut [u32]).

现在我需要实现一个async fn spi_transmit_in_place(read_write_buf: &mut [u32])从同一个缓冲区发送和接收的缓冲区，该缓冲区最终包含读取的数据。

我知道对缓冲区的读写访问永远不会重叠，总是先读取一个字节，然后在稍后的非重叠时间写入它。

有了这些知识，如果我这样实现它是否被认为是合理的，或者这被认为是未定义的行为？

async fn spi_transmit_in_place(read_write_buf: &mut [u32]) {
    let write_buf = unsafe {
        let data = read_write_buf.as_ptr();
        let len = read_write_buf.len();
        std::slice::from_raw_parts(data, len)
    };

    spi_transmit(write_buf, read_write_buf).await
}

#[tokio::main]
async fn main() {
    let mut buf = [1, 2, 3, 4];
    spi_transmit_in_place(&mut buf).await;
    println!("{:?}", buf);
}

[21, 22, 23, 24]

它有效，但miri 不高兴。

spi_transmit如果这是未定义的行为，这是否意味着我必须使用原始指针重新实现？或者我还能怎样解决这个问题？

rust