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Change SPIM methods to copy slice if required and add non-copying variants

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This commit is contained in:
Til Blechschmidt
2022-02-23 22:51:59 +01:00
parent ed9fad8c7e
commit e96dd3654a
1 changed files with 99 additions and 6 deletions
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105
embassy-nrf/src/spim.rs
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@@ -28,6 +28,40 @@ pub enum Error {
DMABufferNotInDataMemory,
}
/// Interface for the SPIM peripheral using EasyDMA to offload the transmission and reception workload.
///
/// ## Data locality requirements
///
/// On nRF chips, EasyDMA requires the buffers to reside in RAM. However, Rust
/// slices will not always do so. Take the following example:
///
/// ```no_run
/// // As we pass a slice to the function whose contents will not ever change,
/// // the compiler writes it into the flash and thus the pointer to it will
/// // reference static memory. Since EasyDMA requires slices to reside in RAM,
/// // this function call will fail.
/// let result = spim.write_from_ram(&[1, 2, 3]);
/// assert_eq!(result, Error::DMABufferNotInDataMemory);
///
/// // The data is still static and located in flash. However, since we are assigning
/// // it to a variable, the compiler will load it into memory. Passing a reference to the
/// // variable will yield a pointer that references dynamic memory, thus making EasyDMA happy.
/// // This function call succeeds.
/// let data = [1, 2, 3];
/// let result = spim.write_from_ram(&data);
/// assert!(result.is_ok());
/// ```
///
/// Each function in this struct has a `_from_ram` variant and one without this suffix.
/// - Functions with the suffix (e.g. [`write_from_ram`](Spim::write_from_ram), [`transfer_from_ram`](Spim::transfer_from_ram)) will return an error if the passed slice does not reside in RAM.
/// - Functions without the suffix (e.g. [`write`](Spim::write), [`transfer`](Spim::transfer)) will check whether the data is in RAM and copy it into memory prior to transmission.
///
/// Since copying incurs a overhead, you are given the option to choose from `_from_ram` variants which will
/// fail and notify you, or the more convenient versions without the suffix which are potentially a little bit
/// more inefficient.
///
/// Note that the [`read`](Spim::read) and [`transfer_in_place`](Spim::transfer_in_place) methods do not have the corresponding `_from_ram` variants as
/// mutable slices always reside in RAM.
pub struct Spim<'d, T: Instance> {
phantom: PhantomData<&'d mut T>,
}
@@ -223,7 +257,7 @@ impl<'d, T: Instance> Spim<'d, T> {
Ok(())
}
fn blocking_inner(&mut self, rx: *mut [u8], tx: *const [u8]) -> Result<(), Error> {
fn blocking_inner_from_ram(&mut self, rx: *mut [u8], tx: *const [u8]) -> Result<(), Error> {
self.prepare(rx, tx)?;
// Wait for 'end' event.
@@ -234,7 +268,18 @@ impl<'d, T: Instance> Spim<'d, T> {
Ok(())
}
async fn async_inner(&mut self, rx: *mut [u8], tx: *const [u8]) -> Result<(), Error> {
fn blocking_inner(&mut self, rx: &mut [u8], tx: &[u8]) -> Result<(), Error> {
match self.blocking_inner_from_ram(rx, tx) {
Ok(_) => Ok(()),
Err(Error::DMABufferNotInDataMemory) => {
let tx_copied = tx.clone();
self.blocking_inner_from_ram(rx, tx_copied)
}
Err(error) => Err(error),
}
}
async fn async_inner_from_ram(&mut self, rx: *mut [u8], tx: *const [u8]) -> Result<(), Error> {
self.prepare(rx, tx)?;
// Wait for 'end' event.
@@ -253,37 +298,85 @@ impl<'d, T: Instance> Spim<'d, T> {
Ok(())
}
async fn async_inner(&mut self, rx: &mut [u8], tx: &[u8]) -> Result<(), Error> {
match self.async_inner_from_ram(rx, tx).await {
Ok(_) => Ok(()),
Err(Error::DMABufferNotInDataMemory) => {
let tx_copied = tx.clone();
self.async_inner_from_ram(rx, tx_copied).await
}
Err(error) => Err(error),
}
}
/// Reads data from the SPI bus without sending anything. Blocks until the buffer has been filled.
pub fn blocking_read(&mut self, data: &mut [u8]) -> Result<(), Error> {
self.blocking_inner(data, &[])
}
/// Simultaneously sends and receives data. Blocks until the transmission is completed.
/// If necessary, the write buffer will be copied into RAM (see struct description for detail).
pub fn blocking_transfer(&mut self, read: &mut [u8], write: &[u8]) -> Result<(), Error> {
self.blocking_inner(read, write)
}
pub fn blocking_transfer_in_place(&mut self, data: &mut [u8]) -> Result<(), Error> {
self.blocking_inner(data, data)
/// Same as [`blocking_transfer`](Spim::blocking_transfer) but will fail instead of copying data into RAM.
pub fn blocking_transfer_from_ram(
&mut self,
read: &mut [u8],
write: &[u8],
) -> Result<(), Error> {
self.blocking_inner(read, write)
}
/// Simultaneously sends and receives data.
/// Places the received data into the same buffer and blocks until the transmission is completed.
pub fn blocking_transfer_in_place(&mut self, data: &mut [u8]) -> Result<(), Error> {
self.blocking_inner_from_ram(data, data)
}
/// Sends data, discarding any received data. Blocks until the transmission is completed.
/// If necessary, the write buffer will be copied into RAM (see struct description for detail).
pub fn blocking_write(&mut self, data: &[u8]) -> Result<(), Error> {
self.blocking_inner(&mut [], data)
}
/// Same as [`blocking_write`](Spim::blocking_write) but will fail instead of copying data into RAM.
pub fn blocking_write_from_ram(&mut self, data: &[u8]) -> Result<(), Error> {
self.blocking_inner(&mut [], data)
}
/// Reads data from the SPI bus without sending anything.
pub async fn read(&mut self, data: &mut [u8]) -> Result<(), Error> {
self.async_inner(data, &[]).await
}
/// Simultaneously sends and receives data.
/// If necessary, the write buffer will be copied into RAM (see struct description for detail).
pub async fn transfer(&mut self, read: &mut [u8], write: &[u8]) -> Result<(), Error> {
self.async_inner(read, write).await
}
pub async fn transfer_in_place(&mut self, data: &mut [u8]) -> Result<(), Error> {
self.async_inner(data, data).await
/// Same as [`transfer`](Spim::transfer) but will fail instead of copying data into RAM.
pub async fn transfer_from_ram(&mut self, read: &mut [u8], write: &[u8]) -> Result<(), Error> {
self.async_inner_from_ram(read, write).await
}
/// Simultaneously sends and receives data. Places the received data into the same buffer.
pub async fn transfer_in_place(&mut self, data: &mut [u8]) -> Result<(), Error> {
self.async_inner_from_ram(data, data).await
}
/// Sends data, discarding any received data.
/// If necessary, the write buffer will be copied into RAM (see struct description for detail).
pub async fn write(&mut self, data: &[u8]) -> Result<(), Error> {
self.async_inner(&mut [], data).await
}
/// Same as [`write`](Spim::write) but will fail instead of copying data into RAM.
pub async fn write_from_ram(&mut self, data: &[u8]) -> Result<(), Error> {
self.async_inner_from_ram(&mut [], data).await
}
}
impl<'d, T: Instance> Drop for Spim<'d, T> {