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Move EasyDMA documentation to module level

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Til Blechschmidt 2022-03-08 16:42:46 +01:00
parent 7540b44050
commit 63030bf998
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GPG Key ID: 2F4E54D35C8390CB
4 changed files with 53 additions and 38 deletions
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36
embassy-nrf/src/lib.rs
View File

@ -1,3 +1,39 @@
//! ## EasyDMA considerations
//!
//! On nRF chips, peripherals can use the so called EasyDMA feature to offload the task of interacting
//! with peripherals. It takes care of sending/receiving data over a variety of bus protocols (TWI/I2C, UART, SPI).
//! However, EasyDMA requires the buffers used to transmit and receive data to reside in RAM. Unfortunately, Rust
//! slices will not always do so. The following example using the SPI peripheral shows a common situation where this might happen:
//!
//! ```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, Err(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 peripheral struct which uses EasyDMA ([`Spim`](spim::Spim), [`Uarte`](uarte::Uarte), [`Twim`](twim::Twim)) has two variants of their mutating functions:
//! - 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. Be aware that this overhead is not only in terms of instruction count but also in terms of memory usage
//! as the methods without the suffix will be allocating a statically sized buffer (up to 512 bytes for the nRF52840).
//!
//! Note that the methods that read data like [`read`](spim::Spim::read) and [`transfer_in_place`](spim::Spim::transfer_in_place) do not have the corresponding `_from_ram` variants as
//! mutable slices always reside in RAM.
#![no_std]
#![cfg_attr(
feature = "nightly",

41
embassy-nrf/src/spim.rs
View File

@ -31,38 +31,7 @@ pub enum Error {
/// 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.
/// For more details about EasyDMA, consult the module documentation.
pub struct Spim<'d, T: Instance> {
phantom: PhantomData<&'d mut T>,
}
@ -325,7 +294,7 @@ impl<'d, T: Instance> Spim<'d, T> {
self.blocking_inner(read, write)
}
/// Same as [`blocking_transfer`](Spim::blocking_transfer) but will fail instead of copying data into RAM.
/// Same as [`blocking_transfer`](Spim::blocking_transfer) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub fn blocking_transfer_from_ram(
&mut self,
read: &mut [u8],
@ -346,7 +315,7 @@ impl<'d, T: Instance> Spim<'d, T> {
self.blocking_inner(&mut [], data)
}
/// Same as [`blocking_write`](Spim::blocking_write) but will fail instead of copying data into RAM.
/// Same as [`blocking_write`](Spim::blocking_write) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub fn blocking_write_from_ram(&mut self, data: &[u8]) -> Result<(), Error> {
self.blocking_inner(&mut [], data)
}
@ -362,7 +331,7 @@ impl<'d, T: Instance> Spim<'d, T> {
self.async_inner(read, write).await
}
/// Same as [`transfer`](Spim::transfer) but will fail instead of copying data into RAM.
/// Same as [`transfer`](Spim::transfer) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub async fn transfer_from_ram(&mut self, read: &mut [u8], write: &[u8]) -> Result<(), Error> {
self.async_inner_from_ram(read, write).await
}
@ -378,7 +347,7 @@ impl<'d, T: Instance> Spim<'d, T> {
self.async_inner(&mut [], data).await
}
/// Same as [`write`](Spim::write) but will fail instead of copying data into RAM.
/// Same as [`write`](Spim::write) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub async fn write_from_ram(&mut self, data: &[u8]) -> Result<(), Error> {
self.async_inner_from_ram(&mut [], data).await
}

8
embassy-nrf/src/twim.rs
View File

@ -64,7 +64,9 @@ pub enum Error {
Overrun,
}
/// Interface to a TWIM instance.
/// Interface to a TWIM instance using EasyDMA to offload the transmission and reception workload.
///
/// For more details about EasyDMA, consult the module documentation.
pub struct Twim<'d, T: Instance> {
phantom: PhantomData<&'d mut T>,
}
@ -432,6 +434,7 @@ impl<'d, T: Instance> Twim<'d, T> {
Ok(())
}
/// Same as [`blocking_write`](Twim::blocking_write) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub fn blocking_write_from_ram(&mut self, address: u8, buffer: &[u8]) -> Result<(), Error> {
self.setup_write_from_ram(address, buffer, false)?;
self.blocking_wait();
@ -474,6 +477,7 @@ impl<'d, T: Instance> Twim<'d, T> {
Ok(())
}
/// Same as [`blocking_write_read`](Twim::blocking_write_read) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub fn blocking_write_read_from_ram(
&mut self,
address: u8,
@ -507,6 +511,7 @@ impl<'d, T: Instance> Twim<'d, T> {
Ok(())
}
/// Same as [`write`](Twim::write) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub async fn write_from_ram(&mut self, address: u8, buffer: &[u8]) -> Result<(), Error> {
self.setup_write_from_ram(address, buffer, true)?;
self.async_wait().await;
@ -531,6 +536,7 @@ impl<'d, T: Instance> Twim<'d, T> {
Ok(())
}
/// Same as [`write_read`](Twim::write_read) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub async fn write_read_from_ram(
&mut self,
address: u8,

6
embassy-nrf/src/uarte.rs
View File

@ -60,7 +60,9 @@ pub enum Error {
// TODO: add other error variants.
}
/// Interface to the UARTE peripheral
/// Interface to the UARTE peripheral using EasyDMA to offload the transmission and reception workload.
///
/// For more details about EasyDMA, consult the module documentation.
pub struct Uarte<'d, T: Instance> {
phantom: PhantomData<&'d mut T>,
tx: UarteTx<'d, T>,
@ -224,6 +226,7 @@ impl<'d, T: Instance> Uarte<'d, T> {
self.tx.write(buffer).await
}
/// Same as [`write`](Uarte::write) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub async fn write_from_ram(&mut self, buffer: &[u8]) -> Result<(), Error> {
self.tx.write_from_ram(buffer).await
}
@ -236,6 +239,7 @@ impl<'d, T: Instance> Uarte<'d, T> {
self.tx.blocking_write(buffer)
}
/// Same as [`blocking_write`](Uarte::blocking_write) but will fail instead of copying data into RAM. Consult the module level documentation to learn more.
pub fn blocking_write_from_ram(&mut self, buffer: &[u8]) -> Result<(), Error> {
self.tx.blocking_write_from_ram(buffer)
}