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Merge #640

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640: Skip EasyDMA slice location check for empty slices and copy data if necessary r=Dirbaio a=TilBlechschmidt

As discussed, this PR makes the following changes:
- Ignore pointer location of zero-length slices (fixes #631)
- Change default functions so they copy the tx buffer if it does not reside in RAM
- Introduce new variants for `write`, `transfer`, and their blocking versions which fails instead of copying
- Add documentation about the motivation behind all these variants
<img width="984" alt="image" src="https://user-images.githubusercontent.com/5037967/155415788-c2cd1055-9289-4004-959d-be3b1934a439.png">


Remaining TODOs:

- [x] Change copying behaviour for other peripherals
    - [x] TWI
    - [x] UART
- [x] Add module-level documentation regarding EasyDMA and `_from_ram` method variants

`@Dirbaio` it probably makes sense for you to review it now before I "copy" over the changes to the other two peripherals.

Co-authored-by: Til Blechschmidt <til@blechschmidt.de>
This commit is contained in:
bors[bot] 2022-03-09 01:47:52 +00:00 committed by GitHub
commit 13247897b0
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5 changed files with 240 additions and 52 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",

79
embassy-nrf/src/spim.rs
View File

@ -8,6 +8,7 @@ use embassy::util::Unborrow;
use embassy_hal_common::unborrow;
use futures::future::poll_fn;
use crate::chip::FORCE_COPY_BUFFER_SIZE;
use crate::gpio::sealed::Pin as _;
use crate::gpio::{self, AnyPin};
use crate::gpio::{Pin as GpioPin, PselBits};
@ -28,6 +29,9 @@ pub enum Error {
DMABufferNotInDataMemory,
}
/// Interface for the SPIM peripheral using EasyDMA to offload the transmission and reception workload.
///
/// For more details about EasyDMA, consult the module documentation.
pub struct Spim<'d, T: Instance> {
phantom: PhantomData<&'d mut T>,
}
@ -223,7 +227,7 @@ 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 +238,20 @@ 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) => {
trace!("Copying SPIM tx buffer into RAM for DMA");
let tx_ram_buf = &mut [0; FORCE_COPY_BUFFER_SIZE][..tx.len()];
tx_ram_buf.copy_from_slice(tx);
self.blocking_inner_from_ram(rx, tx_ram_buf)
}
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 +270,87 @@ 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) => {
trace!("Copying SPIM tx buffer into RAM for DMA");
let tx_ram_buf = &mut [0; FORCE_COPY_BUFFER_SIZE][..tx.len()];
tx_ram_buf.copy_from_slice(tx);
self.async_inner_from_ram(rx, tx_ram_buf).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. Consult the module level documentation to learn more.
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. 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)
}
/// 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. 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
}
/// 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. 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
}
}
impl<'d, T: Instance> Drop for Spim<'d, T> {

128
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>,
}
@ -287,7 +289,12 @@ impl<'d, T: Instance> Twim<'d, T> {
})
}
fn setup_write(&mut self, address: u8, buffer: &[u8], inten: bool) -> Result<(), Error> {
fn setup_write_from_ram(
&mut self,
address: u8,
buffer: &[u8],
inten: bool,
) -> Result<(), Error> {
let r = T::regs();
compiler_fence(SeqCst);
@ -342,7 +349,7 @@ impl<'d, T: Instance> Twim<'d, T> {
Ok(())
}
fn setup_write_read(
fn setup_write_read_from_ram(
&mut self,
address: u8,
wr_buffer: &[u8],
@ -382,6 +389,38 @@ impl<'d, T: Instance> Twim<'d, T> {
Ok(())
}
fn setup_write_read(
&mut self,
address: u8,
wr_buffer: &[u8],
rd_buffer: &mut [u8],
inten: bool,
) -> Result<(), Error> {
match self.setup_write_read_from_ram(address, wr_buffer, rd_buffer, inten) {
Ok(_) => Ok(()),
Err(Error::DMABufferNotInDataMemory) => {
trace!("Copying TWIM tx buffer into RAM for DMA");
let tx_ram_buf = &mut [0; FORCE_COPY_BUFFER_SIZE][..wr_buffer.len()];
tx_ram_buf.copy_from_slice(wr_buffer);
self.setup_write_read_from_ram(address, &tx_ram_buf, rd_buffer, inten)
}
Err(error) => Err(error),
}
}
fn setup_write(&mut self, address: u8, wr_buffer: &[u8], inten: bool) -> Result<(), Error> {
match self.setup_write_from_ram(address, wr_buffer, inten) {
Ok(_) => Ok(()),
Err(Error::DMABufferNotInDataMemory) => {
trace!("Copying TWIM tx buffer into RAM for DMA");
let tx_ram_buf = &mut [0; FORCE_COPY_BUFFER_SIZE][..wr_buffer.len()];
tx_ram_buf.copy_from_slice(wr_buffer);
self.setup_write_from_ram(address, &tx_ram_buf, inten)
}
Err(error) => Err(error),
}
}
/// Write to an I2C slave.
///
/// The buffer must have a length of at most 255 bytes on the nRF52832
@ -395,6 +434,16 @@ 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();
compiler_fence(SeqCst);
self.check_errorsrc()?;
self.check_tx(buffer.len())?;
Ok(())
}
/// Read from an I2C slave.
///
/// The buffer must have a length of at most 255 bytes on the nRF52832
@ -428,45 +477,20 @@ impl<'d, T: Instance> Twim<'d, T> {
Ok(())
}
/// Copy data into RAM and write to an I2C slave.
///
/// The write buffer must have a length of at most 255 bytes on the nRF52832
/// and at most 1024 bytes on the nRF52840.
pub fn blocking_copy_write(&mut self, address: u8, wr_buffer: &[u8]) -> Result<(), Error> {
if wr_buffer.len() > FORCE_COPY_BUFFER_SIZE {
return Err(Error::TxBufferTooLong);
}
// Copy to RAM
let wr_ram_buffer = &mut [0; FORCE_COPY_BUFFER_SIZE][..wr_buffer.len()];
wr_ram_buffer.copy_from_slice(wr_buffer);
self.blocking_write(address, wr_ram_buffer)
}
/// Copy data into RAM and write to an I2C slave, then read data from the slave without
/// triggering a stop condition between the two.
///
/// The write buffer must have a length of at most 255 bytes on the nRF52832
/// and at most 1024 bytes on the nRF52840.
///
/// The read buffer must have a length of at most 255 bytes on the nRF52832
/// and at most 65535 bytes on the nRF52840.
pub fn blocking_copy_write_read(
/// 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,
wr_buffer: &[u8],
rd_buffer: &mut [u8],
) -> Result<(), Error> {
if wr_buffer.len() > FORCE_COPY_BUFFER_SIZE {
return Err(Error::TxBufferTooLong);
}
// Copy to RAM
let wr_ram_buffer = &mut [0; FORCE_COPY_BUFFER_SIZE][..wr_buffer.len()];
wr_ram_buffer.copy_from_slice(wr_buffer);
self.blocking_write_read(address, wr_ram_buffer, rd_buffer)
self.setup_write_read_from_ram(address, wr_buffer, rd_buffer, false)?;
self.blocking_wait();
compiler_fence(SeqCst);
self.check_errorsrc()?;
self.check_tx(wr_buffer.len())?;
self.check_rx(rd_buffer.len())?;
Ok(())
}
pub async fn read(&mut self, address: u8, buffer: &mut [u8]) -> Result<(), Error> {
@ -487,6 +511,16 @@ 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;
compiler_fence(SeqCst);
self.check_errorsrc()?;
self.check_tx(buffer.len())?;
Ok(())
}
pub async fn write_read(
&mut self,
address: u8,
@ -501,6 +535,22 @@ impl<'d, T: Instance> Twim<'d, T> {
self.check_rx(rd_buffer.len())?;
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,
wr_buffer: &[u8],
rd_buffer: &mut [u8],
) -> Result<(), Error> {
self.setup_write_read_from_ram(address, wr_buffer, rd_buffer, true)?;
self.async_wait().await;
compiler_fence(SeqCst);
self.check_errorsrc()?;
self.check_tx(wr_buffer.len())?;
self.check_rx(rd_buffer.len())?;
Ok(())
}
}
impl<'a, T: Instance> Drop for Twim<'a, T> {
@ -601,11 +651,7 @@ mod eh02 {
bytes: &'w [u8],
buffer: &'w mut [u8],
) -> Result<(), Error> {
if slice_in_ram(bytes) {
self.blocking_write_read(addr, bytes, buffer)
} else {
self.blocking_copy_write_read(addr, bytes, buffer)
}
}
}
}

42
embassy-nrf/src/uarte.rs
View File

@ -22,7 +22,7 @@ use embassy_hal_common::drop::OnDrop;
use embassy_hal_common::unborrow;
use futures::future::poll_fn;
use crate::chip::EASY_DMA_SIZE;
use crate::chip::{EASY_DMA_SIZE, FORCE_COPY_BUFFER_SIZE};
use crate::gpio::sealed::Pin as _;
use crate::gpio::{self, AnyPin, Pin as GpioPin, PselBits};
use crate::interrupt::Interrupt;
@ -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 +226,11 @@ 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
}
pub fn blocking_read(&mut self, buffer: &mut [u8]) -> Result<(), Error> {
self.rx.blocking_read(buffer)
}
@ -231,10 +238,28 @@ impl<'d, T: Instance> Uarte<'d, T> {
pub fn blocking_write(&mut self, buffer: &[u8]) -> Result<(), Error> {
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)
}
}
impl<'d, T: Instance> UarteTx<'d, T> {
pub async fn write(&mut self, buffer: &[u8]) -> Result<(), Error> {
match self.write_from_ram(buffer).await {
Ok(_) => Ok(()),
Err(Error::DMABufferNotInDataMemory) => {
trace!("Copying UARTE tx buffer into RAM for DMA");
let ram_buf = &mut [0; FORCE_COPY_BUFFER_SIZE][..buffer.len()];
ram_buf.copy_from_slice(buffer);
self.write_from_ram(&ram_buf).await
}
Err(error) => Err(error),
}
}
pub async fn write_from_ram(&mut self, buffer: &[u8]) -> Result<(), Error> {
slice_in_ram_or(buffer, Error::DMABufferNotInDataMemory)?;
if buffer.len() == 0 {
return Err(Error::BufferZeroLength);
@ -289,6 +314,19 @@ impl<'d, T: Instance> UarteTx<'d, T> {
}
pub fn blocking_write(&mut self, buffer: &[u8]) -> Result<(), Error> {
match self.blocking_write_from_ram(buffer) {
Ok(_) => Ok(()),
Err(Error::DMABufferNotInDataMemory) => {
trace!("Copying UARTE tx buffer into RAM for DMA");
let ram_buf = &mut [0; FORCE_COPY_BUFFER_SIZE][..buffer.len()];
ram_buf.copy_from_slice(buffer);
self.blocking_write_from_ram(&ram_buf)
}
Err(error) => Err(error),
}
}
pub fn blocking_write_from_ram(&mut self, buffer: &[u8]) -> Result<(), Error> {
slice_in_ram_or(buffer, Error::DMABufferNotInDataMemory)?;
if buffer.len() == 0 {
return Err(Error::BufferZeroLength);

5
embassy-nrf/src/util.rs
View File

@ -19,10 +19,11 @@ pub(crate) fn slice_in_ram<T>(slice: *const [T]) -> bool {
ptr >= SRAM_LOWER && (ptr + len * core::mem::size_of::<T>()) < SRAM_UPPER
}
/// Return an error if slice is not in RAM.
/// Return an error if slice is not in RAM. Skips check if slice is zero-length.
#[cfg(not(feature = "nrf51"))]
pub(crate) fn slice_in_ram_or<T, E>(slice: *const [T], err: E) -> Result<(), E> {
if slice_in_ram(slice) {
let (_, len) = slice_ptr_parts(slice);
if len == 0 || slice_in_ram(slice) {
Ok(())
} else {
Err(err)