Updated the README and added minor typo fixes

Author: thejpster

README.md

@@ -46,17 +46,25 @@ By default the `VolumeManager` will initialize with a maximum number of `4` open
 let cont: VolumeManager<_, _, 6, 12, 4> = VolumeManager::new_with_limits(block, time_source);
 ```
 
+### Accessing SD Cards using an SD Host Controller
+
+The `SdCard` type requires something that implements `Transport` in order to speak to the SD Card. We supply a generic `SpiTransport` that implements `Transport` using some underlying user-supplied implementation of `embedded_hal::spi::SpiDevice<u8>`. That will work for most applications.
+
+However, if your MCU has a full SD Host Controller peripheral, and if you need high-performance access to your SD Card, you may wish to instead implement `Transport` in a way that uses that peripheral. SD Host Controllers, for example, often support a 4-bit wide interface instead of the 1-bit wide SPI interface, and run at higher clock rates.
+
 ## Supported features
 
-* Open files in all supported methods from an open directory
-* Open an arbitrary number of directories and files
-* Read data from open files
-* Write data to open files
-* Close files
-* Delete files
-* Iterate root directory
-* Iterate sub-directories
-* Log over defmt or the common log interface (feature flags).
+* Talking to SD Cards over SPI (using the `embedded-hal::spi::SpiDevice` trait)
+* Talking to SD Cards over a custom transport (using our `Transport` trait)
+* Opening files in all supported modes from an open directory
+* Opening an arbitrary number of directories and files
+* Reading data from open files
+* Writing data to open files
+* Closing files
+* Deleting files
+* Iterating the root directory
+* Iterating sub-directories
+* Logging over defmt or the common log interface (see feature flags).
 
 ## No-std usage
 

src/lib.rs

@@ -92,10 +92,7 @@ pub use crate::filesystem::{
 use filesystem::DirectoryInfo;
 
 #[doc(inline)]
-pub use crate::sdcard::Error as SdCardError;
-
-#[doc(inline)]
-pub use crate::sdcard::SdCard;
+pub use crate::sdcard::{Error as SdCardError, SdCard, SpiTransport, Transport};
 
 mod volume_mgr;
 #[doc(inline)]

src/sdcard/mod.rs

@@ -5,6 +5,8 @@
 
 pub mod proto;
 mod spi;
+
+#[doc(inline)]
 pub use spi::SpiTransport;
 
 use crate::{Block, BlockCount, BlockDevice, BlockIdx};
@@ -20,18 +22,7 @@ use crate::debug;
 // Types and Implementations
 // ****************************************************************************
 
-/// Driver for an SD Card on an SPI bus.
-///
-/// Built from an [`SpiDevice`] implementation and a Chip Select pin.
-///
-/// Before talking to the SD Card, the caller needs to send 74 clocks cycles on
-/// the SPI Clock line, at 400 kHz, with no chip-select asserted (or at least,
-/// not the chip-select of the SD Card).
-///
-/// This kind of breaks the embedded-hal model, so how to do this is left to
-/// the caller. You could drive the SpiBus directly, or use an SpiDevice with
-/// a dummy chip-select pin. Or you could try just not doing the 74 clocks and
-/// see if your card works anyway - some do, some don't.
+/// Driver for an SD Card using some generic SD Card [`Transport`].
 ///
 /// All the APIs take `&self` - mutability is handled using an inner `RefCell`.
 ///
@@ -56,6 +47,12 @@ where
 {
     /// Create a new SD/MMC Card driver using a raw SPI interface.
     ///
+    /// This is just a short-cut method to provide backwards compatibility with
+    /// our old API.
+    ///
+    /// It creates an [`SpiTransport`] for you, so refer to the documentation
+    /// there for important details.
+    ///
     /// The card will not be initialised at this time. Initialisation is
     /// deferred until a method is called on the object.
     ///
@@ -64,10 +61,14 @@ where
         Self::new_spi_with_options(spi, delayer, AcquireOpts::default())
     }
 
-    /// Construct a new SD/MMC Card driver, using a raw SPI interface and the given options.
+    /// Construct a new SD/MMC Card driver, using a raw SPI interface and the
+    /// given options.
     ///
-    /// See the docs of the [`SdCard`] struct for more information about
-    /// how to construct the needed `SPI` and `CS` types.
+    /// This is just a short-cut method to provide backwards compatibility with
+    /// our old API.
+    ///
+    /// It creates an [`SpiTransport`] for you, so refer to the documentation
+    /// there for important details.
     ///
     /// The card will not be initialised at this time. Initialisation is
     /// deferred until a method is called on the object.
@@ -184,7 +185,11 @@ impl<T: Transport> BlockDevice for SdCard<T> {
     }
 }
 
-/// Abstract SD card transportation interface.
+/// Abstract SD Card Transport interface.
+///
+/// We implement this trait to produce an SPI based transport over in
+/// [`SpiTransport`]. You can implement it yourself to support your favourite SD
+/// Host Controller if you prefer.
 pub trait Transport {
     /// Read one or more blocks, starting at the given block index.
     fn read(&mut self, blocks: &mut [Block], start_block_idx: BlockIdx) -> Result<(), Error>;

src/sdcard/spi.rs

@@ -1,4 +1,4 @@
-//! Implements the BlockDevice trait for an SD/MMC Protocol over SPI.
+//! Implements the [`Transport`] trait for speaking SD/MMC Protocol over SPI.
 //!
 //! This is currently optimised for readability and debugability, not
 //! performance.
@@ -7,9 +7,9 @@ use super::{proto::*, AcquireOpts, CardType, Delay, Error};
 use crate::blockdevice::{Block, BlockCount, BlockIdx};
 use crate::{debug, trace, warn};
 
-/// SPI transportation for the SD Card driver.
+/// An SPI-based implementation of [`Transport`](crate::Transport).
 ///
-/// All the APIs required `&mut self`.
+/// All the APIs require `&mut self`.
 pub struct SpiTransport<SPI, DELAYER>
 where
     SPI: embedded_hal::spi::SpiDevice<u8>,
@@ -27,6 +27,15 @@ where
     DELAYER: embedded_hal::delay::DelayNs,
 {
     /// Construct a new raw SPI transport interface for SD/MMC Card.
+    ///
+    /// Before talking to the SD Card, the caller needs to send 74 clocks cycles
+    /// on the SPI Clock line, at 400 kHz, with no chip-select asserted (or at
+    /// least, not the chip-select of the SD Card).
+    ///
+    /// This kind of breaks the embedded-hal model, so how to do this is left to
+    /// the caller. You could drive the SpiBus directly, or use an SpiDevice
+    /// with a dummy chip-select pin. Or you could try just not doing the 74
+    /// clocks and see if your card works anyway - some do, some don't.
     pub fn new(spi: SPI, delayer: DELAYER, options: AcquireOpts) -> Self {
         SpiTransport {
             spi,