Optimize SDMMC FAT writting speeds

With this patch, the FAT write binding would use sdmmc CMD25 to write
large blocks of data.

Signed-off-by: Petr Horacek <[email protected]>

CHANGELOG.md

@@ -8,6 +8,7 @@
 * MSRV increased to 1.65.0
 * add `IntoAf` trait to restrict `into_alternate` [#346]
 * sdmmc: Introduce `write_blocks` [#453]
+* sdmmc-fat: Optimize writing speeds [#456]
 
 ## [v0.14.0] 2023-03-22
 

examples/sdmmc_fat.rs

@@ -2,7 +2,7 @@
 #![no_std]
 
 use {
-    embedded_sdmmc::{Controller, VolumeIdx},
+    embedded_sdmmc::{Controller, Mode, VolumeIdx},
     stm32h7xx_hal::sdmmc::{SdCard, Sdmmc},
     stm32h7xx_hal::{pac, prelude::*, rcc},
 };
@@ -89,14 +89,55 @@ unsafe fn main() -> ! {
     // See https://github.com/rust-embedded-community/embedded-sdmmc-rs for docs
     // and more examples
 
+    log::info!("Initialize file system manager");
     let mut sd_fatfs = Controller::new(sd.sdmmc_block_device(), TimeSource);
-    let sd_fatfs_volume = sd_fatfs.get_volume(VolumeIdx(0)).unwrap();
+    let mut sd_fatfs_volume = sd_fatfs.get_volume(VolumeIdx(0)).unwrap();
     let sd_fatfs_root_dir = sd_fatfs.open_root_dir(&sd_fatfs_volume).unwrap();
+
+    log::info!("List all the directories and their info");
     sd_fatfs
         .iterate_dir(&sd_fatfs_volume, &sd_fatfs_root_dir, |entry| {
             log::info!("{:?}", entry);
         })
         .unwrap();
+
+    const WRITE_BUFFER: [u8; 8 * 1024] = [b'B'; 8 * 1024];
+
+    for (filename, length) in
+        &[("small.txt", 8), ("big.txt", WRITE_BUFFER.len())]
+    {
+        log::info!("Open file {:?}", filename);
+        let mut file = sd_fatfs
+            .open_file_in_dir(
+                &mut sd_fatfs_volume,
+                &sd_fatfs_root_dir,
+                filename,
+                Mode::ReadWriteCreateOrTruncate,
+            )
+            .unwrap();
+
+        log::info!("Write {:?} characters in it", length);
+        sd_fatfs
+            .write(&mut sd_fatfs_volume, &mut file, &WRITE_BUFFER[0..*length])
+            .unwrap();
+
+        log::info!("Read it back and confirm it contains the expected content");
+        file.seek_from_start(0).unwrap();
+        while !file.eof() {
+            let mut buffer = [0u8; 1024];
+            let num_read = sd_fatfs
+                .read(&sd_fatfs_volume, &mut file, &mut buffer)
+                .unwrap();
+            for b in &buffer[0..num_read] {
+                assert_eq!(*b as char, 'B');
+            }
+        }
+
+        sd_fatfs.close_file(&sd_fatfs_volume, file).unwrap();
+    }
+
+    log::info!("Test successfully finished");
+
     sd_fatfs.close_dir(&sd_fatfs_volume, sd_fatfs_root_dir);
 
     loop {

src/sdmmc.rs

@@ -804,12 +804,23 @@ macro_rules! sdmmc {
                     &mut self,
                     address: u32,
                     buffer: &[u8]
+                ) -> Result<(), Error> {
+                    self.write_blocks_begin(address, buffer.len())?;
+                    self.write_blocks_feed(buffer);
+                    self.write_blocks_conclude()?;
+                    Ok(())
+                }
+
+                fn write_blocks_begin(
+                    &mut self,
+                    address: u32,
+                    buffer_len: usize,
                 ) -> Result<(), Error> {
                     let _card = self.card()?;
 
-                    assert!(buffer.len() % 512 == 0,
+                    assert!(buffer_len % 512 == 0,
                             "Buffer length must be a multiple of 512");
-                    let n_blocks = buffer.len() / 512;
+                    let n_blocks = buffer_len / 512;
 
                     if !self.cmd16_illegal {
                         self.cmd(common_cmd::set_block_length(512))?; // CMD16
@@ -819,6 +830,10 @@ macro_rules! sdmmc {
                     self.start_datapath_transfer(512 * n_blocks as u32, 9, Dir::HostToCard);
                     self.cmd(common_cmd::write_multiple_blocks(address))?; // CMD25
 
+                    Ok(())
+                }
+
+                fn write_blocks_feed(&mut self, buffer: &[u8]) {
                     let mut i = 0;
                     let mut status;
                     while {
@@ -842,6 +857,10 @@ macro_rules! sdmmc {
                             break
                         }
                     }
+                }
+
+                fn write_blocks_conclude(&mut self) -> Result<(), Error> {
+                    let mut status;
 
                     while {
                         status = self.sdmmc.star.read();
@@ -850,6 +869,7 @@ macro_rules! sdmmc {
                           || status.dtimeout().bit()
                           || status.dataend().bit())
                     } {}
+
                     self.cmd(common_cmd::stop_transmission())?; // CMD12
 
                     err_from_datapath_sm!(status);
@@ -1339,10 +1359,17 @@ macro_rules! sdmmc {
                     blocks: &[embedded_sdmmc::Block],
                     start_block_idx: embedded_sdmmc::BlockIdx,
                 ) -> Result<(), Self::Error> {
-                    let start = start_block_idx.0;
                     let mut sdmmc = self.sdmmc.borrow_mut();
-                    for block_idx in start..(start + blocks.len() as u32) {
-                        sdmmc.write_block(block_idx, &blocks[(block_idx - start) as usize].contents)?;
+                    let start = start_block_idx.0;
+                    if blocks.len() == 1 {
+                        sdmmc.write_block(start, &blocks[0].contents)?;
+                    } else {
+                        let total_length = embedded_sdmmc::Block::LEN * blocks.len();
+                        sdmmc.write_blocks_begin(start, total_length)?;
+                        for block in blocks.iter() {
+                            sdmmc.write_blocks_feed(&block.contents);
+                        }
+                        sdmmc.write_blocks_conclude()?;
                     }
                     Ok(())
                 }