Introduce SDMMC write_blocks

`write_block` needs to be called for every 512 bytes long block that is
to be written to the SD card. Each of these calls requires the overhead
of negotiating the write command.

With this patch, `write_blocks` is introduced, mirroring the behavior
of `read_block` and `read_blocks`. This new method helped me to improve
write speed of the original 9492 kB/s to 66252 kB/s.

Signed-off-by: Petr Horacek <petr@zlosynth.com>

CHANGELOG.md

@@ -7,7 +7,8 @@
 * Update `smoltcp` dependency to `0.9.0`
 * MSRV increased to 1.65.0
 * add `IntoAf` trait to restrict `into_alternate` [#346]
-* sdmmc: Fix read speed test.
+* sdmmc: Introduce `write_blocks`
+* sdmmc: Fix read speed test
 
 ## [v0.14.0] 2023-03-22
 

examples/sdmmc.rs

@@ -159,14 +159,10 @@ fn main() -> ! {
  info!("Read 10 blocks at {} bytes/s", 5120. / duration);
  info!("");
 
- let write_buffer = [0x34; 512];
+ let write_buffer = [0x34; 512 * 10];
  let start = pac::DWT::cycle_count();
 
- for i in 0..10 {
- if let Err(err) = sdmmc.write_block(i, &write_buffer) {
- info!("Failed to write block {}: {:?}", i, err);
- }
- }
+ sdmmc.write_blocks(0, &write_buffer).unwrap();
 
  let end = pac::DWT::cycle_count();
  let duration = (end - start) as f32 / ccdr.clocks.c_ck().raw() as f32;

src/sdmmc.rs

@@ -739,20 +739,24 @@ macro_rules! sdmmc {
  }
 
  /// Write block to card. Buffer must be 512 bytes
- pub fn write_block(
+ pub fn write_blocks(
  &mut self,
  address: u32,
- buffer: &[u8; 512]
+ buffer: &[u8]
  ) -> Result<(), Error> {
  let _card = self.card()?;
 
+ assert!(buffer.len() % 512 == 0,
+ "Buffer length must be a multiple of 512");
+ let n_blocks = buffer.len() / 512;
+
  if !self.cmd16_illegal {
  self.cmd(common_cmd::set_block_length(512))?; // CMD16
  }
 
  // Setup write command
- self.start_datapath_transfer(512, 9, Dir::HostToCard);
- self.cmd(common_cmd::write_single_block(address))?; // CMD24
+ self.start_datapath_transfer(512 * n_blocks as u32, 9, Dir::HostToCard);
+ self.cmd(common_cmd::write_multiple_blocks(address))?; // CMD25
 
  let mut i = 0;
  let mut status;
@@ -778,6 +782,8 @@ macro_rules! sdmmc {
  }
  }
 
+ self.cmd(common_cmd::stop_transmission())?; // CMD12
+
  err_from_datapath_sm!(status);
  self.clear_static_interrupt_flags();