Read volume label from SD

Cargo.lock

@@ -490,6 +490,7 @@ name = "embassy-rp-skeleton"
 version = "0.1.0"
 dependencies = [
  "byte-slice-cast 1.2.2",
+ "byteorder",
  "cortex-m",
  "cortex-m-rt",
  "critical-section",

Cargo.toml

@@ -49,5 +49,9 @@ pio = "0.2.1"
 rand = { version = "0.8.5", default-features = false }
 embedded-sdmmc = "0.7.0"
 
+# Dependencies of embedded-sdmmc that I need to use directly
+byteorder = {version = "1", default-features = false}
+
+
 [profile.release]
 debug = 2

src/main.rs

@@ -6,6 +6,7 @@
 #![no_std]
 #![no_main]
 
+use byteorder::ByteOrder;
 use defmt::*;
 use embassy_embedded_hal::SetConfig;
 use embassy_executor::Spawner;
@@ -13,6 +14,7 @@ use embassy_rp::spi::Spi;
 use embassy_rp::{gpio, spi};
 use embedded_hal_bus::spi::ExclusiveDevice;
 use embedded_sdmmc::sdcard::{DummyCsPin, SdCard};
+use embedded_sdmmc::{Block, BlockCount, BlockDevice, BlockIdx, FatVolume, VolumeIdx, VolumeType};
 use gpio::{Level, Output};
 use {defmt_rtt as _, panic_probe as _};
 
@@ -52,21 +54,27 @@ async fn main(_spawner: Spawner) {
     let mut config = spi::Config::default();
     config.frequency = 16_000_000;
     sdcard.spi(|dev| dev.bus_mut().set_config(&config)).ok();
-    info!("here");
 
     // Now let's look for volumes (also known as partitions) on our block device.
     // To do this we need a Volume Manager. It will take ownership of the block device.
     let mut volume_mgr = embedded_sdmmc::VolumeManager::new(sdcard, DummyTimesource());
-    info!("here");
+    {
+        let device = volume_mgr.device();
+        let info = read_volume_info(device, VolumeIdx(0)).unwrap();
+        info!("Volume 0: name: {:?}", defmt::Debug2Format(&info));
+    }
 
     // Try and access Volume 0 (i.e. the first partition).
     // The volume object holds information about the filesystem on that volume.
-    let mut volume0 = volume_mgr.open_volume(embedded_sdmmc::VolumeIdx(0)).unwrap();
+    let mut volume0 = volume_mgr
+        .open_volume(embedded_sdmmc::VolumeIdx(0))
+        .unwrap();
     info!("Volume 0: {:?}", defmt::Debug2Format(&volume0));
 
     // Open the root directory (mutably borrows from the volume).
     let mut root_dir = volume0.open_root_dir().unwrap();
 
+    {
         // Open a file called "MY_FILE.TXT" in the root directory
         // This mutably borrows the directory.
         let mut my_file = root_dir
@@ -80,7 +88,95 @@ async fn main(_spawner: Spawner) {
                 info!("{:a}", buf[..n]);
             }
         }
+    }
+    {
+        let mut my_file = root_dir
+            .open_file_in_dir("MY_FILE.TXT", embedded_sdmmc::Mode::ReadWriteAppend)
+            .unwrap();
 
-    loop {}
+        my_file.write(b"Another one\n").unwrap();
     }
 
+    info!("Program end")
+}
+
+pub fn read_volume_info<D>(
+    block_device: &mut D,
+    volume_idx: VolumeIdx,
+) -> Result<FatVolume, embedded_sdmmc::Error<D::Error>>
+where
+    D: BlockDevice,
+{
+    use byteorder::LittleEndian;
+    use embedded_sdmmc::Error;
+    const PARTITION1_START: usize = 446;
+    const PARTITION2_START: usize = PARTITION1_START + PARTITION_INFO_LENGTH;
+    const PARTITION3_START: usize = PARTITION2_START + PARTITION_INFO_LENGTH;
+    const PARTITION4_START: usize = PARTITION3_START + PARTITION_INFO_LENGTH;
+    const FOOTER_START: usize = 510;
+    const FOOTER_VALUE: u16 = 0xAA55;
+    const PARTITION_INFO_LENGTH: usize = 16;
+    const PARTITION_INFO_STATUS_INDEX: usize = 0;
+    const PARTITION_INFO_TYPE_INDEX: usize = 4;
+    const PARTITION_INFO_LBA_START_INDEX: usize = 8;
+    const PARTITION_INFO_NUM_BLOCKS_INDEX: usize = 12;
+    /// Marker for a FAT32 partition. Sometimes also use for FAT16 formatted
+    /// partitions.
+    const PARTITION_ID_FAT32_LBA: u8 = 0x0C;
+    /// Marker for a FAT16 partition with LBA. Seen on a Raspberry Pi SD card.
+    const PARTITION_ID_FAT16_LBA: u8 = 0x0E;
+    /// Marker for a FAT16 partition. Seen on a card formatted with the official
+    /// SD-Card formatter.
+    const PARTITION_ID_FAT16: u8 = 0x06;
+    /// Marker for a FAT32 partition. What Macosx disk utility (and also SD-Card formatter?)
+    /// use.
+    const PARTITION_ID_FAT32_CHS_LBA: u8 = 0x0B;
+
+    let (part_type, lba_start, num_blocks) = {
+        let mut blocks = [Block::new()];
+        block_device
+            .read(&mut blocks, BlockIdx(0), "read_mbr")
+            .map_err(Error::DeviceError)?;
+        let block = &blocks[0];
+        // We only support Master Boot Record (MBR) partitioned cards, not
+        // GUID Partition Table (GPT)
+        if LittleEndian::read_u16(&block[FOOTER_START..FOOTER_START + 2]) != FOOTER_VALUE {
+            return Err(Error::FormatError("Invalid MBR signature"));
+        }
+        let partition = match volume_idx {
+            VolumeIdx(0) => &block[PARTITION1_START..(PARTITION1_START + PARTITION_INFO_LENGTH)],
+            VolumeIdx(1) => &block[PARTITION2_START..(PARTITION2_START + PARTITION_INFO_LENGTH)],
+            VolumeIdx(2) => &block[PARTITION3_START..(PARTITION3_START + PARTITION_INFO_LENGTH)],
+            VolumeIdx(3) => &block[PARTITION4_START..(PARTITION4_START + PARTITION_INFO_LENGTH)],
+            _ => {
+                return Err(Error::NoSuchVolume);
+            }
+        };
+        // Only 0x80 and 0x00 are valid (bootable, and non-bootable)
+        if (partition[PARTITION_INFO_STATUS_INDEX] & 0x7F) != 0x00 {
+            return Err(Error::FormatError("Invalid partition status"));
+        }
+        let lba_start = LittleEndian::read_u32(
+            &partition[PARTITION_INFO_LBA_START_INDEX..(PARTITION_INFO_LBA_START_INDEX + 4)],
+        );
+        let num_blocks = LittleEndian::read_u32(
+            &partition[PARTITION_INFO_NUM_BLOCKS_INDEX..(PARTITION_INFO_NUM_BLOCKS_INDEX + 4)],
+        );
+        (
+            partition[PARTITION_INFO_TYPE_INDEX],
+            BlockIdx(lba_start),
+            BlockCount(num_blocks),
+        )
+    };
+    match part_type {
+        PARTITION_ID_FAT32_CHS_LBA
+        | PARTITION_ID_FAT32_LBA
+        | PARTITION_ID_FAT16_LBA
+        | PARTITION_ID_FAT16 => {
+            let volume = embedded_sdmmc::fat::parse_volume(block_device, lba_start, num_blocks)?;
+            let VolumeType::Fat(fat) = volume;
+            Ok(fat)
+        }
+        _ => Err(Error::FormatError("Partition type not supported")),
+    }
+}