diff --git a/src/runtime/src/main.rs b/src/runtime/src/main.rs
index 48522dfa..a202780c 100644
--- a/src/runtime/src/main.rs
+++ b/src/runtime/src/main.rs
@@ -11,6 +11,7 @@ use log::info;
 use libboard_zynq::{timer::GlobalTimer, logger, devc};
 use libsupport_zynq::ram;
 
+mod sd_reader;
 mod proto_core_io;
 mod proto_async;
 mod comms;
diff --git a/src/runtime/src/sd_reader.rs b/src/runtime/src/sd_reader.rs
new file mode 100644
index 00000000..f810405c
--- /dev/null
+++ b/src/runtime/src/sd_reader.rs
@@ -0,0 +1,286 @@
+use core_io::{BufRead, Error, ErrorKind, Read, Result as IoResult, Seek, SeekFrom, Write};
+use fatfs;
+use libboard_zynq::sdio::{sd_card::SdCard, CmdTransferError};
+
+fn cmd_error_to_io_error(_: CmdTransferError) -> Error {
+    Error::new(ErrorKind::Other, "Command transfer error")
+}
+
+const BLOCK_SIZE: usize = 512;
+
+/// SdReader struct implementing `Read + BufRead + Write + Seek` traits for `core_io`.
+/// Used as an adaptor for fatfs crate, but could be used directly for raw data access.
+///
+/// Implementation: all read/writes would be split into unaligned and block-aligned parts,
+/// unaligned read/writes would do a buffered read/write using a block-sized internal buffer,
+/// while aligned transactions would be sent to the SD card directly for performance reason.
+pub struct SdReader<'a> {
+    /// Internal SdCard handle.
+    sd: &'a mut SdCard,
+    /// Read buffer with the size of 1 block.
+    buffer: [u8; BLOCK_SIZE],
+    /// Address for the next byte.
+    byte_addr: u32,
+    /// Internal index for the next byte.
+    /// Normally in range `[0, BLOCK_SIZE - 1]`.
+    ///
+    /// `index = BLOCK_SIZE` means that the `buffer` is invalid for the current `byte_addr`,
+    /// the next `fill_buf` call would fill the buffer.
+    index: usize,
+    /// Dirty flag indicating the content has to be flushed.
+    dirty: bool,
+    /// Base offset for translation from logical address to physical address.
+    offset: u32,
+}
+
+#[derive(Copy, Clone)]
+#[allow(unused)]
+// Partition entry enum, normally we would use entry1.
+pub enum PartitionEntry {
+    Entry1 = 0x1BE,
+    Entry2 = 0x1CE,
+    Entry3 = 0x1DE,
+    Entry4 = 0x1EE,
+}
+
+impl<'a> SdReader<'a> {
+    /// Create SdReader from SdCard
+    pub fn new(sd: &'a mut SdCard) -> SdReader<'a> {
+        SdReader {
+            sd,
+            buffer: [0; BLOCK_SIZE],
+            byte_addr: 0,
+            index: BLOCK_SIZE,
+            dirty: false,
+            offset: 0,
+        }
+    }
+
+    /// Internal read function for unaligned read.
+    /// The read must not cross block boundary.
+    fn read_unaligned(&mut self, buf: &mut [u8]) -> IoResult<usize> {
+        if buf.len() == 0 {
+            return Ok(0);
+        }
+        let filled_buffer = self.fill_buf()?;
+        for (dest, src) in buf.iter_mut().zip(filled_buffer.iter()) {
+            *dest = *src;
+        }
+        self.consume(buf.len());
+        Ok(buf.len())
+    }
+
+    /// Internal write function for unaligned write.
+    /// The write must not cross block boundary.
+    fn write_unaligned(&mut self, buf: &[u8]) -> IoResult<usize> {
+        if buf.len() == 0 {
+            return Ok(0);
+        }
+        // update buffer if needed, as we will flush the entire block later.
+        self.fill_buf()?;
+        self.dirty = true;
+        let dest_buffer = &mut self.buffer[self.index..];
+        for (src, dest) in buf.iter().zip(dest_buffer.iter_mut()) {
+            *dest = *src;
+        }
+        self.consume(buf.len());
+        Ok(buf.len())
+    }
+
+    /// Split the slice into three segments, with the middle block-aligned.
+    /// Alignment depends on the current `self.byte_addr` instead of the slice pointer address
+    fn block_align<'b>(&self, buf: &'b [u8]) -> (&'b [u8], &'b [u8], &'b [u8]) {
+        let head_len = BLOCK_SIZE - (self.byte_addr as usize % BLOCK_SIZE);
+        if head_len > buf.len() {
+            (buf, &[], &[])
+        } else {
+            let remaining_length = buf.len() - head_len;
+            let mid_length = remaining_length - remaining_length % BLOCK_SIZE;
+            let (head, remaining) = buf.split_at(head_len);
+            let (mid, tail) = remaining.split_at(mid_length);
+            (head, mid, tail)
+        }
+    }
+
+    /// Split the mutable slice into three segments, with the middle block-aligned.
+    /// Alignment depends on the current `self.byte_addr` instead of the slice pointer address
+    fn block_align_mut<'b>(&self, buf: &'b mut [u8]) -> (&'b mut [u8], &'b mut [u8], &'b mut [u8]) {
+        let head_len = BLOCK_SIZE - (self.byte_addr as usize % BLOCK_SIZE);
+        if head_len > buf.len() {
+            (buf, &mut [], &mut [])
+        } else {
+            let remaining_length = buf.len() - head_len;
+            let mid_length = remaining_length - remaining_length % BLOCK_SIZE;
+            let (head, remaining) = buf.split_at_mut(head_len);
+            let (mid, tail) = remaining.split_at_mut(mid_length);
+            (head, mid, tail)
+        }
+    }
+
+    /// Invalidate the buffer, so later unaligned read/write would reload the buffer from SD card.
+    fn invalidate_buffer(&mut self) {
+        self.index = BLOCK_SIZE;
+    }
+
+    /// Set the base offset of the SD card, to transform from physical address to logical address.
+    fn set_base_offset(&mut self, offset: u32) -> IoResult<u64> {
+        self.offset = offset;
+        self.seek(SeekFrom::Start(0))
+    }
+
+    /// Mount fatfs from partition entry, and return the fatfs object if success.
+    /// This takes the ownership of self, so currently there is no way to recover from an error,
+    /// except creating a new SD card instance.
+    pub fn mount_fatfs(mut self, entry: PartitionEntry) -> IoResult<fatfs::FileSystem<Self>> {
+        let mut buffer: [u8; 4] = [0; 4];
+        self.seek(SeekFrom::Start(0x1FE))?;
+        self.read_exact(&mut buffer[..2])?;
+        // check MBR signature
+        if buffer[0] != 0x55 || buffer[1] != 0xAA {
+            return Err(Error::new(
+                ErrorKind::InvalidData,
+                "Incorrect signature for MBR sector.",
+            ));
+        }
+        // Read partition ID.
+        self.seek(SeekFrom::Start(entry as u64 + 0x4))?;
+        self.read_exact(&mut buffer[..1])?;
+        match buffer[0] {
+            0x01 | 0x04 | 0x06 | 0x0B => (),
+            _ => {
+                return Err(Error::new(
+                    ErrorKind::InvalidData,
+                    "No FAT partition found for the specified entry.",
+                ))
+            }
+        };
+        // Read LBA
+        self.seek(SeekFrom::Current(0x3))?;
+        self.read_exact(&mut buffer)?;
+        let mut lba: u32 = 0;
+        // Little endian
+        for i in 0..4 {
+            lba |= (buffer[i] as u32) << (i * 8);
+        }
+        // Set to logical address
+        self.set_base_offset(lba * BLOCK_SIZE as u32)?;
+        // setup fatfs
+        fatfs::FileSystem::new(self, fatfs::FsOptions::new())
+    }
+}
+
+impl<'a> Read for SdReader<'a> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<usize> {
+        let total_length = buf.len();
+        let (a, b, c) = self.block_align_mut(buf);
+        self.read_unaligned(a)?;
+        if b.len() > 0 {
+            // invalidate internal buffer
+            self.invalidate_buffer();
+            if let Err(_) = self.sd.read_block(
+                self.byte_addr / BLOCK_SIZE as u32,
+                (b.len() / BLOCK_SIZE) as u16,
+                b,
+            ) {
+                // we have to allow partial read, as per the trait required
+                return Ok(a.len());
+            }
+        }
+        if let Err(_) = self.read_unaligned(c) {
+            // we have to allow partial read, as per the trait required
+            return Ok(a.len() + b.len());
+        }
+        Ok(total_length)
+    }
+}
+
+impl<'a> BufRead for SdReader<'a> {
+    fn fill_buf(&mut self) -> IoResult<&[u8]> {
+        if self.index == BLOCK_SIZE {
+            // flush the buffer if it is dirty before overwriting it with new data
+            if self.dirty {
+                self.flush()?;
+            }
+            // reload buffer
+            self.sd
+                .read_block(self.byte_addr / (BLOCK_SIZE as u32), 1, &mut self.buffer)
+                .map_err(cmd_error_to_io_error)?;
+            self.index = (self.byte_addr as usize) % BLOCK_SIZE;
+        }
+        Ok(&self.buffer[self.index..])
+    }
+
+    fn consume(&mut self, amt: usize) {
+        self.index += amt;
+        self.byte_addr += amt as u32;
+    }
+}
+
+impl<'a> Write for SdReader<'a> {
+    fn write(&mut self, buf: &[u8]) -> IoResult<usize> {
+        let (a, b, c) = self.block_align(buf);
+        self.write_unaligned(a)?;
+        if b.len() > 0 {
+            self.invalidate_buffer();
+            if let Err(_) = self.sd.write_block(
+                self.byte_addr / BLOCK_SIZE as u32,
+                (b.len() / BLOCK_SIZE) as u16,
+                b,
+            ) {
+                return Ok(a.len());
+            }
+        }
+        if let Err(_) = self.write_unaligned(c) {
+            return Ok(a.len() + b.len());
+        }
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> IoResult<()> {
+        if self.dirty {
+            let block_addr = (self.byte_addr - self.index as u32) / (BLOCK_SIZE as u32);
+            self.sd
+                .write_block(block_addr, 1, &self.buffer)
+                .map_err(cmd_error_to_io_error)?;
+            self.dirty = false;
+        }
+        Ok(())
+    }
+}
+
+impl<'a> Seek for SdReader<'a> {
+    fn seek(&mut self, pos: SeekFrom) -> IoResult<u64> {
+        let raw_target = match pos {
+            SeekFrom::Start(x) => self.offset as i64 + x as i64,
+            SeekFrom::Current(x) => self.byte_addr as i64 + x,
+            SeekFrom::End(_) => panic!("SD card does not support seek from end"),
+        };
+        if raw_target < self.offset as i64 || raw_target > core::u32::MAX as i64 {
+            return Err(Error::new(ErrorKind::InvalidInput, "Invalid address"));
+        }
+        let target_byte_addr = raw_target as u32;
+        let address_same_block =
+            self.byte_addr / (BLOCK_SIZE as u32) == target_byte_addr / (BLOCK_SIZE as u32);
+        // if the buffer was invalidated, we consider seek as different block
+        let same_block = address_same_block && self.index != BLOCK_SIZE;
+        if !same_block {
+            self.flush()?;
+        }
+        self.byte_addr = target_byte_addr;
+        self.index = if same_block {
+            target_byte_addr as usize % BLOCK_SIZE
+        } else {
+            // invalidate the buffer as we moved to a different block
+            BLOCK_SIZE
+        };
+        Ok((self.byte_addr - self.offset) as u64)
+    }
+}
+
+impl<'a> Drop for SdReader<'a> {
+    fn drop(&mut self) {
+        // just try to flush it, ignore error if any
+        self.flush().unwrap_or(());
+    }
+}
+