diff --git a/drivers/sdcard/sdcard.py b/drivers/sdcard/sdcard.py
new file mode 100644
index 000000000..e51a594d8
--- /dev/null
+++ b/drivers/sdcard/sdcard.py
@@ -0,0 +1,202 @@
+"""
+Micro Python driver for SD cards using SPI bus.
+
+Requires an SPI bus and a CS pin.  Provides readblocks and writeblocks
+methods so the device can be mounted as a filesystem.
+
+Example usage:
+
+    import pyb, sdcard, os
+    sd = sdcard.SDCard(pyb.SPI(1), pyb.Pin.board.X5)
+    pyb.mount(sd, '/sd2')
+    os.listdir('/')
+
+"""
+
+import pyb
+
+class SDCard:
+    CMD_TIMEOUT = const(100)
+
+    R1_IDLE_STATE = const(1 << 0)
+    #R1_ERASE_RESET = const(1 << 1)
+    R1_ILLEGAL_COMMAND = const(1 << 2)
+    #R1_COM_CRC_ERROR = const(1 << 3)
+    #R1_ERASE_SEQUENCE_ERROR = const(1 << 4)
+    #R1_ADDRESS_ERROR = const(1 << 5)
+    #R1_PARAMETER_ERROR = const(1 << 6)
+
+    def __init__(self, spi, cs):
+        self.spi = spi
+        self.cs = cs
+
+        self.cmdbuf = bytearray(6)
+        self.dummybuf = bytearray(512)
+        for i in range(512):
+            self.dummybuf[i] = 0xff
+        self.dummybuf_memoryview = memoryview(self.dummybuf)
+
+        # initialise the card
+        self.init_card()
+
+    def init_card(self):
+        # init CS pin
+        self.cs.high()
+        self.cs.init(self.cs.OUT_PP)
+
+        # init SPI bus; use low data rate for initialisation
+        self.spi.init(self.spi.MASTER, baudrate=100000, phase=0, polarity=0)
+
+        # clock card at least 100 cycles with cs high
+        for i in range(16):
+            self.spi.send(0xff)
+
+        # CMD0: init card; should return R1_IDLE_STATE (allow 2 attempts)
+        if self.cmd(0, 0, 0x95) != R1_IDLE_STATE:
+            if self.cmd(0, 0, 0x95) != R1_IDLE_STATE:
+                raise OSError("no SD card")
+
+        # CMD8: determine card version
+        r = self.cmd(8, 0x01aa, 0x87, 4)
+        if r == R1_IDLE_STATE:
+            self.init_card_v2()
+        elif r == (R1_IDLE_STATE | R1_ILLEGAL_COMMAND):
+            self.init_card_v1()
+        else:
+            raise OSError("couldn't determine SD card version")
+
+        # get the number of sectors
+        # CMD9: response R2 (R1 byte + 16-byte block read)
+        if self.cmd(9, 0, 0, 0, False) != 0:
+            raise OSError("no response from SD card")
+        csd = bytearray(16)
+        self.readinto(csd)
+        if csd[0] & 0xc0 != 0x40:
+            raise OSError("SD card CSD format not supported")
+        self.sectors = ((csd[8] << 8 | csd[9]) + 1) * 2014
+        #print('sectors', self.sectors)
+
+        # CMD16: set block length to 512 bytes
+        if self.cmd(16, 512, 0) != 0:
+            raise OSError("can't set 512 block size")
+
+        # set to high data rate now that it's initialised
+        self.spi.init(self.spi.MASTER, baudrate=1320000, phase=0, polarity=0)
+
+    def init_card_v1(self):
+        for i in range(CMD_TIMEOUT):
+            self.cmd(55, 0, 0)
+            if self.cmd(41, 0, 0) == 0:
+                self.cdv = 512
+                #print("[SDCard] v1 card")
+                return
+        raise OSError("timeout waiting for v1 card")
+
+    def init_card_v2(self):
+        for i in range(CMD_TIMEOUT):
+            pyb.delay(50)
+            self.cmd(58, 0, 0, 4)
+            self.cmd(55, 0, 0)
+            if self.cmd(41, 0x40000000, 0) == 0:
+                self.cmd(58, 0, 0, 4)
+                self.cdv = 1
+                #print("[SDCard] v2 card")
+                return
+        raise OSError("timeout waiting for v2 card")
+
+    def cmd(self, cmd, arg, crc, final=0, release=True):
+        self.cs.low()
+
+        # create and send the command
+        buf = self.cmdbuf
+        buf[0] = 0x40 | cmd
+        buf[1] = arg >> 24
+        buf[2] = arg >> 16
+        buf[3] = arg >> 8
+        buf[4] = arg
+        buf[5] = crc
+        self.spi.send(buf)
+
+        # wait for the repsonse (response[7] == 0)
+        for i in range(CMD_TIMEOUT):
+            response = self.spi.send_recv(0xff)[0]
+            if not (response & 0x80):
+                # this could be a big-endian integer that we are getting here
+                for j in range(final):
+                    self.spi.send(0xff)
+                if release:
+                    self.cs.high()
+                    self.spi.send(0xff)
+                return response
+
+        # timeout
+        self.cs.high()
+        self.spi.send(0xff)
+        return -1
+
+    def readinto(self, buf):
+        self.cs.low()
+
+        # read until start byte (0xff)
+        while self.spi.send_recv(0xff)[0] != 0xfe:
+            pass
+
+        # read data
+        mv = self.dummybuf_memoryview[:len(buf)]
+        self.spi.send_recv(mv, recv=buf)
+
+        # read checksum
+        self.spi.send(0xff)
+        self.spi.send(0xff)
+
+        self.cs.high()
+        self.spi.send(0xff)
+
+    def write(self, buf):
+        self.cs.low()
+
+        # send: start of block, data, checksum
+        self.spi.send(0xfe)
+        self.spi.send(buf)
+        self.spi.send(0xff)
+        self.spi.send(0xff)
+
+        # check the response
+        if (self.spi.send_recv(0xff)[0] & 0x1f) != 0x05:
+            self.cs.high()
+            self.spi.send(0xff)
+            return
+
+        # wait for write to finish
+        while self.spi.send_recv(0xff)[0] == 0:
+            pass
+
+        self.cs.high()
+        self.spi.send(0xff)
+
+    def count(self):
+        return self.sectors
+
+    def readblocks(self, block_num, buf):
+        # TODO support multiple block reads
+        assert len(buf) == 512
+
+        # CMD17: set read address for single block
+        if self.cmd(17, block_num * self.cdv, 0) != 0:
+            return 1
+
+        # receive the data
+        self.readinto(buf)
+        return 0
+
+    def writeblocks(self, block_num, buf):
+        # TODO support multiple block writes
+        assert len(buf) == 512
+
+        # CMD24: set write address for single block
+        if self.cmd(24, block_num * self.cdv, 0) != 0:
+            return 1
+
+        # send the data
+        self.write(buf)
+        return 0