circuitpython/drivers/sdcard/sdcard.py

"""
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 5 attempts)
        for _ in range(5):
            if self.cmd(0, 0, 0x95) == R1_IDLE_STATE:
                break
        else:
            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