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sdcard: Compute CRC7 for all SPI commands. #1088

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d04161a
sdcard: Compute CRC7 for all SPI commands.
kwagyeman Feb 25, 2026
95f72a7
sdcard: Add read/write speed test to sdtest.
kwagyeman Feb 25, 2026
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43 changes: 26 additions & 17 deletions micropython/drivers/storage/sdcard/sdcard.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,15 @@
_TOKEN_DATA = const(0xFE)


def _crc7(buf, n):
crc = 0
for i in range(n):
crc ^= buf[i]
for j in range(8):
crc = ((crc << 1) ^ (0x12 * (crc >> 7))) & 0xFF
return crc | 1


class SDCard:
def __init__(self, spi, cs, baudrate=1320000):
self.spi = spi
Expand Down Expand Up @@ -76,13 +85,13 @@ def init_card(self, baudrate):

# CMD0: init card; should return _R1_IDLE_STATE (allow 5 attempts)
for _ in range(5):
if self.cmd(0, 0, 0x95) == _R1_IDLE_STATE:
if self.cmd(0, 0) == _R1_IDLE_STATE:
break
else:
raise OSError("no SD card")

# CMD8: determine card version
r = self.cmd(8, 0x01AA, 0x87, 4)
r = self.cmd(8, 0x01AA, 4)
if r == _R1_IDLE_STATE:
self.init_card_v2()
elif r == (_R1_IDLE_STATE | _R1_ILLEGAL_COMMAND):
Expand All @@ -92,7 +101,7 @@ def init_card(self, baudrate):

# get the number of sectors
# CMD9: response R2 (R1 byte + 16-byte block read)
if self.cmd(9, 0, 0, 0, False) != 0:
if self.cmd(9, 0, 0, False) != 0:
raise OSError("no response from SD card")
csd = bytearray(16)
self.readinto(csd)
Expand All @@ -109,7 +118,7 @@ def init_card(self, baudrate):
# print('sectors', self.sectors)

# CMD16: set block length to 512 bytes
if self.cmd(16, 512, 0) != 0:
if self.cmd(16, 512) != 0:
raise OSError("can't set 512 block size")

# set to high data rate now that it's initialised
Expand All @@ -118,8 +127,8 @@ def init_card(self, baudrate):
def init_card_v1(self):
for i in range(_CMD_TIMEOUT):
time.sleep_ms(50)
self.cmd(55, 0, 0)
if self.cmd(41, 0, 0) == 0:
self.cmd(55, 0)
if self.cmd(41, 0) == 0:
# SDSC card, uses byte addressing in read/write/erase commands
self.cdv = 512
# print("[SDCard] v1 card")
Expand All @@ -129,10 +138,10 @@ def init_card_v1(self):
def init_card_v2(self):
for i in range(_CMD_TIMEOUT):
time.sleep_ms(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) # 4-byte response, negative means keep the first byte
self.cmd(58, 0, 4)
self.cmd(55, 0)
if self.cmd(41, 0x40000000) == 0:
self.cmd(58, 0, -4) # 4-byte response, negative means keep the first byte
ocr = self.tokenbuf[0] # get first byte of response, which is OCR
if not ocr & 0x40:
# SDSC card, uses byte addressing in read/write/erase commands
Expand All @@ -144,7 +153,7 @@ def init_card_v2(self):
return
raise OSError("timeout waiting for v2 card")

def cmd(self, cmd, arg, crc, final=0, release=True, skip1=False):
def cmd(self, cmd, arg, final=0, release=True, skip1=False):
self.cs(0)

# create and send the command
Expand All @@ -154,7 +163,7 @@ def cmd(self, cmd, arg, crc, final=0, release=True, skip1=False):
buf[2] = arg >> 16
buf[3] = arg >> 8
buf[4] = arg
buf[5] = crc
buf[5] = _crc7(buf, 5)
self.spi.write(buf)

if skip1:
Expand Down Expand Up @@ -250,15 +259,15 @@ def readblocks(self, block_num, buf):
assert nblocks and not len(buf) % 512, "Buffer length is invalid"
if nblocks == 1:
# CMD17: set read address for single block
if self.cmd(17, block_num * self.cdv, 0, release=False) != 0:
if self.cmd(17, block_num * self.cdv, release=False) != 0:
# release the card
self.cs(1)
raise OSError(5) # EIO
# receive the data and release card
self.readinto(buf)
else:
# CMD18: set read address for multiple blocks
if self.cmd(18, block_num * self.cdv, 0, release=False) != 0:
if self.cmd(18, block_num * self.cdv, release=False) != 0:
# release the card
self.cs(1)
raise OSError(5) # EIO
Expand All @@ -269,7 +278,7 @@ def readblocks(self, block_num, buf):
self.readinto(mv[offset : offset + 512])
offset += 512
nblocks -= 1
if self.cmd(12, 0, 0xFF, skip1=True):
if self.cmd(12, 0, skip1=True):
raise OSError(5) # EIO

def writeblocks(self, block_num, buf):
Expand All @@ -281,14 +290,14 @@ def writeblocks(self, block_num, buf):
assert nblocks and not err, "Buffer length is invalid"
if nblocks == 1:
# CMD24: set write address for single block
if self.cmd(24, block_num * self.cdv, 0) != 0:
if self.cmd(24, block_num * self.cdv) != 0:
raise OSError(5) # EIO

# send the data
self.write(_TOKEN_DATA, buf)
else:
# CMD25: set write address for first block
if self.cmd(25, block_num * self.cdv, 0) != 0:
if self.cmd(25, block_num * self.cdv) != 0:
raise OSError(5) # EIO
# send the data
offset = 0
Expand Down
21 changes: 21 additions & 0 deletions micropython/drivers/storage/sdcard/sdtest.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
# Peter hinch 30th Jan 2016
import machine
import os
import time
import sdcard


Expand Down Expand Up @@ -44,6 +45,26 @@ def sdtest():
result2 = f.read()
print(len(result2), "bytes read")

fn = "/fc/speed.bin"
buf = bytearray(32768) # 32 KB buffer

print()
print("Write speed test")
t = time.ticks_ms()
with open(fn, "wb") as f:
for _ in range(32): # 1 MB total
f.write(buf)
elapsed = time.ticks_diff(time.ticks_ms(), t)
print("{} KB/s".format(32768 * 32 // elapsed))

print("Read speed test")
t = time.ticks_ms()
with open(fn, "rb") as f:
while f.readinto(buf):
pass
elapsed = time.ticks_diff(time.ticks_ms(), t)
print("{} KB/s".format(32768 * 32 // elapsed))

os.umount("/fc")

print()
Expand Down
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