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drivers/sdcard: Do not release CS during the middle of read operations. 

It seems that some cards do not tolerate releasing the card (by setting CS
high) after issuing CMD17 (and 18) and raising it again before reading
data. Somehow this causes the 0xfe data start marker not being read and
SDCard.readinto() is spinning forever (or until this byte is in the data).

This seems to fix weird behviour of SDCard.readblocks() returning different
data, also solved hanging os.mount() for my case with a 16GB Infineon card.

This stackexchange answer gives more context:
https://electronics.stackexchange.com/questions/307214/sd-card-spi-interface-issue-read-operation-returns-0x3f-0xff-instead-of-0x7f-0#307268
This commit is contained in:
Mateusz Kijowski 2018-06-29 01:32:02 +02:00 committed by Damien George
parent 14ab81e87a
commit 1751f5ac7b
1 changed files with 9 additions and 4 deletions
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13
drivers/sdcard/sdcard.py
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@ -174,7 +174,7 @@ class SDCard:
# read until start byte (0xff) # read until start byte (0xff)
while True: while True:
self.spi.readinto(self.tokenbuf, 0xff) self.spi.readinto(self.tokenbuf, 0xff)
if self.tokenbuf[0] == 0xfe: if self.tokenbuf[0] == _TOKEN_DATA:
break break
# read data # read data
@ -228,17 +228,22 @@ class SDCard:
assert nblocks and not len(buf) % 512, 'Buffer length is invalid' assert nblocks and not len(buf) % 512, 'Buffer length is invalid'
if nblocks == 1: if nblocks == 1:
# CMD17: set read address for single block # CMD17: set read address for single block
if self.cmd(17, block_num * self.cdv, 0) != 0: if self.cmd(17, block_num * self.cdv, 0, release=False) != 0:
# release the card
self.cs(1)
raise OSError(5) # EIO raise OSError(5) # EIO
# receive the data # receive the data and release card
self.readinto(buf) self.readinto(buf)
else: else:
# CMD18: set read address for multiple blocks # CMD18: set read address for multiple blocks
if self.cmd(18, block_num * self.cdv, 0) != 0: if self.cmd(18, block_num * self.cdv, 0, release=False) != 0:
# release the card
self.cs(1)
raise OSError(5) # EIO raise OSError(5) # EIO
offset = 0 offset = 0
mv = memoryview(buf) mv = memoryview(buf)
while nblocks: while nblocks:
# receive the data and release card
self.readinto(mv[offset : offset + 512]) self.readinto(mv[offset : offset + 512])
offset += 512 offset += 512
nblocks -= 1 nblocks -= 1