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Decoder sdcard: look at the transmission bit for command or response decoding

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Description of the bug fix:
When a command is not supported by the sdcard, the command is silently
dropped with no response. The host will then either reemit the same command
or give up. This causes the previous decoder implementation to go out of
sync and wrongly decode the next message as a response even though it's not.

This patch looks at the transmission bit instead to make sure the
decoding is correct.
This commit is contained in:
Pierre-Olivier Vauboin 2021-02-15 18:49:07 +01:00
parent ce545fa88c
commit 162cdb44ee
1 changed files with 30 additions and 1 deletions
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31
libsigrokdecode4DSL/decoders/sdcard_sd/pd.py
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@ -147,6 +147,14 @@ class Decoder(srd.Decoder):
self.token[n - 1].es += self.token[n - 1].ss - self.token[n - 2].ss
return True
def is_from_host(self):
# CMD[46:46]: Transmission bit (1 == host), (0 == card)
return self.token[1].bit == 1
def is_from_card(self):
# CMD[46:46]: Transmission bit (1 == host), (0 == card)
return self.token[1].bit == 0
def handle_common_token_fields(self):
s = self.token
@ -192,7 +200,15 @@ class Decoder(srd.Decoder):
if not self.get_token_bits(cmd_pin, 48):
return
if not self.is_from_host():
# Bad state due to a decoding mistake or a protocol error,
# drop the current token to try to recover from this situation.
self.token, self.state = [], St.GET_COMMAND_TOKEN
return
self.handle_cmd()
def handle_cmd(self):
self.handle_common_token_fields()
# Handle command.
@ -406,6 +422,7 @@ class Decoder(srd.Decoder):
# - Bits[00:00]: End bit (always 1)
if not self.get_token_bits(cmd_pin, 48):
return
assert(self.is_from_card())
self.handle_common_token_fields()
self.putr(Ann.RESPONSE_R1)
self.puta(0, 31, [Ann.DECODED_F, ['Card status', 'Status', 'S']])
@ -417,6 +434,7 @@ class Decoder(srd.Decoder):
# R1b: Same as R1 with an optional busy signal (on the data line)
if not self.get_token_bits(cmd_pin, 48):
return
assert(self.is_from_card())
self.handle_common_token_fields()
self.puta(0, 31, [Ann.DECODED_F, ['Card status', 'Status', 'S']])
self.putr(Ann.RESPONSE_R1B)
@ -431,6 +449,7 @@ class Decoder(srd.Decoder):
# - Bits[000:000]: End bit (always 1)
if not self.get_token_bits(cmd_pin, 136):
return
assert(self.is_from_card())
# Annotations for each individual bit.
for bit in range(len(self.token)):
self.putf(bit, bit, [Ann.BIT_0 + self.token[bit].bit, ['%d' % self.token[bit].bit]])
@ -461,6 +480,7 @@ class Decoder(srd.Decoder):
# - Bits[00:00]: End bit (always 1)
if not self.get_token_bits(cmd_pin, 48):
return
assert(self.is_from_card())
self.putr(Ann.RESPONSE_R3)
# Annotations for each individual bit.
for bit in range(len(self.token)):
@ -486,6 +506,7 @@ class Decoder(srd.Decoder):
# - Bits[00:00]: End bit (always 1)
if not self.get_token_bits(cmd_pin, 48):
return
assert(self.is_from_card())
self.handle_common_token_fields()
self.puta(0, 15, [Ann.DECODED_F, ['Card status bits', 'Status', 'S']])
self.puta(16, 31, [Ann.DECODED_F, ['Relative card address', 'RCA', 'R']])
@ -504,6 +525,7 @@ class Decoder(srd.Decoder):
# - Bits[00:00]: End bit (always 1)
if not self.get_token_bits(cmd_pin, 48):
return
assert(self.is_from_card())
self.handle_common_token_fields()
self.putr(Ann.RESPONSE_R7)
@ -551,4 +573,11 @@ class Decoder(srd.Decoder):
# Call the respective handler method for the response.
s = 'handle_response_%s' % self.state.value[13:].lower()
handle_response = getattr(self, s)
handle_response(cmd_pin)
# AssertionError can be raised when the token we are trying
# to handle as a response is in fact a command.
# (Transmission bit is 1). Just re-handle the token as command.
try:
handle_response(cmd_pin)
except AssertionError:
self.handle_cmd()