sdcard_sd: Decode commands always as command

The SD card decoder predicts always the next token type from the
current token type. This is working if the SD card is responding as
expected.
But if the card is not responding, the prediction is wrong. A second
command token is decoded as a response token.

To fix this behavior the decoder state is set to St.GET_COMMAND_TOKEN,
if the current token is a command token.

Author: harper23

decoders/sdcard_sd/pd.py

@@ -142,6 +142,11 @@ def get_token_bits(self, cmd_pin, n):
         self.token.append(Bit(self.samplenum, self.samplenum, cmd_pin))
         if len(self.token) > 0:
             self.token[len(self.token) - 2].es = self.samplenum
+            # check the transmission bit if this is a command
+            if len(self.token) == 2:
+                transmission = self.token[1].bit
+                if transmission:
+                    self.state = St.GET_COMMAND_TOKEN
         if len(self.token) < n:
             return False
         self.token[n - 1].es += self.token[n - 1].ss - self.token[n - 2].ss