Add initial SD card (SPI mode) decoder.

[libsigrokdecode.git] / decoders / sdcard_spi / __init__.py

diff --git a/decoders/sdcard_spi/__init__.py b/decoders/sdcard_spi/__init__.py
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+##
+## This file is part of the sigrok project.
+##
+## Copyright (C) 2012 Uwe Hermann <uwe@hermann-uwe.de>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 2 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, write to the Free Software
+## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+##
+
+'''
+SD card (SPI mode) low-level protocol decoder.
+
+TODO: Description.
+
+Most SD cards can be accessed via two different protocols/modes: SD mode
+or SPI mode.
+
+All SD cards are in SD mode upon powerup. They can be switched to SPI mode
+using a special method involving CMD0 (see spec). Once in SPI mode, the mode
+can no longer be changed without a power-cycle of the card.
+
+SPI mode properties (differences to SD mode):
+ * The 'sdcard_spi' PD stacks on top of the 'spi' PD. This is not possible
+   for the 'sdcard_sd' PD, as that protocol is not SPI related at all.
+   Hence 'sdcard_spi' and 'sdcard_sd' are two separate PDs.
+ * The state machines for SPI mode and SD mode are different.
+ * In SPI mode, data transfers are byte-oriented (commands/data are multiples
+   of 8 bits, with the CS# pin asserted respectively), unlike SD mode where
+   commands/data are bit-oriented with parallel transmission of 1 or 4 bits.
+ * While the SPI mode command set has some commands in common with the
+   SD mode command set, they are not the same and also not a subset/superset.
+   Some commands are only available in SD mode (e.g. CMD2), some only
+   in SPI mode (e.g. CMD1).
+ * Response types of commands also differ between SD mode and SPI mode.
+   E.g. CMD9 has an R2 response in SD mode, but R1 in SPI mode.
+ * The commands and functions in SD mode defined after version 2.00 of the
+   spec are NOT supported in SPI mode.
+ * SPI mode: The selected SD card ALWAYS responds to commands (unlike SD mode).
+ * Upon data retrieval problems (read operations) the card will respond with
+   an error response (and no data), as opposed to a timeout in SD mode.
+ * SPI mode: For every data block sent to the card (write operations) the host
+   gets a data response token from the card.
+ * SDSC: A data block can be max. one card write block, min. 1 byte.
+ * SDHC/SDXC: Block length is fixed to 512. The block length set by CMD16
+   is only used for CDM42 (not for memory data transfers). Thus, partial
+   read/write operations are disabled in SPI mode.
+ * SPI mode: Write protected commands (CMD28, CMD29, CMD30) are not supported.
+ * The SD mode state machine is NOT used. All commands that are supported
+   in SPI mode are always available.
+ * Per default the card is in CRC OFF mode. Exception: CMD0 (which is used to
+   switch to SPI mode) needs a valid CRC.
+ * The APP_CMD status bit is not available in SPI mode.
+ * TODO: Switch function command differences.
+ * In SPI mode cards cannot guarantee their speed class (the host should
+   assume class 0, no matter what the card indicates).
+ * The RCA register is not accessible in SPI mode.
+
+Details:
+TODO
+'''
+
+from .pd import *
+