Add initial SD card (SPI mode) decoder.

This is work in progress, but it already works partially, and can be used
for actual decodes of some commands.

This PD stacks on top of the SPI protocol decoder.

1 files changed, 74 insertions, 0 deletions

diff --git a/decoders/sdcard_spi/__init__.py b/decoders/sdcard_spi/__init__.py
new file mode 100644
index 0000000..3b85f58
--- /dev/null
+++ b/decoders/sdcard_spi/__init__.py
@@ -0,0 +1,74 @@
+##
+## 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 *
+