linguini1 commented on code in PR #18543:
URL: https://github.com/apache/nuttx/pull/18543#discussion_r2943060168
##########
Documentation/components/drivers/special/sdio.rst:
##########
@@ -31,3 +31,36 @@ SDIO Device Drivers
- **Examples**: ``arch/arm/src/stm32/stm32_sdio.c`` and
``drivers/mmcsd/mmcsd_sdio.c``
+
+Implementing an SDIO lower-half
+===============================
+
+When implementing a new SDMMC controller driver (SDIO lower-half), it must
+provide the interface defined in ``struct sdio_dev_s``.
+
+Call-flow
+---------
+
+The MMCSD upper-half (``drivers/mmcsd/mmcsd_sdio.c``) interacts with the
+lower-half by sending commands and receiving responses:
+
+1. ``SDIO_SENDCMD``: Send the command (e.g., CMD2, CMD9).
Review Comment:
I believe the call flow is more complex than this.
##########
drivers/mmcsd/mmcsd_sdio.c:
##########
@@ -606,6 +606,12 @@ static void mmcsd_decode_csd(FAR struct mmcsd_state_s
*priv, uint32_t csd[4])
bool permwriteprotect;
bool tmpwriteprotect;
+ /* Best-effort sanity check for misaligned or missing-CRC CSD; the
+ * lower-half is responsible for returning the correct 128-bit layout.
+ */
+
+ DEBUGASSERT(csd[0] != 0);
Review Comment:
This is not correct. First , `csd[0]` is 32 bits, so this doesn't just check
that the first byte is 0.
Second, is it ever possible that the first byte (the CRC) is 0 naturally?
Are you able to test this on any targets?
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