From 169c6c58334c605f3fb690b11c6a17ad6ed2b99d Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 18 Dec 2025 12:22:19 +0000
Subject: [PATCH 1/3] Initial plan


From f230fc3880bce12ca0f2182af09b6422397c498b Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 18 Dec 2025 12:27:15 +0000
Subject: [PATCH 2/3] Add data response token validation in SD/MMC write
 operations

Co-authored-by: sittner <1475582+sittner@users.noreply.github.com>
---
 mmc.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/mmc.c b/mmc.c
index 07f219e..9a6e9e7 100644
--- a/mmc.c
+++ b/mmc.c
@@ -99,6 +99,14 @@
 #define STATE_ADDR_ERR      (1 << 5)
 #define STATE_PARAM_ERR     (1 << 6)
 
+// data response token for write operations
+// format: xxx0sss1, where sss indicates:
+// 010 (0x05 when masked with 0x1F) = Data accepted
+// 101 (0x0B when masked with 0x1F) = Data rejected, CRC error
+// 110 (0x0D when masked with 0x1F) = Data rejected, write error
+#define DATA_RESPONSE_MASK     0x1F
+#define DATA_RESPONSE_ACCEPTED 0x05
+
 #define TIMEOUT 0x7fff
 
 // private helper functions
@@ -332,7 +340,16 @@ void drive_write_block(uint32_t blkno, const uint8_t *data) {
   spi_send_byte(0xff);
   spi_send_byte(0xff);
 
-  // wait while card is busy
+  // read and verify data response token
+  // the card responds with a token indicating if data was accepted
+  uint8_t response = spi_rec_byte();
+  if ((response & DATA_RESPONSE_MASK) != DATA_RESPONSE_ACCEPTED) {
+    // data rejected: either CRC error (0x0B) or write error (0x0D)
+    tfs_last_error = TFS_ERR_IO;
+    return;
+  }
+
+  // wait while card is busy (card pulls line low during programming)
   if (!wait_byte(0xff)) {
     tfs_last_error = TFS_ERR_IO;
     return;

From a8cee4b4ae562cd2dde73ac4505aa0cc834dfa8e Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 18 Dec 2025 12:28:31 +0000
Subject: [PATCH 3/3] Improve data response token comment clarity

Co-authored-by: sittner <1475582+sittner@users.noreply.github.com>
---
 mmc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mmc.c b/mmc.c
index 9a6e9e7..a0e41e1 100644
--- a/mmc.c
+++ b/mmc.c
@@ -100,10 +100,11 @@
 #define STATE_PARAM_ERR     (1 << 6)
 
 // data response token for write operations
-// format: xxx0sss1, where sss indicates:
-// 010 (0x05 when masked with 0x1F) = Data accepted
-// 101 (0x0B when masked with 0x1F) = Data rejected, CRC error
-// 110 (0x0D when masked with 0x1F) = Data rejected, write error
+// format: xxx0sss1 (8 bits), where bits [3:1] (sss) indicate status:
+// - sss=010: Data accepted    → full token masked = 0x05 (xxx00101)
+// - sss=101: CRC error        → full token masked = 0x0B (xxx01011)
+// - sss=110: Write error      → full token masked = 0x0D (xxx01101)
+// mask extracts bits [4:0] to include the fixed bit 0 (always 1) and bit 4 (always 0)
 #define DATA_RESPONSE_MASK     0x1F
 #define DATA_RESPONSE_ACCEPTED 0x05