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Add data response token validation in SD/MMC write operations #6

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Add data response token validation in SD/MMC write operations #6

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Initial plan
Copilot Dec 18, 2025
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Add data response token validation in SD/MMC write operations
Copilot Dec 18, 2025
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Improve data response token comment clarity
Copilot Dec 18, 2025
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20 changes: 19 additions & 1 deletion mmc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,15 @@
#define STATE_ADDR_ERR (1 << 5)
#define STATE_PARAM_ERR (1 << 6)

// data response token for write operations
// 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

#define TIMEOUT 0x7fff

// private helper functions
Expand Down Expand Up @@ -332,7 +341,16 @@ 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;
Expand Down