sd_spi.c

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#include "sd_spi.h"
 
uint8_t sd_crc7(const uint8_t* data, uint8_t len) {
    uint8_t crc = 0;
    for (uint8_t i = 0; i < len; ++i) {
        for (int bit = 7; bit >= 0; --bit) {
            uint8_t in = (uint8_t)(((data[i] >> bit) & 1U) ^ ((crc >> 6) & 1U));
            crc = (uint8_t)((crc << 1) & 0x7FU);
            if (in) {
                crc ^= 0x09U;
            }
        }
    }
    return crc;
}
 
void sd_command_frame(uint8_t out[6], uint8_t index, uint32_t argument) {
    out[0] = (uint8_t)(0x40U | (index & 0x3FU));
    out[1] = (uint8_t)(argument >> 24);
    out[2] = (uint8_t)(argument >> 16);
    out[3] = (uint8_t)(argument >> 8);
    out[4] = (uint8_t)argument;
    out[5] = (uint8_t)((sd_crc7(out, 5) << 1) | 1U);
}
 
bool sd_r7_ok(const uint8_t r7[4]) {
    return (r7[2] & 0x0FU) == ((SD_CMD8_ARG >> 8) & 0x0FU) &&
           r7[3] == (SD_CMD8_ARG & 0xFFU);
}
 
bool sd_cid_ok(const uint8_t cid[16]) {
    /* A floating MISO reads all 0xFF, and 16 x 0xFF happens to satisfy the
     * CRC7 (CRC7 of 15 x 0xFF is 0x7F). Reject uniform contents first. */
    bool all_ff = true, all_00 = true;
    for (uint8_t i = 0; i < 16; ++i) {
        all_ff = all_ff && cid[i] == 0xFFU;
        all_00 = all_00 && cid[i] == 0x00U;
    }
    if (all_ff || all_00) {
        return false;
    }
    return cid[15] == (uint8_t)((sd_crc7(cid, 15) << 1) | 1U);
}