SD_IO_CCCR_FN_ENABLE
rv = sdmmc_io_read_1(sf0, SD_IO_CCCR_FN_ENABLE);
sdmmc_io_write_1(sf0, SD_IO_CCCR_FN_ENABLE, rv);
rv = sdmmc_io_read_1(sf0, SD_IO_CCCR_FN_ENABLE);
sdmmc_io_write_1(sf0, SD_IO_CCCR_FN_ENABLE, rv);