Dear all, The eMMC 4.5 specification mentions that the CMD21 in class 2 is a SEND_TUNING BLOCK command. where as the SD card specification in the given link says CMD19 in class 2 is the SEND_TUNING_BLOCK http://www.scribd.com/doc/50685191/53/Figure-4-8-Send-Tuning-Block-Command. Also the implementation in the drivers/mmc/host/sdhci.c uses the CMD19 as the SEND_TUNING_BLOCK. Can anybody clarify why there is overlapping in this command number. May be my understand is wrong. In the MMC spec the CMD19 is BUS_TEST_W in class 0 and CMD21 is reserved till eMMC 4.41 version. But in the SD specification (given link) CMD19 is SEND_TUNING_BLOCK and CMD21 is reserved. Thanks and regards Girish K S -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html