uboot mmc read / write command usage

mmc read is used to read the contents into memory,

mmc write is used to write the contents of memory to the mmc

Specific usage, 

mmc read <device num> addr blk # cnt [partition]

mmc write <device num> addr blk # cnt [partition]

mmc list

mmc device num is the device number, you can query through mmc list

addr is the memory address

blk # is the number of blocks within mmc

cnt number of blocks

Example:

mmc write 2 0x90000000 0x600 0x10

The memory 0x90000000, length 16x512 size data, write to 2 mmc device block at offset position of 0x600

mmc read 2 0x90000000 0x600 0x10

Mmc device of the second block starting at offset 0x600, 16x512 size of length data, read out to the memory at 0x90000000