In BF548-EZKIT, mount SDIO MMC without "-o sync" option, then generate a big file in MMC card. After it finishes, umount MMC, message "FIFO ERROR: TX UNDERRUN" often appears.

Below is the log:
------------------
root:~> fdisk /dev/mmcblk0

The number of cylinders for this disk is set to 15856.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/mmcblk0: 4 heads, 16 sectors, 15856 cylinders
Units = cylinders of 64 * 512 bytes

        Device Boot    Start       End    Blocks   Id  System
/dev/mmcblk0p1             1      8193    262168   83  Linux
/dev/mmcblk0p2          8194     15856    245216    b  Win95 FAT32

Command (m for help): q

root:~>
root:~> mkdir /mnt/mmc
root:~> mkdosfs /dev/mmcblk0p2
mkdosfs 2.10 (22 Sep 2003)
root:~> mount -t msdos /dev/mmcblk0p2 /mnt/mmc
root:~> time dd if=/dev/zero of=/mnt/mmc/10m.bin bs=1M count=10
10+0 records in
10+0 records out
real    0m 3.55s
user    0m 0.00s
sys     0m 0.79s
root:~> ls /mnt/mmc
10m.bin
root:~> umount /mnt/mmc
FIFO ERROR: TX UNDERRUN