大家好！
我成功地用tf卡把emmc移植上了系统，也可以从emmc正常启动系统了。现在有这么一个问题：从emmc启动系统可以正常工作，但是下次设备没有插入tf卡的话，系统就无法进入到文件系统中，下面是没有tf卡的启动信息：
U-Boot SPL 2014.04-00014-g47880f5 (Apr 22 2014 - 13:23:54)
reading args
spl_load_image_fat_os: error reading image args, err - -1
reading u-boot.img
reading u-boot.img
U-Boot 2014.04-00014-g47880f5 (Apr 22 2014 - 13:23:54)
I2C: ready
DRAM: 512 MiB
NAND: 0 MiB
MMC: OMAP SD/MMC: 0, OMAP SD/MMC: 1
*** Warning - readenv() failed, using default environment
Net: <ethaddr> not set. Validating first E-fuse MAC
cpsw, usb_ether
Hit any key to stop autoboot: 0
gpio: pin 53 (gpio 53) value is 1
Card did not respond to voltage select!
mmc0(part 0) is current device
Card did not respond to voltage select!
gpio: pin 56 (gpio 56) value is 0
gpio: pin 55 (gpio 55) value is 0
gpio: pin 54 (gpio 54) value is 0
mmc1(part 0) is current device
gpio: pin 54 (gpio 54) value is 1
SD/MMC found on device 1
reading uEnv.txt
1698 bytes read in 7 ms (236.3 KiB/s)
gpio: pin 55 (gpio 55) value is 1
Loaded environment from uEnv.txt
Importing environment from mmc ...
Checking if uenvcmd is set ...
gpio: pin 56 (gpio 56) value is 1
Running uenvcmd ...
reading zImage
4382704 bytes read in 253 ms (16.5 MiB/s)
reading initrd.img
2957458 bytes read in 171 ms (16.5 MiB/s)
reading /dtbs/am335x-boneblack.dtb
25130 bytes read in 9 ms (2.7 MiB/s)
Kernel image @ 0x82000000 [ 0x000000 - 0x42dff0 ]
## Flattened Device Tree blob at 88000000
Booting using the fdt blob at 0x88000000
Using Device Tree in place at 88000000, end 88009229
Starting kernel ...
Uncompressing Linux... done, booting the kernel.
[ 0.355834] omap2_mbox_probe: platform not supported
[ 0.362420] tps65217-bl tps65217-bl: no platform data provided
[ 0.426610] bone-capemgr bone_capemgr.9: slot #0: No cape found
[ 0.463719] bone-capemgr bone_capemgr.9: slot #1: No cape found
[ 0.500827] bone-capemgr bone_capemgr.9: slot #2: No cape found
[ 0.537936] bone-capemgr bone_capemgr.9: slot #3: No cape found
[ 0.556723] omap_hsmmc mmc.5: of_parse_phandle_with_args of 'reset' failed
[ 0.618254] pinctrl-single 44e10800.pinmux: pin 44e10854 already requested by 44e10800.pinmux; cannot claim for gpio-leds.8
[ 0.629962] pinctrl-single 44e10800.pinmux: pin-21 (gpio-leds.8) status -22
[ 0.637245] pinctrl-single 44e10800.pinmux: could not request pin 21 on device pinctrl-single
Loading, please wait...
modprobe: chdir(3.8.13): No such file or directory
Gave up waiting for root device. Common problems:
- Boot args (cat /proc/cmdline)
- Check rootdelay= (did the system wait long enough?)
- Check root= (did the system wait for the right device?)
- Missing modules (cat /proc/modules; ls /dev)
ALERT! /dev/mmcblk1p2 does not exist. Dropping to a shell!
modprobe: chdir(3.8.13): No such file or directory
modprobe: chdir(3.8.13): Žo such file or directory
modprobe: chdir(3.8.13): No such file or directory
modprobe: chdir(3.8.13): No such file or directory
modprobe: chdir(3.8.13): No such file or directory
modprobe: chdir(3.8.13): No such file or directory
BusyBox v1.20.2 (Debian 1:1.20.0-7) built-in shell (ash)
Enter 'help' for a list of built-in commands.
/bin/sh: can't access tty; job control turned off
(initramfs)
后来发现是环境变量的问题：板子的环境变量uEnv.txt中
“mmcroot=/dev/mmcblk1p2 ro”
进入系统后，将它改为
“mmcroot=/dev/mmcblk0p2 ro”，这样拔掉sd卡后就可以从emmc正常启动系统了。
但是，我想问的是：怎么能够让emmc默认是/dev/mmcblk0p2呢，不管加了什么其他的mmc设备都不会影响从emmc中正常的启动系统。
望赐教！！！
