Yocto构建时出现U-Boot编译问题，编译错误信息如下：
WARNING: u-boot-mys6ulx-2016.03-r0 do_fetch: Failed to fetch URL \
git:////home/KevinChen/MYiR-iMX-uboot;protocol=file;branch=mys-6ulx, \
attempting MIRRORS if available
ERROR: u-boot-mys6ulx-2016.03-r0 do_fetch: Fetcher failure: \
Unable to find revision 38cc50da55a891ba0ac09346f3a7a6cbb4a20970 \
in branch mys-6ulx even from upstream
ERROR: u-boot-mys6ulx-2016.03-r0 do_fetch: Function failed: \
Fetcher failure for URL: 'git:////home/KevinChen/MYiR-iMX-uboot;i \
protocol=file;branch=mys-6ulx'. \
Unable to fetch URL from any source.
ERROR: Logfile of failure stored in: /home/KevinChen/MYD-Y6ULX-devel/fsl- \
release-yocto/myd-y6uly2/tmp/work/myd_y6ull14x14-poky-linux-gnueabi/ \
u-boot-mys6ulx/2016.03-r0/temp/log.do_fetch.4991
ERROR: Task 206 (/home/KevinChen/MYD-Y6ULX-devel/fsl-release-yocto/sources \
/meta-myir-imx6ulx/recipes-bsp/u-boot/u-boot-mys6ulx_2016.03.bb, \
do_fetch) failed with exit code '1'
NOTE: Tasks Summary: Attempted 3116 tasks of which \
3115 didn't need to be rerun and 1 failed.
No currently running tasks (1771 of 3136)
Summary: 1 task failed:
/home/KevinChen/MYD-Y6ULX-devel/fsl-release-yocto/sources/ \
meta-myir-imx6ulx/recipes-bsp/ \
u-boot/u-boot-mys6ulx_2016.03.bb, do_fetch
Summary: There were 3 WARNING messages shown.
Summary: There were 2 ERROR messages shown, returning a non-zero exit code.
出现这种情况是由于U-Boot更新后，Yocto没有更新的对应的版本。 修改步骤如下：
- 进⼊U-Boot源码⽬录，使⽤"git log"查看commit id并复制
- 修改Yocto源码⽬录下的"source/meta-myir-imx6ulx/recipes-bsp/u-boot/u-boot-mys6ulx_2016.03.bb"⽂件中的SRCREV变
量为commit id即可。