遇到的两个问题 :
下载buildroot-2019.05-rc2版本，构建freescale_imx8mmevk_defconfig(由于imx8mmevk 和imx8mqevk差别不大，因此在imx8mqevk的基础上得到imx8mmevk) , 构建出的固件烧录到开发板，发现无法启动 make freescale_imx8mmevk_defconfig make // buildroot-2019.05-rc2/output/images 目录得到固件 ├── bl31.bin ├── boot.vfat ├── fsl-imx8mm-evk.dtb ├── Image ├── imx8-boot-sd.bin ├── imx-boot-imx8mmevk-sd.bin-flash_evk ├── lpddr4_pmu_train_fw.bin ├── rootfs.ext2 ├── rootfs.ext4 -> rootfs.ext2 ├── rootfs.tar ├── sdcard.img ├── signed_hdmi_imx8m.bin ├── u-boot.bin ├── u-boot.imx ├── u-boot.itb ├── u-boot-nodtb.bin ├── u-boot-spl.bin └── u-boot-spl-ddr.bin烧录固件之后，发现一行打印也没有，代表uboot 都无法启动，而buildroot uboot 打包固件的脚本对应 : buildroot-2019.05-rc2/board/freescale/common/imx/imx8-bootloader-prepare.sh ，应该是该脚本出现问题，该问题并没有深入研究，
而是把Yocto 构建出的最小系统得到的imx-boot-imx8mmevk-sd.bin-flash_evk直接放到buildroot 打包固件的配置文件中
buildroot-2019.05-rc2/board/freescale/common/imx/genimage.cfg.template_imx8 image sdcard.img { hdimage { } partition imx-boot { in-partition-table = "no" # image = "imx8-boot-sd.bin" # 这里是重点 image = "imx-boot-imx8mmevk-sd.bin-flash_evk" offset = %IMXOFFSET% } partition boot { partition-type = 0xC bootable = "true" image = "boot.vfat" offset = 8M } partition rootfs { partition-type = 0x83 image = "rootfs.ext2" } }替换了uboot之后，打包出的sdcard.img 烧录进去，确实可以启动，内核也启动起来了，但是无法进入文件系统
[ 4.194949] VSD_3V3: disabling [ 4.199098] ALSA device list: [ 4.202081] #0: wm8524-audio [ 4.205139] #1: imx-spdif [ 4.207946] #2: imx-audio-micfil [ 4.229743] EXT4-fs (mmcblk2p2): recovery complete [ 4.235308] EXT4-fs (mmcblk2p2): mounted filesystem with ordered data mode. Opts: (null) [ 4.243484] VFS: Mounted root (ext4 filesystem) on device 179:2. [ 4.251138] devtmpfs: mounted [ 4.254447] Freeing unused kernel memory: 1280K [ 4.274522] EXT4-fs (mmcblk2p2): re-mounted. Opts: data=ordered Starting syslogd: OK Starting klogd: OK Initializing random number generator... [ 4.310549] random: dd: uninitialized urandom read (512 bytes read) done. Starting network: OK // 起初以为是这里问题，没有加载音频相关的固件，后来想明白了，固件加载不成功，卡住也不合理。 [ 4.383016] imx-sdma 30bd0000.dma-controller: sdma firmware not ready! [ 4.389557] imx-uart 30860000.serial: [ 4.446690] imx-sdma 30bd0000.dma-controller: sdma firmware not ready! [ 4.453230] imx-uart 30860000.serial: Prepare for the RX slave dma failed! [ 4.560810] imx-sdma 30bd0000.dma-controller: sdma firmware not ready! [ 4.567366] imx-uart 30860000.serial: We cannot prepare for the TX slave dma! [ 4.577798] imx-sdma 30bd0000.dma-controller: sdma firmware not ready! [ 4.584355] imx-uart 30860000.serial: We cannot prepare for the TX slave dma! [ 4.591517] imx-sdma 30bd0000.dma-controller: sdma firmware not ready! [ 4.598071] imx-uart 30860000.serial: We cannot prepare for the TX slave dma! [ 62.567126] imx-sdma 30bd0000.dma-controller: external firmware not found, using ROM firmware [ 62.567554] imx-sdma 302c0000.dma-controller: external firmware not found, using ROM firmware [ 62.584223] imx-sdma 302b0000.dma-controller: external firmware not found, using ROM firmware遇到这问题，走了2天的冤枉路。继续找问题
NXP 最初提供的Yocto 编译出最小系统和Buildroot 最小文件系统做对比，对比差异发现区别很大，主要原因是 : Yocto 文件系统的启动方式是Systemd , 而 Buildroot 文件系统启动方式是 Sysvinitbuildroot 中文件系统启动方式切换到Systemd，和Yocto 对比发现差异还是很大最后查资料，通过把Yocto文件系统启动方式切换为Sysvinit，进行对比，发现差异较小，果然发现了问题 BR2_TARGET_GENERIC_GETTY_PORT="ttymxc0" 改为 BR2_TARGET_GENERIC_GETTY_PORT="ttymxc1" 对应的是串口登录 target/etc/ inittab ttymxc1::respawn:/sbin/getty -L ttymxc1 0 vt100 # GENERIC_SERIAL导致文件系统无法登录的原因应该是串口选择的不对，IMX8MM其实有两个串口，一个串口是Core-A53,另一个是Core-M4的.
buildroot-2017.02 中添加freescale_imx8mmevk_defconfig相关配置，编译到内核报错 : Incorrect selection of kernel headers: expected 4.14, got 4.9buildroot/support/scripts/check-kernel-headers.sh 在执行check-kernel-headers.sh时会检测这这个内核版本代码。
内核是4.14的，而交叉编译器这里选择的是4.9，双方不匹配导致。
buildroot -> Toolchain -> Custom kernel headers series 这里选择到4.14.x ，而问题是buildroot-2017.02 版本最高只支持到 4.9.x , buildroot 需要升级
参考am335x buildroot 编译报错解决 Incorrect selection of kernel headers: expected 3.2.x, got 4.6.x找到解决办法
