命令boot执行 bootcmd。

bootcmd=run distro_bootcmd

distro_bootcmd=setenv nvme_need_init; for target in ${boot_targets}; do run bootcmd_${target}; done

boot_targets=usb0 mmc1 mmc0 nvme0 pxe dhcp sf0

依次调用bootcmd_usb0 bootcmd_mmc1 bootcmd_mmc0 bootcmd_nvme0等。

bootcmd_usb0=devnum=0; run usb_boot

usb_boot=
  usb start; 
  if usb dev ${devnum}; then 
    devtype=usb; 
    run scan_dev_for_boot_part; 
  fi

scan_dev_for_boot_part=
  part list ${devtype} ${devnum} -bootable devplist; 
  env exists devplist || setenv devplist 1; 
  for distro_bootpart in ${devplist}; do 
    if fstype ${devtype} ${devnum}:${distro_bootpart} bootfstype; then 
      run scan_dev_for_boot; 
    fi; 
  done; 
  setenv devplist

scan_dev_for_boot=
  echo Scanning ${devtype} ${devnum}:${distro_bootpart}...; 
  for prefix in ${boot_prefixes}; do 
    run scan_dev_for_extlinux; 
    run scan_dev_for_scripts; 
  done;
  run scan_dev_for_efi;

当前设备没有usb存储设备，暂时先看别的。

bootcmd_mmc1=devnum=1; run mmc_boot

mmc_boot=
  if mmc dev ${devnum}; then 
    devtype=mmc; 
    run scan_dev_for_boot_part; 
  fi

scan_dev_for_scripts=
  for script in ${boot_scripts}; do 
    if test -e ${devtype} ${devnum}:${distro_bootpart} ${prefix}${script}; then 
      echo Found U-Boot script ${prefix}${script}; 
      run boot_a_script; 
      echo SCRIPT FAILED:
       continuing...; 
    fi; 
  done

boot_a_script=
  load ${devtype} ${devnum}:${distro_bootpart} ${scriptaddr} ${prefix}${script}; 
  source ${scriptaddr}

scan_dev_for_extlinux=
  if test -e ${devtype} ${devnum}:${distro_bootpart} ${prefix}${boot_syslinux_conf}; then 
    echo Found ${prefix}${boot_syslinux_conf}; 
    run boot_extlinux; 
    echo SCRIPT FAILED: 
    continuing...; 
  fi

boot_syslinux_conf=extlinux/extlinux.conf

boot_extlinux=
  sysboot ${devtype} ${devnum}:${distro_bootpart} any ${scriptaddr} ${prefix}${boot_syslinux_conf}