背景: MLU220 SOM 板无法从网络加载，选择从 SD 卡加载，烧录失败,提示下面日志中的红色信息，如何解决？

按照《寒武纪SOM%20SDK使用及开发指南_v1.7.0.pdf》中  第 3.2.2 SD 加载   执行操作

日志输出

CAMBR-C20E# C20E ROM: v1.0(release):ac35090

C20E ROM: Built : 20:20:53, Jun 11 2019

Norflash id: 0x709d

C20E ROM boot done.

C20E PREBOOT: Built : 16:49:16, Jun 21 2021

C20E PREBOOT: v120

Norflash id: 0x709d

No config.bin exists

Read Serial Number From NorFlash

Board Serial Number: 362103300418

pcie link up error, ret 2

ddr ok loop 0

Going to boot the atf bl1

C20E preboot done.

NOTICE:  Booting Trusted Firmware

NOTICE:  BL1: v1.5(release):4.9.5

NOTICE:  BL1: Built : 16:49:15, Jun 21 2021

NOTICE:  Norflash id: 0x709d

NOTICE:  BL1: Booting BL2

NOTICE:  Norflash id: 0x709d

NOTICE:  BL2: v1.5(release):4.9.5

NOTICE:  BL2: Built : 16:49:15, Jun 21 2021

NOTICE:  BL1: Booting BL31

NOTICE:  BL31: v1.5(release):4.9.5

NOTICE:  BL31: Built : 16:49:15, Jun 21 2021

U-Boot 2017.07-cambricon4.9.5 (Jun 21 2021 - 16:49:11 +0800), Build: jenkins-DRIVER-release_mlu220edge_driver_master_daily_pipeline-911

CPU  : Cambricon Technologies C20E

DRAM:  1 GiB

MMC:   sdhci@8000040000: 0, sdhci@8000044000: 1, sdhci@8000048000: 2

In:    serial

Out:   serial

Err:   serial

Card did not respond to voltage select!

** Bad device mmc 2 **

## Warning: Input data exceeds 1048576 bytes - truncated

## Info: input data size = 1048578 = 0x100002

try to get uenv_extra.txt from emmc...

119 bytes read in 7 ms (16.6 KiB/s)

## Info: input data size = 120 = 0x78

Net:   eth0: ethernet@8000054000

Hit any key to stop autoboot:  0

CAMBR-C20E# env default -a

## Resetting to default environment

CAMBR-C20E# setenv force_update force_update=SD

CAMBR-C20E# run set_force_update

force_update=SD

Card did not respond to voltage select!

Card did not respond to voltage select!

** Bad device mmc 2 **

## Executing script at 1008000000

Wrong image format for "source" command

## Error: "recovery_boot" not defined