编译固件

bitbake -k core-image-minimal
//编译出的固件
core-image-minimal-imx8mmevk-20190508073946.rootfs.sdcard.bz2
//压缩固件
sudo bzip2 -d core-image-minimal-imx8mmevk.sdcard　
//得到固件
core-image-minimal-imx8mmevk.sdcard
//写入SD卡
sudo dd if=imx8mmevk-avs-synaptics-1.9.sdcard of=/dev/sd<part> bs=1M && sync

1. 第一次写入的SD卡为8GB/SanDisk , 提示如下，并没有成功启动

U-Boot 2018.03-imx_v2018.03_4.14.78_1.0.0_ga+g7ade5b4 (May 08 2019 - 08:18:47 +0000)

CPU:   Freescale i.MX8MMQ rev1.0 1800 MHz (running at 1200 MHz)
CPU:   Commercial temperature grade (0C to 95C) at 47C
Reset cause: POR
Model: FSL i.MX8MM EVK board
DRAM:  2 GiB
TCPC:  Vendor ID [0x1fc9], Product ID [0x5110], Addr [I2C1 0x52]
Power supply on USB2
TCPC:  Vendor ID [0x1fc9], Product ID [0x5110], Addr [I2C1 0x50]
MMC:   FSL_SDHC: 0, FSL_SDHC: 1

// 这里提示错误
Loading Environment from MMC... *** Warning - No block device, using default environment

Failed (-5)
No panel detected: default to MIPI2HDMI
adv7535_init: Can't find device id=0x3d, on bus 1
Display: MIPI2HDMI (1920x1080)
Video: 1920x1080x24
In:    serial
Out:   serial
Err:   serial

 BuildInfo:
  - ATF d6451cc
  - U-Boot 2018.03-imx_v2018.03_4.14.78_1.0.0_ga+g7ade5b4

flash target is MMC:0
MMC card init failed!

2. 第二次写入的SD卡为256Mb , 可以成功启动

U-Boot 2018.03-imx_v2018.03_4.14.78_1.0.0_ga+g7ade5b4 (May 08 2019 - 08:18:47 +0000)

CPU:   Freescale i.MX8MMQ rev1.0 1800 MHz (running at 1200 MHz)
CPU:   Commercial temperature grade (0C to 95C) at 50C
Reset cause: POR
Model: FSL i.MX8MM EVK board
DRAM:  2 GiB
TCPC:  Vendor ID [0x1fc9], Product ID [0x5110], Addr [I2C1 0x52]
Power supply on USB2
TCPC:  Vendor ID [0x1fc9], Product ID [0x5110], Addr [I2C1 0x50]
MMC:   FSL_SDHC: 0, FSL_SDHC: 1
Loading Environment from MMC... *** Warning - bad CRC, using default environment

Failed (-5)
No panel detected: default to MIPI2HDMI
adv7535_init: Can't find device id=0x3d, on bus 1
Display: MIPI2HDMI (1920x1080)
Video: 1920x1080x24
In:    serial
Out:   serial
Err:   serial

 BuildInfo:
  - ATF d6451cc
  - U-Boot 2018.03-imx_v2018.03_4.14.78_1.0.0_ga+g7ade5b4

switch to partitions #0, OK
mmc0 is current device
flash target is MMC:0
Net:   
Warning: ethernet@30be0000 using MAC address from ROM
eth0: ethernet@30be0000
Fastboot: Normal
Normal Boot
Hit any key to stop autoboot:  0 
switch to partitions #0, OK
mmc0 is current device
** Unable to read file boot.scr **
23065088 bytes read in 1249 ms (17.6 MiB/s)
Booting from mmc ...
43009 bytes read in 16 ms (2.6 MiB/s)
## Flattened Device Tree blob at 43000000
   Booting using the fdt blob at 0x43000000
   Using Device Tree in place at 0000000043000000, end 000000004300d800

Starting kernel ...

结论

8GB/SanDisk的提示,应该有些SD卡识别不了导致

Loading Environment from MMC... *** Warning - No block device, using default environment