What is a bootable TF card?

• A bootable TF card is an TF card that has a bootloader installed on it.
• A bootable TF card is also known as a boot disk, which your SBC can boot-up from.

Why do we need a bootable TF card?

• You can release your custom ROM as a bootable TF card, in order to speed up the testing and development process.
• You can use a bootable TF card to do system/file recovery, in the event that your SBC is unable to boot from the eMMC.

Download U-Boot for (VIM1/VIM2/VIM3/VIM3L/VIM1S/VIM4), or get the correct bootloader blob for your TF card and manually build U-Boot. Regardless of which method you choose, you need to remember that there are different bootloader blobs for different boot disks/media.

Insert the TF card into your PC, and unmount it:

$ sudo umount /dev/sdX1

Format the TF card as FAT32:

$ sudo mkfs.vfat /dev/sdX1

Run dd to write the U-Boot blob into the first sector of TF card:

$ sudo dd if=u-boot.bin.sd.bin of=/dev/sdX conv=fsync,notrunc bs=1 count=444
$ sudo dd if=u-boot.bin.sd.bin of=/dev/sdX conv=fsync,notrunc bs=512 skip=1 seek=1

$ sudo dd if=u-boot.bin.sd.bin.signed of=/dev/sdX conv=fsync,notrunc bs=1 count=444
$ sudo dd if=u-boot.bin.sd.bin.signed of=/dev/sdX conv=fsync,notrunc bs=512 skip=1 seek=1

Eject the TF card from your PC:

$ sudo eject /dev/sdX

You need to Setup Serial Debug Tool fisrt, then insert the Bootable TF card into your SBC and power on.

If your SBC has successfully booted from the TF card, you should get this Terminal print-out:

GXL:BL1:9ac50e:a1974b;FEAT:ADFC318C;POC:3;RCY:0;EMMC:0;READ:0;CHK:AA;SD:0;READ:0;0.0;CHK:0;
no sdio debug board detected 
TE: 194208
 
BL2 Built : 13:48:56, Sep 23 2016. 
gxl g7459bd4 - jianxin.pan@droid06
 
set vcck to 1120 mv
set vddee to 1000 mv
Board ID = 6
CPU clk: 1200MHz
DQS-corr enabled
DDR scramble enabled
DDR3 chl: Rank0+1 @ 792MHz - PASS
Rank0: 1024MB(auto)-2T-11
Rank1: 1024MB(auto)-2T-11
DataBus test pass!
AddrBus test pass!
Load fip header from SD, src: 0x0000c200, des: 0x01400000, size: 0x00004000
New fip structure!
Load bl30 from SD, src: 0x00010200, des: 0x01100000, size: 0x0000d600
Load bl31 from SD, src: 0x00020200, des: 0x10100000, size: 0x00015400
Load bl33 from SD, src: 0x00038200, des: 0x01000000, size: 0x000a3400
NOTICE:  BL3-1: v1.0(debug):2e39a99
...