U-Boot

Introduction

RK U-Boot is based on the open source U-Boot. It supports boot loader
mode and download mode. Boot loader mode is the normal mode of U-Boot.
Device usually releases under this mode. This mode mainly loads the
kernel from FLASH to SDRAM and boots the Operating System. User needs
to flash the device under the download mode. Keep the recover key
pressed while powering on the board, and it will enter download mode.
This chapter mainly talks about U-Boot.

Compilation

The compiling steps of U-Boot are similar to kernel's. You need to
write the configuration to ".config" first，run the command:

   cd SDK/u-boot
   make rk3128_defconfig

If you need to modify the configuration, run:

   make menuconfig

Compile:

   make

The following files are generated after successful compilation:

   RK3128MiniLoaderAll(L)_V2.20.bin
   uboot.img

RK3128MiniLoaderAll(L)_V2.20.bin and uboot.img use the feature of two
stages boot, which supports eMMC and NAND flash.

Burn

Open the burn tool, connect the USB OTG cable to the board, press and
hold the Recovery button when connecting to power supply, so that the
development board enters the U-Boot download mode. Select the required
Loader file in the burn tool and click Run, which is shown as below:

Confirm whether the new Loader is properly programmed

If you have successfully programmed your newly compiled Loader, you’ll
see information or similar information in the serial output when
booting:

   #Boot ver: 2015-01-05#2.19

If print time and version are consistent with that compiled by you,
meaning you’ve successfully updated the Loader.

Enter U-Boot command line mode

Since Firefly is mainly used for development, there are default 1
second countdown before running the Operating System. During the 1
second, any input from the debug UART can make the UBOOT enter the
command mode. If you need to set the UBOOT doesn’t enter the command
mode default, you can edit the file:U-boot/include/configs/rk32plat.h
Change the code

   #define CONFIG_BOOTDELAY               1

to

   #define CONFIG_BOOTDELAY               0

Change 0 to 3, then you'll get 3 seconds delay before a normal boot.
Within this duration, press Enter key in the serial console to enter
U-Boot's command line mode.