3
Contents
1. Conventions used in this manual ................................................ 5
2. Acronyms and Abbreviations ...................................................... 6
3. Introduction ................................................................................... 7
3.1 What is a boot loader? .............................................................................................................. 7
3.2 What is U-Boot? ........................................................................................................................ 7
3.3 Features of U-Boot .................................................................................................................... 7
3.3.1 Customizable footprint ...................................................................................................................... 7
3.3.2 Monitor .............................................................................................................................................. 7
3.3.3 Variables ........................................................................................................................................... 8
3.3.4 Ethernet and USB ............................................................................................................................. 8
3.3.5 Numbers ........................................................................................................................................... 8
3.4 The boot process ...................................................................................................................... 8
4. U-Boot commands ........................................................................ 9
4.1 Overview ................................................................................................................................... 9
4.2 Built-in commands ..................................................................................................................... 9
4.2.1 Information commands ................................................................................................................... 10
4.2.2 MII commands ................................................................................................................................ 11
4.2.3 Network commands ........................................................................................................................ 11
4.2.4 Memory commands ........................................................................................................................ 12
4.2.5 Serial port commands ..................................................................................................................... 12
4.2.6 Environment variables commands .................................................................................................. 13
5. Environment variables ............................................................... 14
5.1 Overview .................................................................................................................................14
5.2 Simple and recursive variables ...............................................................................................14
5.3 Scripts .....................................................................................................................................14
5.4 System variables .....................................................................................................................15
5.4.1 Common system variables .............................................................................................................. 15
5.4.2 Network related variables ............................................................................................................... 16
5.4.3 Dynamic variables .......................................................................................................................... 16
5.4.4 User keys ........................................................................................................................................ 17
5.4.5 Protected variables ......................................................................................................................... 17
6. Network interfaces ...................................................................... 18
6.1 Number of interfaces ...............................................................................................................18
6.2 Primary network interface .......................................................................................................18
6.3 Active network interface ..........................................................................................................18
7. Bootscript .................................................................................... 19
7.1 Bootscript process ...................................................................................................................19
7.2 Creating a bootscript ...............................................................................................................19
7.2.1 Creating a bootscript in Windows ................................................................................................... 20
7.3 Configuration for launching the bootscript ..............................................................................20
7.4 Bootscript restrictions ..............................................................................................................20
8. Boot commands .......................................................................... 21
8.1 Overview .................................................................................................................................21
8.2 Reading images into RAM ......................................................................................................21
8.2.1 From Ethernet ................................................................................................................................. 21
8.2.2 From SD/MMC card ........................................................................................................................ 21
8.2.3 From flash ....................................................................................................................................... 22
8.3 Booting images in RAM...........................................................................................................22
8.4 Direct booting ..........................................................................................................................22
