View source for CM-T3530: U-Boot: Firmware Overview

CM-T3530 firmware consists of two components: X-Loader and U-Boot. X-Loader is the bootstrap utility invoked by the boot ROM code of OMAP35x processor. X-Loader performs minimal hardware initialization and loads stage two bootloader, namely U-Boot. U-Boot initializes hardware modules necessary for system boot and loads the operating system.

== X-Loader ==
X-Loader should reside in the first erase block of the system NAND flash or in a file on MMC/SD card. It is loaded into OMAP35x internal SRAM immediately after system reset. The OMAP35x internal boot ROM determines what storage media to use in accordance with BOOT_SOURCE signal value (pin 65 of connector P1 on CM-T3530). SB-T35 allows easy switch between NAND and MMC/SD boot.

X-Loader is responsible for initial clock setup, DDR initialization and boot media controller initialization. After basic hardware setup X-Loader loads U-Boot bootloader into the system RAM and transfers control to the U-Boot bootloader.

== U-Boot ==
U-Boot is the stage two bootloader used on CM-T3530. It allows flexible selection of operating system boot modes, provides scripting facilities and command line interface through serial port.

U-Boot should reside in the system NAND flash starting from offset 0x80000. In addition, two blocks at offset 0x260000 are used by the U-Boot environment. In case an MMC/SD card is used as boot media, U-Boot binary should be present in card's root directory and named {{filename|u-boot.bin}}.

U-Boot allows booting operating system from the on-board NAND flash, MMC/SD card or from network.
Please consult [[U-Boot quick reference]] and [http://www.denx.de/wiki/U-Boot/Documentation U-Boot project documentation] for U-Boot features and commands description.

== Boot sources ==
CM-T3530 can boot either from on-board NAND flash or from MMC/SD card. The boot source can be selected using jumper E6 or button SW1 on SB-T35.
* To boot the system from the on-board NAND flash make sure that jumper E6 is not present.
* To boot the system from the MMC/SD card install jumper E6 before power-on or hold button SW1 during system startup.
Please refer to [[CM-T3530: Linux: Booting from MMC/SD card]] for further details.

== Default NAND flash mapping ==
{| cellpadding="3" border="1" style="border: 1px solid rgb(85, 85, 85); border-collapse: collapse;"
|+ CM-T3530 NAND flash mapping
|-
! Offset
! Description
! Size (kilobytes)
|-
| 0x0
| X-Loader
| 512
|-
| 0x80000
| U-Boot
| 640
|-
| 0x12000
| Reserved  
| 1280
|-
| 0x260000
| U-Boot environment
| 256
|-
| 0x2a0000
| Linux kernel
| 4096
|-
| 0x6a0000
| Linux filesystem
| remaining NAND flash space
|}

== Know issues ==
* If U-Boot environment variable {{parameter|bootdelay}} is set to 0 or an invalid value, automatic OS boot cannot be stopped.

[[Category:U-Boot|Firmware Overview]]
[[Category:CM-T3530|U-Boot: Firmware Overview]]