Getting Started

Introduction

This page is a starting point for the Linux4SAM offer and allows you to easily get a running embedded Linux distribution on AT91 products.

This Getting started describes also how a Linux4SAM system boots and how binaries are installed on FLASH memories. For each topic a more detailed section exists with in-depth description, valuables web links, source code how to rebuild used binaries.

Boot sequence

Several pieces of software are involved to boot a linux kernel on SAM9 products. First is the ROM code which is in charge to check if a valid application is present on supported media (FLASH, DATAFLASH, NANDFLASH, SDCARD).

The boot sequence of linux4SAM is done in several steps :

1. Boot Program - Check if a valid application is present in FLASH and if it is the case download it into internal SRAM.
   For more information on this topic, please check the Boot strategies section and particularly the Boot capabilities matrix.
2. AT91Bootstrap - In charge of hardware configuration, download U-Boot binary frome FLASH to SDRAM, start the bootloader
3. U-Boot - The bootloader, in charge of download kernel binaries from FLASH, network, USB key, etc. Start the kernel.
4. Linux kernel - The operating system kernel.
5. Root Filesystem - Contains applications which are executed on the target, using the OS kernel services.

1. Processor comes out of reset and branches to the ROM startup code.
2. The ROM startup code initializes the CPU and memory controller, performing only minimal initialization of on-chip devices, such as the console serial port to provide boot diagnostic messages. It also sets up the memory map for the kernel to use in a format that is consistent across platforms, and then jumps to the boot loader.
3. The boot loader decompresses the kernel into RAM, and jumps to it.
4. The kernel sets up the caches, initializes each of the hardware devices via the init function in each driver, mounts the root filesystem and execs the init process, which is the ultimate parent of all user mode processes, typically /sbin/initd.
5. Executing the first program linked against the shared C runtime library (often init) causes the shared runtime library to be loaded. In a typical Linux system, init reads /etc/inittab to execute the appropriate run control script from /etc/rc.d, which execute the start scripts to initialize networking and other system services

Linux4SAM DataFlash demo - Memory map

* : On AT91 chips with embedded FLASH ¹, AT91Bootstrap is located into the internal FLASH and not in the DataFlash nor NandFlash.

Linux4SAM NandFlash demo - Memory map

* : On AT91 chips with embedded FLASH ¹, AT91Bootstrap is located into the internal FLASH and not in the DataFlash nor NandFlash.

Requirements

Hardware

• a Windows XP host (or above) to run the SAM-BA tool ;
• power supply stocked with the Evaluation Kit ;
• USB Device Cable ;
• serial Cross Cable (Female-Female) ;
• eventually a DataFlash Card => check Boot capabilities matrix (for AT91SAM9263-EK for example) ;
• AT91SAM9-EK Evaluation Kit. Check below how kits look like and how to connect them :

AT91SAM9260-EK	AT91SAM9261-EK	AT91SAM9263-EK (REV-A)
AT91SAM9XE-EK	AT91SAM9RL-EK	AT91SAM9263-EK (REV-B) 2

Software

• a serial terminal emulator (HyperTerminal, minicom, etc.) :

Serial communication parameters 115200 8-N-1 :

• AT91 ISP 1.10 (or higher) ; containing the SAM-BA tool => Check the SoftwareTools page ;
• the demo archive provide just below. This archive contains :
  • all 4 components binaries : AT91Bootstrap, u-boot, Linux kernel, root filesystem ;
  • a TCL/SAM-BA script that interfaces with the SAM-BA tool to flash the demo ;
  • a .bat script able to run the flashing script calling SAM-BA itself.

Flashing a demo on AT91 boards

Before flashing the demo, make sure that you have installed the SAM-BA tool on your host computer.

• connect a USB cable on the board
• connect a serial link on DBGU connector and open the terminal emulator program
• choose the proper procedure depending on your chip through the following table :

• launch the proper .bat file : this script will run SAM-BA with proper parameters
• when the programmation logfile.log appears (this will take a few minutes), remove the USB cable
• power cycle the board
• look the system booting on the LCD screen or trough the serial line
• calibrate accurately the LCD screen (if needed)

Playing with the demo

Ok, now you should have the Linux demo up'n running on your board ! Have a walk through applications of this demo.

Going Forward

If you want to rebuild this demo from sources, go through each component topic and you will have a comprehensive explanation of it role and how to build it.

For people in a hurry, there is a summary page which collects all material to build from sources : it allows you GoingForward quickly.

Notes

1: Embedded FLASH available on AT91SAM9XE for instance.

2: AT91SAM9263 MRLA or MRLB could be soldered on this board revision. To identity which chip revision you have, check AT91SAM9263-EK user guide at http://atmel.com/dyn/products/tools_card.asp?tool_id=4057

3: Touchscreen driver not available yet ; check LinuxKernel#2_6_24_at91_exp_patch