AT91Bootstrap is a first step bootloader providing a set of algorithms to manage hardware initialization (GPIO, Clock, SDRAM, etc), to download your main application from specified FLASH media to main memory and to start it.
In the linux4SAM pre-built demo it is used to configure the hardware and to load and start the standard
U-Boot bootloader, it can also be configured to start directly the linux kernel.
This section describes How to load
AT91Bootstrap into the boot media with
SAM-BA.
- Connect the USB Device Interface to your host machine using the USB Device Cable
- Make sure that the chip can execute the bootROM monitor SAM-BA-boot :
- Start SAM-BA GUI Application
- Select the the board in the drop-down menu and choose the USB Connection
- Eventually plug back a jumper to access the media on which u-boot must be loaded to
- In the main SAM-BA window :
- Choose the proper media tab (DataFlash, NandFlash, etc.) in the SAM-BA GUI interface
- Initialize the media choosing the Enable action in the Scripts rolling menu and press Execute
- Choose Send boot file, press Execute
- Select the at91bootstrap binary file and press Open ; the media is written down
- Close SAM-BA, remove the USB cable
AT91 chips embed a boot ROM code. It is enabled depending on BMS (Boot Mode Select) pin state on reset.
This ROM code scans the contents of different media like SPI DATAFLASH, NAND FLASH or SDCARD to determine if a valid application is available then it download the application into SAM9 internal SRAM and run it.
To determine if a valid application is present the ROM code checks the eight ARM exception vectors.
If no application is available then SAM-BA application is executed. It waits for transactions either on the USB device, or on the DBGU serial port, Then the
SAM-BA tool can be used to program FLASH or EEPROM present on your board.
For more information on this topic, please check the corresponding SAM product datasheet section
Boot Program . You can find a valuable summary in the document named
SAM9 Boot Strategies or see the cross matrix below..
ROM Code boot Sequence example
Boot capabilities matrix
Here is :
a summary of the boot feature available for each board (re-compilation needed)
the solution chosen for the Linux4SAM pre-built binaries.
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| Product |
Boot from
DataFlash (SPI0 CS0) |
Boot from
DataFlash (SPI0 CS1) |
Boot from
NAND Flash |
Boot from
SD card |
Boot from
NOR Flash |
Boot from
Internal Flash |
| at91sam9260ek |
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| at91sam9xeek |
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| at91sam9261ek |
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| at91sam9263ek |
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| at91sam9rlek |
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| at91sam9g20ek |
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| at91sam9g10ek |
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| at91sam9g45ekes |
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| at91sam9m10ekes |
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| at91sam9m10g45ek |
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The Dataflash version of
AT91Bootstrap (version 1.10 or older) will load a second level bootloader or application from the address
0x8000.
Dataflash memories have page size of 1056 bytes, (0x420 hex) and the load address 0x8000 is thus in the middle of a page.
Newer version of
AT91Bootstrap (from version 1.11) will load a second level bootloader or application from the address
0x8400.
In brief
To compile an
AT91Bootstrap project:
- go into the board directory
- select your board by going into the corresponding board directory
- select your media by going into the corresponding directory
- run make
Example:
To compile a DataFlash boot project for AT91SAM9260-EK board, type the following commands:
cd board/at91sam9260ek/dataflash
make clean
and
make
or if you want to specify the cross-compiler :
make CROSS_COMPILE=<path_to_cross-compiler/cross-compiler-prefix->
path_to_cross-compiler is only needed if it is not in your
PATH.
Usually
cross-compiler-prefix- looks like
arm-linux- or
arm-elf-
Notes
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