arm 7 & arm 9 microcontrollers at91 1 at91rm9200 boot strategies

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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AT91RM9200 Boot strategies

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Boot strategies• BMS allows AT91RM9200 to boot from two different sources

Embedded boot ROM (BMS high) Boot program which integrates

Bootloader Uploader

Flash Primary bootstrap and de-compression code are run in the flash De-compression code de-compresses Uboot in SDRAM and jumps to it. (see Uboot slides)

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Boot program• Boot program features

Default boot program stored in ROM-based products Downloads and runs application from external storage media into SRAM Automatic detection of valid application support a wide range of non-volatile memories

SPI Dataflash TWI EEPROM 8-bit parallel memories through EBI

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Boot flow chart

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Bootloader• Bootloader starts by looking for a valid program in the off-chip non-volatile memories

Dataflash through SPI EEPROM through TWI 8-bit memory device through EBI

Uploader

Valid program foundNo Yes

Program is loaded in SRAM and executed by branching at 0x0000_0000 after remap

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Vector analysis • Bootloader checks the first 32 bytes of the ARM exception vector. These bytes should implement

A branch A load PC with PC relative addressing

• The sixth vector structure

Nb of 512 bytes blocks to download

ReservedNumber of pages

Dataflash page size

31 17 16 13 12 8 7 0

• The user must replace the sixth vector by its own vector

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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SRAM remap• After reset, the code in internal ROM is mapped at both addresses 0x0000_0000 and 0x0010_0000 • Remap action is performed after download completion

Internal SRAM

Internal ROM

Internal ROM

Internal SRAM

0x0020_0000

0x0000_0000 0x0000_0000

0x0010_0000Remap

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Uploader• The boot Uploader performs the DFU and Xmodem transfer to upload the application in SRAM at address 0x0020_0000 • DBGU Serial Port

Uploader initializes the DBGU serial port at 115200,8,n,1 The application is downloaded through Xmodem protocol The size of the application should be less than SRAM size (3KB)

• DFU : Device Firmware Upgrade DFU protocol allows the firmware update of USB devices The application is downloaded in SRAM at address 0x0020_0000

• The Application’s size should be less than SRAM size (3KB)

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Xmodem protocol• The DBGU sends character ‘C’ to start an Xmodem protocol• The Xmodem protocol supported is the 128-byte long block• Xmodem protocol uses two character CRC-16 to detect a maximum of bit error

Host device

C

SOH 01 FE Data[128] CRC CRC

ACK

SOH 02 FD Data[128] CRC CRC

ACK

SOH 03 FC Data[100] CRC CRC

ACK

EOT

ACK

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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DFU protocol• DFU protocol upgrades firmware through USB devices • A 48 MHz USB clock is set during the device initialization

Host device

Prepare for an upgrade

USB reset

DFU mode activated

Download this firmware

Prepare to exit DFU mode

USB reset

Firmware execution

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Boot program limitations• The download code must be less than the SRAM size 3KB• The EEPROM device address must be 0 on the TWI bus• The code is always downloaded from device address 0x0000_0000 to the address 0x0000_0000 of the SRAM after remap• The downloaded code must be position-independent or linked at address 0x0000_0000.

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Boot solutions • U-Boot overview

Standalone software that initializes AT91RM92000 processor and displays a prompt for an interactive mode The user is prompted to enter commands It offers a set of commands that allows to do :

Read/modify memory areas

Set environmental variables

Download data from serial port or from Ethernet interface

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Uboot Layers • U-Boot is made of two programs that reside in the flash

Boot image Primary bootstrap De-compression executable

U-Boot gzipped image

Boot image24 KBytes

Free

Environment variables 8Kbytes

U-Boot gzippedimage

64 KBytes

0x10000000

0x10006000

0x1000E000

0x10010000

0x10020000

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Uboot Launching sequence

Primary bootstrap(Assembly code)

Starts high-speed clocks for CPU

Programs the on-chip memory controller to define the memory layout

De-compression

De-compresses U-Boot in RAMand jumps to it

U-Boot

U-Boot Running

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ARM 7 & ARM 9 MICROCONTROLLERSAT91

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Boot solutions • U-Boot features

Standalone primary boot OS independent Autoboot and interactive mode Command line interface Non volatile environmental variables Flash programming capability Download through serial port (Kermit protocol) Download through Ethernet (tftp) Scripting capability