AURA SOM/AURA Hardware/Power and Reset/System boot
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Contents
System boot[edit | edit source]
The boot process begins at Power On Reset (POR) where the hardware reset logic forces the ARM core to begin execution starting from the on-chip boot ROM. The boot ROM:
- determines whether the boot is secure or non-secure
- performs some initialization of the system and clean-ups
- reads the mode pins to determine the primary boot device
- once it is satisfied, it executes the boot code
Boot options[edit | edit source]
Two options are available related to system boot. They are identified by the Boot field of the ordering code as follows:
- 0: SPI NOR / SD option (SOM code: DAUxxx0xxxxR)
- 1: eMMC / SD option (SOM code: DAUxxx2xxxxR)
- 2: SPI NAND / SD option (SOM code: DAUxxx1xxxxR)
For both options the selection of primary boot device is determined by the BOOT_MODE_SEL signal as described in the following sections. BOOT_MODE_SEL is latched when processor reset is released.
In any case, boot process is managed by on-chip boot ROM code that is described in detail in processor's Reference Manual.
SPI NOR / SD option[edit | edit source]
Selection of primary boot device is determined by the BOOT_MODE_SEL signal as follows:
- BOOT_MODE_SEL = 0
- primary boot device is SD2 (USDHC2)
- boot ROM will try to boot a valid image from the SD card first, and then from the SPI NOR. In case no valid image is found, boot ROM shall enable USB serial download mode automatically
- BOOT_MODE_SEL = 1 or floating
- primary boot device is SPI NOR flash connected to FLEXSPI
- in case no valid image is found in SPI NOR flash, boot ROM shall enable USB serial download mode automatically
eMMC / SD option[edit | edit source]
Selection of primary boot device is determined by the BOOT_MODE_SEL signal as follows:
- BOOT_MODE_SEL = 0
- primary boot device is SD2 (USDHC2)
- in case no valid image is found in SD card, boot ROM shall enable USB serial download mode automatically
- BOOT_MODE_SEL = 1 or floating
- primary boot device is eMMC connected to USDHC1
- in case no valid image is found in eMMC flash, boot ROM shall enable USB serial download mode automatically
SPI NAND / SD option[edit | edit source]
Selection of primary boot device is determined by the BOOT_MODE_SEL signal as follows:
- BOOT_MODE_SEL = 0
- primary boot device is SD2 (USDHC2)
- in case no valid image is found in SD card, boot ROM shall enable USB serial download mode automatically
- BOOT_MODE_SEL = 1 or floating
- primary boot device is SPI NAND flash connected to FLEXSPI
- in case no valid image is found in SPI NAND flash, boot ROM shall enable USB serial download mode automatically
Important note for manufacture mode management[edit | edit source]
When the internal boot and recover boot (if enabled) failed, the boot goes to the SD/MMC manufacture mode before the serial download mode.
By default, the SD/MMC manufacture mode is enabled. DAVE Embedded Systems do not blow the fuse of the DISABLE_SDMMC_MFG in order to disable it.
Boot ROM detects SD/MMC card on USDHC2 port. If a card is inserted, ROM will try to boot from it. SD2_CD_B is used as card detect signal during bootrom's manufacture mode. This signal need to be kept high during bootstrap stage to prevent the intervention of bootrom's manufacture mode, if it's not desidered.
Bootstrap stage has to be intended as the time elapsing between the release of hardware reset (CPU_PORn) and the execution of the first instruction of user code (typically this is the reset vector of U-Boot boot loader).
