AURA SOM/AURA Hardware/Power and Reset/System boot
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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 OTP settings
- reads the mode pins to determine the primary boot device
- once it is satisfied, it executes the boot code
Boot options[edit | edit source]
The default primary boot device is defined at the factory and identified by the Boot Mode fileld of the ordering code as follows:
- 0: SPI NOR / SD option (SOM code: DAUxxx0xxxxR)
- 1: eMMC / SD option (SOM code: DAUxxx1xxxxR)
- 2: SPI NAND / SD option (SOM code: DAUxxx2xxxxR)
For both options an alternative primary boot from SD/MMC card is provided, selectable by driving low the BOOT_MODE_SEL signal. Bootable SD/MMC card connects via the SD2 (USDHC2) bus.
All boot modes provide 'single boot' mode, that is the Cortex-A55 ROM loads all containers and images.
If primary boot fail TBD
| Ordering code 'Boot Mode' fileld | BOOT_MODE_SEL | Primary boot device | Secondary boot device (if failed primary) |
|---|---|---|---|
| 0 | 0 | SD/MMC card on USDHC2 | |
| 1 | FlexSPI NOR on FLEXSPI1 | ||
| 1 | 0 | SD/MMC card on USDHC2 | |
| 1 | eMMC on USDHC1 | ||
| 2 | 0 | SD/MMC card on USDHC2 | |
| 1 | FlexSPI NAND on FLEXSPI1 |
BOOT_MODE_SEL is latched when processor reset is released.
The iMX93x SoC uses some GPIOs to read the boot configuration set on the SOM: for this reason the SOM's ports UART1_TXD, UART2_TXD, SAI1_TXFS and SAI1_TXD0 are floating (high impedance) while CPU_PORn signal is low.
- in case no valid image is found in XXXXX, 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).
