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<section begin=History/>
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* reads the mode pins to determine the primary boot device
* once it is satisfied, it executes the boot code
== Boot options ==
Two options are available related to system boot. They are identified by the Boot field of the ordering code as follows:
* 0: SPI NOR eMMC / SD option (SOM code: DXLxxxx0xxR???)* 1: NAND / SD option (SOM code: DXLxxxx1xxR???)
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 eMMC / SD option ===
Selection of primary boot device is determined by the BOOT_MODE_SEL signal as follows:
* BOOT_MODE_SEL = 0
** primary boot device is SD1SD2 (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 eMMC connected to eCSPI1USDHC1** in case no valid image is found in NOR flashon eMMC, boot ROM shall enable USB serial download mode automatically
=== NAND / SD option ===
Selection of primary boot device is determined by the BOOT_MODE_SEL signal as follows:
* BOOT_MODE_SEL = 0
** primary boot device is SD1SD2 (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
** in case no valid image is found in NAND flash, boot ROM shall enable USB serial download mode automatically
===Important note for DualLite/Solo based products (''manufacture mode'' management)===When Dual Lite or Solo processor are 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 detect SD/MMC card on USDHC2 port. If a card is inserted, ROM will try to boot from it. SD2_CD_B is used, GPIO_1 and GPIO_4 signals as card detect signal during bootrom's ''manufacture mode''. This signal need to be kept high during bootstrap stage in order 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). Please note that, in case GPIO_1 signal is used to implement [[Reset_scheme_(AxelLite)#Handling_CPU-initiated_software_reset|software reset circuit]], it is high during bootstrap stage by design.
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[[Category:MITO 8M]]