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BOOT_CFG includes many configuration settings. Some of them are particularly important for the boot strategy:
*BT_FUSE_SEL(shipped value = 0)*SDMMC_MFG_DISABLE(shipped value = 0)
*FORCE_INTERNAL_BOOT.
The use of these settings will be more clear soon.
===Serial downloader===
Serial Downloader mode is used to download a Program Image - that is a file that can be executed by the processor - [1] over one of the following connections:
*USB OTG1
*UART1
When this mode is selected, Boot ROM continuously polls for a connection over these interfaces.
It is worth remembering that, when Serial Downloader is enabled, Boot ROM needs to initialize muxing of UART1/UART2 signals as per the following tablestable.{|class="wikitable" style="text-align: center;"|-!Ball name!Ball reference!Signal name!Mux mode|-| UART1_TX_DATA||TBD||uart1.TX_DATA||Alt 0|-| UART1_RX_DATA||TBD||uart1.RX_DATA||Alt 0|-| UART2_TX_DATA||TBD||uart2.TX_DATA||Alt 0|-| UART2_RX_DATA||TBD||uart2.RX_DATA||Alt 0|}
Since these signals can pads may be used to implement different functions other than UART signals in customer's application, '''system integrator needs to verify that the Serial Downloader - if used - is electrically compatible with his/her own carrier board'''.
[1] Program Image includes - but it is not limited to - the code that is executed by the processor when Boot ROM jumps into it.
===Internal boot===
When this mode is selected, Boot ROM tries to retrieve the Program Image from the selected device (NOR flash, NAND flash, SD card etc.).
The selection of the device along with several further device-specific configuration settings can be done in two different ways, depending on BT_FUSE_SEL:
* 0 (shipped value): GPIOs
* 1: eFUSE.
===Typical scenario===
