Selecting the Boot Mode
The block diagram should also indicate which interface will be used for booting this device.
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These devices contain an on-chip ROM Bootloader:
- The boot config pins are sampled at power-on-reset
- Sets up system for boot depending on boot configuration selected
- Depending on boot mode, copies image to internal RAM and then executes it
- Maximum size of the boot image is 128KBytes
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The following boot modes are supported:
- NOR Flash boot
- NAND Flash boot
- SPI boot
- SD/MMC boot
- EMAC boot
- UART boot
- USB boot (like an ethernet card, not as mass storage)
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If the first boot source fails to boot, the ROM will move on to the next one in the sequence. Keep in mind that some boot sources take some time to timeout if that boot source isn’t available.
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Read AM335x Technical Reference Manual Initialization Chapter to understand details on different boot modes
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Key Boot Considerations:
- It is recommended to include population options for other boot modes to aid in development
- Boot pins have other functions after reset. Make sure your board design takes this into account when choosing pullup/down resistors for the boot pins.
參考文章
例子：參考BBB板的啓動方式 BBB_SCH.PDF的設計(https://github.com/CircuitCo/BeagleBone-Black)