Original post -> https://www.raspberrypi.org/forums/viewtopic.php?t=191197
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/gpio.md
https://github.com/raspberrypi/usbboot
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/host.md
This can explain how to change setting program_usb_boot_mode=1 using gpio pins
- The individual OTP bits/fuses, when set disable a certain booting source, regardless of any associated boot source GPIO## wiring? Argh, only now I'm understanding that terse note "note this cannot enable boot modes that have not already been enabled in the OTP" in the documentation; this may be misleading as the OTP rather disables, or am I mistaken here?
- When a certain OTP isn't set, then a corresponding GPIO## level does enable or disable a certain booting source? Do I need to pull up or down, and which resistance to Vcc or GND will be needed?
- How is the GPIO## mapping exactly?
- GPIO22: boot from primary SD
- GPIO23: boot from secondary SD
- GPIO24: boot from NAND
- GPIO25: boot from SPI
- GPIO26: boot from USB mass storage device
https://www.raspberrypi.org/forums/viewtopic.php?t=175761
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