If I set up to boot a pi3 from usb can I revert to sd slot boot later? This is in reference to the new OTP bit procedure
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1What new OTP procedure?– Steve RobillardJul 8, 2017 at 2:54
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raspberrypi.org/forums/viewtopic.php?f=29&t=159691– Walter SteenJul 9, 2017 at 11:14
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The link is about the One Time Programmable Memory in the boot code of the Pi3 that allows USB drive to boot at power on. The link seems to imply that the boot will look for the slot, then check OTP bit and boot from USB device. Google raspi otp– Walter SteenJul 9, 2017 at 11:23
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2 Answers
From Raspberry Pi Documentation:
"The flow of boot begins with reading the OTP to decide on the valid boot modes enabled. By default, this is SD card boot followed by USB device boot. Subsequently, the boot ROM checks to see if the GPIO boot mode OTP bits have been programmed — one to enable GPIO boot mode and one to select the bank of GPIOs it uses to disable boot modes (low = GPIOs 22-26, high = GPIOs 39-43). This makes it possible to use a hardware switch to choose between different boot modes if there is more than one available."
As per above, it doesn't seem that you need to program the OTP (One Time Programmable) bits to boot from USB.
answered Jan 8, 2018 at 23:27
Actually you do not need to "revert" from anything. The SD / TF slot will be still functioning as usual.
The OTP procedure will allow other boot options ( read: USB ) but it is AND, not OR.
SoC checks bootcode.bin on the SD card first. If not find proceed to USB.
So basically just taking out the USB and putting a TF in the slot will make the pi boot as usual.
