tigernero wrote: ↑
Fri Aug 16, 2019 4:40 pm
exact the page to which I referred was the one taken from the raspberry site documentation, this:
https://www.raspberrypi.org/documentati ... des/msd.md
in which it is written:
"The Raspberry Pi 3A + and 3B + are able to boot from USB without any changes"
this is not true for the pi3a + so I had to set otp number 17 with the command
"echo program_usb_boot_mode=1 | sudo tee -a /boot/config.txt"
Things get a little complicated around USB boot - there are two modes:
USB device mode boot
USB host mode boot
That page talks about USB mass storage boot, which is enabled by USB host mode boot, but unfortunately the option to enable USB host mode boot by programming an OTP bit is called program_usb_boot: that option has no effect on the ability of the Pi to use USB device mode boot.
So the page needs to have the following information added:
1. On the Pi 3A+, setting the OTP bit to enable USB host mode boot will prevent that Pi 3A+ from doing USB device mode boot, due to the fact that all Pi 3A+'s have the OTG_ID pin tied to ground. See https://www.raspberrypi.org/forums/view ... 4#p1392654
. All but a few thousand early Pi 3A+'s have the USB host mode boot bit UNSET - yours being one with it UNSET.
2. The page needs to correctly distinguish between USB host boot mode and USB device boot mode, which is does not at present. ("The Raspberry Pi 3A + and 3B + are able to boot from USB without any changes" is meant to refer to HOST mode only).
3. It should also mention that the option to enable USB host mode boot, by setting a bit in the OTP, is misnamed in a potentially misleading way.
4. The correct sentence from 2 above would be "The Raspberry Pi 3A + and 3B + are able to use USB host mode boot without any changes", which as you point out is wrong, since all but a few early Pi 3A+'s have the USB host mode boot bit UNSET. So that should read "The Raspberry 3B+ is able to use USB host mode boot without any changes".