Actually shorting P8-43 to GND is exactly equivalent to properly pressing the button. However the button is a bit fiddly sometimes, especially with the cape on.
This approach will not be 100% successful, in case a spurious signal is picked up by the SPI device (see here). The proper one (especially on the BeagleBone Green) involves doing this:
giuliomoro Last, I forgot to mention that there are other ways of forcing boot from the SD, e.g.: power on with P8_45 and P8_46 connected to 3.3V and P8_44 grounded. This is relatively easy on a stand-alone Bela, not so much when it's plugged into Salt. There may be easier configurations, too, that may require a single pin to be shorted, which is more doable, but have to double check the Beaglebone's manual.
Still looking for the best approach for the above.
Anyhow, P8_43 to GND is often a good enough solution, especially because normally this is only required once: once you manage to boot from the SD card you then run the
/opt/Bela/bela_bootloader.sh script once and then it should always manage to successfully boot from the SD card in the future.
It is in the release page where you download the image from. Where else would you recommend to put it?