PB_IN rises to about 900mV. I have no pull ups on this line (I believe that the PMIC has a 100k pull up to an always on power rail).
However I do take the line to GPIO0_26 as an input. I do not recall the default state of that GPIO line so it is possible that that it is being pulled low (not driven low). I'll pull the series resistor to isolate the line and see if it makes any difference....
yes - it has made a difference :-)
PB_IN line now approx at same level as VDD_SYS
my unit has stopped going round a reset loop.
I have a nice and stable 24MHz clock
power rails are all stable
But still no output on serial lines (but that may be because the unit is flashing eMMC - I currently have the Debian flasher image in the UUT's uSD slot.
I'll close this issue off because I'm now looking at a different problem
Many thanks
/Andy