Andy Green andy at openmoko.com
Wed Aug 20 13:55:35 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| On 8/20/08, Andy Green <andy at openmoko.com> wrote:
|>  We have no control over PMU startup.  It brings up various rails how it
|>  likes all at the same time at levels it likes.
| The PCF50633 ?
| I have printed out the schematics but not committed them to memory yet.

Yes, but the datasheet does not have all the info.  There are various
mask-programmed options on our variant I don't know are listed anywhere
externally.  But the basic deal is it switches on a bunch of regulators
all at the same moment with a high current limit pretty much
guaranteeing major dip in the rail that supplies them, when that rail is
fed from USB with a 500mA limit itself and the battery.  If the battery
isn't "there" enough to support the supply rail (or at all) then the
system fails to start up even.

|>  Problems with startup at low battery (I guess the foot-tangling you
|>  mean) are caused by inrush current limiting also being set too high by
|>  PMU itself and again out of our control because the CPU does not come up
|>  until later.
| foottangling: switching off functions and them staying on. no reaction on
| LowerRight button but the TopLeft still works. And some issues when the
| cpu seems to be idling busy ( tjouchschreen reacts with large delay )

Sounds like userspace world stuff.

|>  These are some of the reasons we would like an always-on MPU to manage
|>  PMU startup in a way we control from the start.
| Would "reeducating" the PMU help?
| ( Will read the complete DS later tonight )
| uwe
| (sorry if I have stepped on someones toes.)

My toes are fine, I just see the makings of a new "LED driver current"
problem here [1] and it needs explaining clearly and quickly before the
lists get filled with "GTA02: testicle microwave in your pocket even
when it is off?"  If there's a real problem we have to know but equally
if the problem is "unreal" or "theoretical-only" that needs pointing out

Additionally some months ago various people in Openmoko did not
understand these reasons to have an MPU to manage the system and
rejected the idea.  Since not having any "always-on intelligence" blew
up in our faces with the low battery issue I guess it will have an
easier ride next time.

- -Andy

[1] Previously LED driver had a problem it ate some tens of mA due to
bad design when the LED was on.  The LEDs are very seldom on, but there
was all kinds of hysteria on user lists that went on for some time.
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