Wifi / PMU Startup actions enforced by our variant
andy at openmoko.com
Wed Aug 20 22:38:55 CEST 2008
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Somebody in the thread at some point said:
| On 8/20/08, Andy Green <andy at openmoko.com> wrote:
|> 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.
| Explains a bit why the batlevel is a jojo.
| Is that supplemental info available somewhere?
| The sensible thing to do is raise a minimal system and then
| power up units one by one. Isn't ARM fully static?
| i.e. could i have the cpu running from rom and some sram
| in bits and bouts when "switched off"?
| I'le read up a bit and then come back to you if I have a good idea.
Good ideas are always welcome.
Basically our PMU variant 04/N3 brings up a bunch of stuff in activation
phase 3 all together:
~ - AUTO -> 3.3V ON 400mA current limit on startup only
~ - DOWN1 -> 1.2V ON 390mA current limit on startup only
~ - DOWN2 -> 1.8V ON 390mA current limit on startup only
~ - LDO1 -> 2.8V ON (motion sensor power)
~ - LDO4 -> 2.8V ON (bluetooth)
~ - LDO6 -> 3.0V ON (LCM)
There are various other settings forced, notably USB current limit is
set to 500mA.
There is no choice about that lot. You get nothing or all of those
coming on at the same moment. There is no smarts in the PMU.
Because the CPU operation is dependent on AUTO / DOWN1 / DOWN2, it is
meaningless to talk about CPU controlling PMU startup. CPU is not able
to do anything until some time after PMU has completed its startup
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