Weekly Engineering News 36/2008

Andy Green andy at openmoko.com
Wed Sep 10 23:27:27 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| Mike (mwester) wrote:
|> I'll second that sentiment.  Frankly, my impression of the 50633 and
|> Linux is that while the chip might be excellent hardware-wise, it has a
|> serious "impedance mismatch" when it comes to interfacing with the Linux
|> kernel.
| Hmm, not really. Once we can actually do something with it, it's
| a nice chip. The main problem is that its power-up configuration
| cannot be changed according to application needs.

Agreed.  It's hard to get the full scope of that chip but actually it is
a pretty cool device doing a lot of great stuff.

| Oh, Andy, you once suggested for a hypothetical MPU-assisted PMU
| design to put a FET after regulators that could potentially be
| problematic, such as AUTOOUTx -> IO_3V3. A more comprehensive

Don't see why it's problematic other than annoying to blow money on the
MOSFETs needed to correct not having control of PMU bringup.  We just
need the MOSFETs to stagger inrush current.

| solution would place the FET between SYSx and VB_SYS, with
| C1767 on the VB_SYS side, and the MPU on the SYSx side.
| This way, we could control all rails with just one FET.

Hm there is some emergency low VB_SYS volatge state machine transition
into STANDBY or am I imagining it?  Isn't that why we motorboat with bad
VB_SYS?  I am not sure this trick will fly.

| Damn, I really want that MPU.

There is already a device that is asked to do stuff by CPU in GTA03 for
when it is down in suspend... RGB LED controller.  It establishes CPU
offload to something in another power domain, even though that doesn't
seem like MPU in fact that is "degenerate MPU" action already.  So if I
were you I would also keep one eye on expanding that philosophical
foothold.  But for immediate future it's had it I think.

- -Andy
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