GSM flow-control non-functional on GTA01 (and possibly GTA02)

Andy Green andy at
Mon Apr 28 16:47:29 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| Andy Green wrote:
| ...
|> In practical terms, FIQ on S3C24xx works that you can cherrypick ONE
|> normal interrupt source and elevate it to "FIQ power"...
| This problem may well exist on the GTA02 as well (although it has a
| deeper FIFO, I suspect that will only serve to mask the problem so that
| in accordance with Murphy's law, it will happen only when correct
| operation is most needed).  Does the fact that the GTA02 already uses
| the FIQ preclude this solution for that device as well, or is there some
| other consideration for shared FIQ use?

The S3C2442 datasheet has a big NOTE by that register saying to only
enable one source.  I guess the issue is that the ARM can't deal with
FIQ reentrancy, it has a single set of FIQ shadow registers for high
speed context switching: once you started using them if another FIQ
comes you are in trouble.

If I understood it the problem only comes during resume... I guess the
big question is, is all that is needed to make the problem a long period
with interrupts off?  If that's all it takes, I would wonder if one of
the resume handlers is spinning at a bad time, eg, LCM ASIC one has
mdelay() in there IIRC.

- -Andy
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