update from s-media regarding landscape flicker

Andy Green andy at openmoko.com
Tue Mar 25 13:50:30 CET 2008


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Somebody in the thread at some point said:

>> In portrait, adjacent pixels are in ascending order in memory, so after
>> issuing the address to the DRAM and paying the penalty for random
>> access, prefetch or block fetch modes from the memory work well since
>> you are going to use that data for the next pixels.
> 
> Really bad: if data in video memory is 15bit-packed, and thus not word aligned 
> (hypothetically! i don't believe in this), glamo has to fetch 15bytes per 16 
> pixel in portrait, and 31bytes per 16 pixel in landscape. :-/

No it's 16bpp alright... so "luckily enough" then we only suffer from
the fact it must take >= 4 x 90MHz memory clocks (<= 22.5MW/s bandwidth)
to do random access of pixels we require at 24.5MW/s rate... hm I wonder
what that number of clocks actually is.

- -Andy
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