[Openchrome-users] problem on sp8000 with 720x576Noscale

[druyts pascal]

Hello,
I have a problem on an sp8000 with the 720x576Noscale mode when the display 
depth is set to 24. The problem is the same than that described by Robin 
Gilks some months ago. He posted pictures on 
http://gilks.ath.cx/gallery/mythtv

Appart drom mythtv menus, some videos play fine with mplayer, some don't and 
show strange artifact. I think the issue is related to the video original 
resolution.

As a workaround, the problem can be solved by setting the display depth to 
16. The menus and all videos are then dipslyed correctly.

Could this problem be related to memory troughput? What lead me to this 
hypothesis is that I sometimes saw a message in xorg.log telling that the 
memory bandwidth was too small and that therefore, 720x576Noscale was not 
used. I can't provide the exact message, because I can not reproduce it 
anymore. This is only an example of changing behaviour, rebooting the 
machine without changing anything leads to a different behaviour of the X 
server. Another example is that sometimes, for no apparent reason, the dri 
can not initialise. I get an unknown error (999) in the logs. Sometimes also 
xorg complains it could not detect the memory size.

Comming back to memory troughput, I tested it with memtest which shows 
184MB/s. The xorg log shows 221 MiB/s as the best copy with SSE. Those 
figures look small to me as with DDR400 I would expect 1.6GB/s (400Mhz, 32 
bits) and this indeed is the king of figures I get on my backend. Does this 
show I have a problem with the memory (hardware, bios setup?) or is it 
normal for the SP8000? If so, does it show that the frontbus of the SP8000 
is slow and that DDR400 are useless? I could not find any specs for the 
memory bus.

Anyway, a 720x576 image at 25Hz, 3bytes/pixel yields 31MB/s and the measured 
troughput (184MB/s) should be sufficient.

Any idea on the origin of the problem? On the sometimes not reproductible 
behaviour of the X server?

Thanks,

Pascal

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