Thursday, August 31, 2006

Optimising for EDTV progressive output

So, I'm finally approaching happiness with the ATI's VGA output. Yes, it's taken me about a fortnight but I guess that's what I expected. I won't go into all of the gory details, but here are some of the more interesting highlights...
  1. Use the Xorg 6.8.2 radeon driver at 852x480@60Hz and digital SPDIF audio: serious ALSA problems on pause/skip/LiveTV channel-change, high CPU usage, video output fairly poor using most de-interlacers, bob deint jumpy. Disable kernel radeon module to avoid kernel Oops.
  2. Use the latest ATI fglrx driver with analogue audio: ALSA problems solved, high CPU usage - no DRM/AGP/DMA, video output fairly poor using most de-interlacers, bob deint jumpy. PQ poor.
  3. Enable AGP in the BIOS! I'd switched it off to save wasting system RAM when I wasn't using the ATI card. Increase videoram from 8-32Mb. Hand-load ati_agp kernel module so that agpgart can handle the ATI IGP chipset.
  4. Enable DRM/AGP (no OpenGL, 3D not supported on IGP with fglrx driver): CPU usage low, bob de-interlacer unusable, kerneldeint ok. Mythfrontend using RTC for video timing. PQ acceptable.
  5. Change output to 856x488@50Hz to match PAL framerate and allow 1:1 screen resolution with overscan: PQ not too bad.
  6. Build and install Xorg 6.9.0 to get OpenGL support for the 9100 IGP; to allow mythfrontend to use OpenGL video sync instead of the RTC fallback method. (FC3 has Xorg 6.8.x). Re-enable loading of the radeon DRI kernel module.
  7. Use Xorg 6.9.0 radeon driver with DRI. agp_ati, agpgart, radeon, drm kernel modules loaded. Mythfrontend now using DRM for video timing. PQ good.
  8. Switch to bob deint: Perfect video timing - no jumping. PQ very good.
I may not be finished yet, but the improvement in audio quality, video quality, CPU usage and display functionality has been dramatic through these steps. Although I was content at step 5 after a week or so of viewing, I feel that step 8 is likely to be a siginificant improvement once I've given it some air-time.

Current Xorg driver config:
Section "Device"
Identifier "onboard"
Driver "radeon"
VendorName "ATI"
BoardName "Radeon 9100 IGP"

Option "AGPMode" "8"
Option "AGPFastWrite" "on"
Option "SubPixelOrder" "RGB"
Option "UseFBDev" "off"
# usually disabled
Option "RenderAccel" "on"
# Usually XAA
#Option "AccelMethod" "EXA"
Option "EnablePageFlip" "on"
Current Modeline:
  ModeLine     "856x488@50" 26.3 856 888 992 1024 488 498 502 513


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