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YPbPr 1080i TV output limitations (Robin)

 
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The Robin Z5xx module features a Chrontel CH7022 which provides a component YPbPr HDTV capable output. This articel describes the current limitations with the interlaced 1920x1080 output format.

Background

The Chrontel CH7022 can be configured to output the video signal as VGA, Component, S-Video or Composite YPbPr signals. For more information how to configure the IEGD video driver to force the Chrontel CH7022 to output YPbPr signals, please read the wiki page: Component TV output YPrPb (Robin). The YPbPr output can be set to different TV standards (e.g. 576i50, 480i60, 720p50 or 1080i50) . This output setting is independent of the screen resolution setting in the OS. You can for example set the video output to 720p50 (which is a resolution of 1280x720) and have the OS set to a higher or lower resolution. If the resolution setting in the OS is not native, the Chrontel CH7022 down or up scales the video signals. If the video output is set to an interlaced format, the CH7020 converts a progressive scanned signal into an interlaced. For this conversion, the CH7022 needs a line buffer. This buffer can handle up to 1704 pixels per line. This means any input format that has more than 1704 pixels per line has to bypass the scaling engine. Unfortunately, the current IEGD and EMGD driver for the US15W does not provide interlaced outputs to the CH7022.

Affected Settings

If the Video output is set to any interlaced 1920x1080 format (e.g. 1080i50, 1080i59 or 1080i60), the native OS resolution of 1920x1080 can not be used.

Settings that are working without any Problem

  • All progressive scanned output formats are working without any problem. For example, if the output is set to 1080p50, the native OS resolution of 1920x1080is working without any problems. Also progressive 1280x720 HDTV resolutions are working without limitation
  • All interlaced output formats (e.g. 1080i50, 576i50 etc) are working with all OS resolutions that have lower horizontal resolution than 1704 pixels (e.g. 1600x1200)
  • The VGA, Composite and S-Video output of the Chrontel CH7022 are not affected

Current State of the Issue

Toradex has placed a feature request to the Intel Development Team of the EMGD driver. It requests the option for a interlaced output of the US15W graphic engine in order to bypass the CH7022 scaling engine. If you are interested to get updates on the feature request state, please write an email to robin@toradex.com