:-)
Back in March, there was in interesting discussion in the list about scaling on the 150/500's between Sergey, Tyler, and Chris about scaling, referenced here:
http://www.gossamer-threads.com/lists/ivtv/devel/18652?search_string=cx25840%20observations%2C%20scaling;#18652
Sergey postulates that, in order to make scaling work properly, HACTIVE and VACTIVE need to be set in addition to HSCALE and VSCALE, but that HACTIVE and VACTIVE are being reset (somewhere) to full mode, resulting in the final image being cropped instead of scaled.
If that is so, reading through the 'Autoconfiguration Defaults' section of the datasheets referenced in that discussion, it appears that HACTIVE and VACTIVE are both reset by the autoconfiguration logic whenever a mode is changed or a signal is detected by hardware. The default values (for NTSC) are 720 (hex 2D0) for HACTIVE and 503 (hex 1E7) for VACTIVE.
To quote from the 'Autoconfiguration Parameters' section:
> Autoconfiguration Parameters
> The user can write the following registers, or allow them to be set automatically
> based on either the specified or detected video format. The user can also let the
> hardware configure these registers based on the video format, and overwrite
> selected parameters to customize the mode.
> If the ACFG_DIS bit (MODE_CTRL) is left cleared, the hardware will set these
> registers when either of the following happens:
> The user specifies a specific mode by writing the VID_FMT_SEL
> (MODE_CTRL) field.
> The user specifies the autodetect mode in the VID_FMT_SEL (MOD_CTRL)
> field, and the autodetect hardware detects a mode change.
> When the ACFG_DIS bit is set, the hardware will never modify the values written
> by the programmer to these registers
Although I may very well have missed it, I haven't found any place where the autodetect mode is disabled. Wouldn't this mean that at the start of every recording, when the signal hits the decoder and the decoder detects the mode, that HACTIVE and VACTIVE end up being reset to their default values?
No doubt I have missed something really important. Please feel free to correct or ignore me as you prefer.
Bill
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