Scaler II vs Scaler problems

Hi Niki,

If the Scaler works in a given design (even with chroma resamplers either side) then it should be possible to just replace the old Scaler (and resamplers) with the Scaler II. Can you give some more information about your datapath and the Scaler II parameter set you are using as I can't see what the problem might be? The loading of coefficients refers only to the polyphase mode and the bilinear mode does not require the user to load coefficients.

With regards the "No blanking in video" option, this is perhaps not as well explained in the docs as it could be. This does refer to the input to the CVI - i.e. you should only turn it on when the input to the CVI has no blanking. When input video has blanking the CVI will have chunks of time where there is no valid output (assuming the input to the next block is ready most of the time). At the end of the input frame the Scaler II will still have a number of output lines left to produce as the lines stored in the internal line buffer flush through. As the last lines of an input frame flush through the line buffer the Scaler II has two choices for what it can do at its input.

1. As the lines of the previous frame flush through the buffer it can wait for lines of the next frame to replace the old lines, thus always keeping the line buffer full with valid data, but only moving data through the buffer and generating valid output when new data is available.

2. Keep the input ready low until the flush has finished, replacing all the input lines with blank data and continuing to generate output data at 'full speed'.

Option 1 is useful if there is no blanking in the input video as there will be no pauses in the valid stream of video reaching the Scaler II. We can wait for new data and consume it immediately without stalling the output. However, the first option will cause underflow at the output if there is blanking (pauses in valid data) at the input between frames as no output data will be produced while we wait for new input data.

Option 2 is sufficient if there is vertical blanking in the input video as this causes a large pause (~40 lines worth) in the input video where there is no valid. Hence dropping the ready while the lines in the buffer flush is not an issue as it will not backpressure anything.

Ideally we might want to use a hybrid third option where we can consume input data from the new frame if and when it arrives, but without ever waiting for it to arrive and stalling the output. Unfortunately the way that the Scaler II is implemented would make this difficult and costly to do. Hence the two options are included separately for the user to choose between at compile time. Indcidentally, the old Scaler used option 2 all the time.

Sorry for the long (and probably poorly worded answer).

Regards,

Kieron