User guide

Chapter 22: Scaler II MegaCore Function 22–3
Functional Description
January 2013 User Guide
■ In polyphase mode with N
v
vertical taps, N
v
– 1 lines of input are read into line
buffers before any output is ready. As with bilinear mode, there is a scaling ratio
dependent time at the end of a frame where no reads are required as the buffers
are drained.
Enabling run-time control of resolutions affects stalling between frames:
■ With no run-time control, there are about 10 cycles of delay before the behavior
described in the previous list begins, and about 20 cycles of further stalling
between each output line.
■ Enabling run-time control of resolutions adds about 25 cycles of delay between
frames.
Error Recovery
On receiving an early endofpacket signal, the Scaler stalls its input but continues
writing data until it has sent an entire frame. If it does not receive an
endofpacket
signal at the end of a frame, the Scaler discards data until the end-of-packet is found.
On receiving an early
endofpacket signal at the end of an input line, the Scaler II stalls
its input but continues writing data until it has sent on further output line. On
receiving an early
endofpacket signal part way through an input line, the Scaler II
stalls its input for as long as it would take for the open input line to complete,
completing any output line that may accompany that input line. It then continues to
stall the input, and writes one further output line. If it does not receive an
endofpacket signal at the end of a frame, the Scaler II discards data until the
end-of-packet is found.
1 For more information about the stall behavior and error recovery, refer to “Stall
Behavior and Error Recovery” on page 1–3.
Latency
Table 22–1 lists the approximate latency from the video data input to the video data
output for typical usage modes of the Scaler II MegaCore function. You can use this
table to predict the approximate latency between the input and the output of your
video processing pipeline.
The latency is described using one or more of the following measures:
■ the number of progressive frames
■ the number of interlaced fields
■ the number of lines when less than a field of latency
■ a small number of cycles O (cycles)