Altera SDC and TimeQuest API - Manual (Page 152)

2–142 Chapter 2: SDC and TimeQuest API Package and Commands
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SDC and TimeQuest API Reference Manual © December 2009 Altera Corporation
report_rskm
Usage
report_rskm [-append] [-file <name>] [-panel_name <name>] [-stdout]
Options
-append: If output is sent to a file, this option appends the result to that file.
Otherwise, the file will be overwritten
-file <name>: Sends the results to an ASCII or HTML file. Depending on the extension
-panel_name <name>: Sends the results to the panel and specifies the name of the new
panel
-stdout: Send output to stdout, via messages. You only need to use this option if you
have selected another output format, such as a file, and would also like to receive
messages.
Description
Reports RSKM for dedicated LVDS circuitry.
In designs that use dedicated LVDS circuitry, receiver input skew margin (RSKM) is the time margin
available before the LVDS receiver megafunction fails to operate. RSKM is defined as the total time margin
that remains after subtracting the sampling window (SW) size and the receiver channel-to-channel skew
(RCCS) from the time unit interval (TUI), as expressed in the following formula:
RSKM = (TUI - SW - RCCS) /2
The time unit interval is the LVDS clock period (1/fmax). The sampling window is the period of time that
the input data must be stable to ensure that the data is successfully sampled by the LVDS receiver
megafunction. The sampling window size varies by device speed grade. RCCS is the difference between
the fastest and slowest data output transitions, including the tco variation and clock skew. To obtain an
accurate analysis of an LVDS circuit, you should assign an appropriate input delay to the LVDS receiver
megafunction. RCCS is equal to the difference between maximum input delay and minimum input delay.
If no input delay is set, RCCS defaults to zero.
Example
project_open top
create_timing_netlist
read_sdc
update_timing_netlist
# Ensure a tccs of 1ns
set_input_delay -max -clock lvds_clk 2ns [get_ports lvds_input]
set_input_delay -min -clock lvds_clk 1ns [get_ports lvds_input]
# Show lvds information
report_rskm