Timing constraints for ALTLVDS I/O

Actually, there's no need to constrain the LVDS blocks in Altera devices. This is a hard IP block that has been characterized and guaranteed to work. The timing information is contained in a marco model... This simply means the individual delays within the LVDS block is lumped into a few large delays. Unlike the individual logic and interconnect delays you would get in the FPGA core.

TimeQuest does provide two timing reports that allow you to report LVDS specific info: report_rskm and report_tccs.

Input into the LVDS block - report_rskm

This command works when a hard LVDS has been instatinated in the design.

In designs that use the LVDS I/O standard, 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 transmitter channel-to-channel skew (TCCS) from the time unit interval (TUI), as expressed in the following formula:

RSKM = (TUI - SW - TCCS) /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. TCCS is the difference between the fastest and slowest data output transitions, including the tCO variation and clock skew. In order to obtain an accurate analysis of an LVDS circuit, you should assign an appropriate Input Delay to the LVDS receiver megafunction. TCCS will be equal to the difference between max input delay and min input delay. If no input delay is set, TCCS will default to zero. So, to set the TCCS parameter, above, use the set_input_delay -max and set_input_delay -min => TCCS = delay_max - delay_min.

Output of the LVDS block - report_tccs

In designs that use the LVDS I/O standard, transmitter channel-to-channel skew (TCCS) is the timing difference between the fastest and slowest output transitions, including tCO variations and clock skew.

Also, this is a pretty cool feature in Quartus.... go to the command prompt and type: quartus_sh --qhelp. You'll get a nice dialog box listing all Command Line and API info. Take a look at the sta and sdc packages! =)