[SI-LIST] Re: setup & hold Time for source synchronous
- From: "S. Weir" <weirsp@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 07 Aug 2001 11:26:44 -0700
Bill, the evil skew, being an uncertainty, takes away from both setup and hold.
Regards,
Steve.
At 06:00 PM 8/6/01 -0700, Bill Chen wrote:
> I don't agree with Richy's Equations.
>In the equation given, Tflight_skew_max is subtracted
>in both setup and hold equations and this is incorrect.
>If the Tfligh_skew reduces your setup margin, it may
>increase your hold time margin. On the other hand, if it
>improves you setup margin, it will reduce your hold time
>margin. That's the reason that design engineers sometimes
>on purposely skew the data / clock signals to balance
>setup / hold time margins.
>
> Here is my version of setup/hold equations for your
>reference:
>
>Tsetup_margin = T_available_setup_time_at_driver -
> T_interconnect_flight_skew_clk_leading_data_max -
> Tsetup_at_receiver
>
>Thold_margin = T_available_hold_time_at_driver -
> T_interconnect_flight_skew_clk_trailing_data_max -
> Thold_at_receiver
>
> Where: T_available_setup_time_at_driver and
> T_available_hold_time_at_driver
> are Time data_valid_before_clock_min and
> Time data_valid_after_clock_min
>
> and
> T_interconnect_flight_skew_clk_leading_data_max,
> T_interconnect_flight_skew_clk_trailing_data_max
> are skew between data and clock signals with reference
> to clock signal. please note that these two terms may
> be positive or negative. So the skew may increase or
> decrease setup or hold time margin.
>
> For example, if clock is actually skew more than data
> signals, the T_interconnect_flight_skew_clk_leading_data_max
> becomes a negative number, the maximum time clock leading
> data should use the minimum absolute skew between clock and
> data {Think about Max(-1ns, -1.2ns, -1.5ns) = -1ns}.
> And in this situation, the setup margin is improved
> comparing with 0 skew between clk/data. Same principal
> holds true for the other term.
>
>
>
> Let me know if you have any comments!
>
>Thanks!
>
>======================================================
>Bill (Qinghua) Chen, Ph.D.
>
>Technical Leader
>Andiamo Systems Inc.
>375 E. Tasman Dr. Bldg 6 Phone: (408)527-4982
>San Jose, CA 95134 Email: billchen@xxxxxxxxxxx
>======================================================
>
>
>
>
>
> Let me know if you have any questions.
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Issa, Elie
>Sent: Friday, August 03, 2001 2:49 PM
>To: Lai, Ricky (Eng Hou); 'si-list@xxxxxxxxxxxxx'
>Subject: [SI-LIST] Re: setup & hold Time for source synchronous
>
>
>
>Thanks!
>
>-----Original Message-----
>From: Lai, Ricky (Eng Hou)
>Sent: Friday, August 03, 2001 1:44 PM
>To: Issa, Elie; 'si-list@xxxxxxxxxxxxx'
>Subject: [SI-LIST] Re: setup & hold Time for source synchronous
>
>
>
>The correct equation should be:
>Setup margin = Budget - (T_data_valid_before_stb_min) - (Tflight_skew_max) -
>Tsetup
>Hold margin = Budget - (T_data_valid_after_stb_min) - (Tflight_skew_max) -
>Thold
>
>-----Original Message-----
>From: Issa, Elie
>Sent: Friday, August 03, 2001 11:26 AM
>To: 'si-list@xxxxxxxxxxxxx'
>Subject: [SI-LIST] setup & hold Time for source synchronous
>
>
>
>Dear SI Gurus:
>I need your help in verifying some derivation for setup & hold equations
>for GTL bus
>for source synchronous clocks.
>
>The equation for setup is:
>Tco(strobe)min + Tflight(strobe)min - Tco(data)max -Tflight(data)max
>-Tsetup= Tmargin_setup
>
>The equation for hold time was:
>Tco(data)min + Tflight(data)min -Tco(strobe)max -Tflight(strobe)max
>-Thold= Tmargin_hold
>
>The skew for the strobe & data flight time should be very small. Whenever,
>I fit the variable given in the
>specs into the equation, the margin comes negative.
>
>I would think that there must be a ValidBefore and ValidAfter variable to be
>included in the equation.
>Yet the specs claim the ValidBefore is only [Tco(strobe)min-- Tco(data)max].
>
>
>Any input would be greatly appreciated!
>
>Regards
>Elie
>
>
>
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