[SI-LIST] Re: DDR timing equation question

Jean-Pierre,

TOF DQS and DQ is the flight time on interconnect for DQS and DQ
signals. Tdelay is the internal delay (on-die) that is intentionally
added to dqs only. Remember, during DDR writes DQ and DQS are launched
with a 90 degree phase delay such that DQS edge is centered in the DQ
bit. This allows DRAM to latch the data with sufficient steup/hold.
However, on read cycles DQ anf DQS are launched simultaneously.
Therefore memory controller has to internally delay DQS in order to
latch the data. TDSFF and TDHff are the setup and hold requirements for
flip-flop that latches in the data.

Regarding your second question about ISI. Typically you shouldn't have
to. If you are using a decent PRBS pattern then the ISI effects are
already included in your simulation results. Note that for setup/hold
you are taking max DQ, min DQS or vice versa. These min/max flight times
already include ISI effects.

Thanks,

Yasir Mirza


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of BOUTHEMY JEAN PIERRE
Sent: Tuesday, March 27, 2007 9:25 AM
To: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Cc: BOUTHEMY JEAN PIERRE
Subject: [SI-LIST] DDR timing equation question

Hello SI experts,=20
I have to solve for a DDR interface issue when traffic is full bandwith
(1Gb/s): DDR is then blocked and we can not access to it anymore.=20
Note that this "should not be" a card bug because it happens only on a
few cards.=20
FYI, the Controller is an Intel Network Processor IXP2400.=20
I would like to check the timing but I have to know the setup and hold
time equations.=20

I found on an Intel Powerpoint the following equations, for READ access
(data from DDR to NPU):=20

        * Tsetup =3D Tdelay - Tdqsq max + TOFdqs min - TOFdq max

        * Thold =3D Tqh - Tdelay + TOFdq min - TOFdq max

The file can be viewed from the following URL:=20
www.ee.sc.edu/classes/Spring07/elct865/Class_Notes/ClassNotes1_Summary86
5.ppt

When we observe the waveform on slide 111, I don't understand what is
the difference between Tdelay and TOF dqs?=20
Can someone explain in details how should be interpreted Tdelay and the
DDR hold time calculation in general ?=20

Note that I would like to minus the ISI value on DQ data on these
equations: am I right? =20

Thank you,=20
Regards,=20

Jean-Pierre.=20



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