Fangyi,
I would like to reference what the Redriver/Retimer flow says about the
time domain flow:
Step 7. The simulation platform performs simulation on the upstream
channel, which consists of Tx1, physical channel 1, and Rx1, according to
the AMI flow defined in the specification for channels without Repeaters.
Step 8a. Redriver: The simulation platform uses the signal waveform at the
output end of Rx1s algorithmic model in step 7, regardless whether Rx1s
AMI_GetWave exists or not, as the stimulus of Tx2s algorithmic model,
regardless whether Tx2s AMI_GetWave exists or not, and performs
simulation on the downstream channel, which consists of Tx2, physical
channel 2 and Rx2, according to the AMI flow defined in the spec for
channels without Redrivers.
Step 8b. Retimer: The simulation platform samples the output waveform of
Retimer Rx AMI_GetWave at ½ UI after each clock tick returned by the
function, generates a digital stimulus as the input to Tx2s algorithmic
model, regardless whether Tx2s AMI_GetWave exists or not, and performs
simulation on the downstream channel, which consists of Tx2, physical
channel 2 and Rx2, according to the AMI flow defined in the spec for
channels without Redriver. The logic level of the digital stimulus is 1 if
sampled value >= Rx1s Rx_Receiver_Sensitivity and 0 if sampled value <=
-Rx1s Rx_Receiver_Sensitivity. If Rx1s Rx_Receiver_Sensitivity <
sampled value < Rx1s Rx_Reciver_Sensitivity, the logic level is unchanged
from the previous bit. The digital stimulus has values of -½ volt for
logic 0 and +½ volt for logic 1.
The flow that Fangyi refers to (highlighted RED) when Tx2 and Rx2 do not
have an AMI_GetWave is on page 178.
Step 6c. If Tx GetWave_Exists is False and Rx GetWave_Exists is False, the
output of Step 4 is convolved with the output of Step 3 by the EDA tool
and the result is passed on to Step 8.
Where
Step 3. The output of Step 2 is presented to the Rx executable model
files AMI_Init function and the Rx AMI_Init function is executed. The Rx
AMI_Init function may modify the impulse response or choose to leave it
unchanged.
Step 4. The EDA tool produces a digital stimulus waveform. A digital
stimulus waveform is 0.5 when the stimulus is "high", -0.5 when the
stimulus is "low", and may have a value between -0.5 and 0.5 such that
transitions occur when the stimulus crosses 0.
Where does this digital stimulus come from. There is only one digital
stimulus in the Redriver Channel, it is the digital stimulus that is the
input to Tx1. When this stimulus is convolved with the IR output of Rx2
then all works perfectly well.
Fangyi has represented the meaning of according to the AMI flow defined
in the spec for channels without Redrivers as using the non-digital
stimulus output of Rx1 as the waveform to convolve with the output of Rx2
AMI_Init, but the spec for channels without Redrivers call for
convolving the output of Rx AMI_Init with a digital stimulus.
The following corrects step 8a in the existing IBIS 6.1 specification to
clarify that there are two cases for time domain simulations. One with
Rx1, Tx1, Tx2 and Rx2 having an AMI_GetWave, and one with Rx1, Tx1, Tx2 or
Rx2 not having an AMI_GetWave. Note that the time domain flow in the
second case will not include any of the AM_GetWave functions that do
exist. Unless Rx1, Tx1, Tx2 and Rx2 are Dual Models any Redriver flow is
problematic. It should be noted that any AMI_Init only model can be
enhanced to include an AMI_GetWave. An alternative solution to this is to
enhance IBIS to include additional IR outputs of AMI_Init that describes
the equalization of the model so that the simulator can implement a proxy
AMI_GetWave function when the AMI_GetWave function does not exist.
Step 8a. Redriver when Tx1, Rx1, Tx2 and Rx2 have AMI_GetWave: The
simulation platform uses the signal waveform at the output end of Rx1s
algorithmic model in step 7 as the stimulus of Tx2s algorithmic model
and performs simulation on the downstream channel, which consists of Tx2,
physical channel 2 and Rx2, according to the AMI flow defined in the spec
for channels without Redrivers.
Step 8b. Redriver when Tx1, Rx1, Tx2 or Rx2 do not have AMI_GetWave: The
output of Step 4 according to the AMI flow defined in the specification
for channels without Repeaters. is convolved with the output of Step 6a by
the EDA tool and the result is passed on to Step 8 according to the AMI
flow defined in the specification for channels without Repeaters.
Step 8c. Retimer: The simulation platform samples the output waveform of
Retimer Rx AMI_GetWave at ½ UI after each clock tick returned by the
function, generates a digital stimulus as the input to Tx2s algorithmic
model, regardless whether Tx2s AMI_GetWave exists or not, and performs
simulation on the downstream channel, which consists of Tx2, physical
channel 2 and Rx2, according to the AMI flow defined in the spec for
channels without Redriver. The logic level of the digital stimulus is 1 if
sampled value >= Rx1s Rx_Receiver_Sensitivity and 0 if sampled value <=
-Rx1s Rx_Receiver_Sensitivity. If Rx1s Rx_Receiver_Sensitivity <
sampled value < Rx1s Rx_Reciver_Sensitivity, the logic level is unchanged
from the previous bit. The digital stimulus has values of -½ volt for
logic 0 and +½ volt for logic 1.
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of RAO,FANGYI
(K-USA,ex1)
Sent: Thursday, May 11, 2017 3:31 AM
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Re: Summary of discussion about BIRD 166.2
All,
One unanimous agreement reached at the May 9 ATM that is missing in
Walters summary is that BIRD166.2 introduces artificial inflation of
redirver nonlinearity (e.g. limiting mode and compression), noise and
crosstalks.
BTW, GetWave-only is a model problem but not a flow problem.
Regards,
Fangyi
From: ibis-macro-bounce@xxxxxxxxxxxxx
<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Wednesday, May 10, 2017 5:16 AM
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx> >
Subject: [ibis-macro] Summary of discussion about BIRD 166.2
All,
Let me summarize the discussion we had on May 9 about BIRD 166.2 by
describing five scenarios, and then some concluding remarks.
Scenario 1, all four AMI models in the Redriver flow (Tx1, Rx1, Tx2, Rx2)
are Init Only models.
The current flow in IBIS 6.1 is flawed because the Rx2 AMI_Init function
does not receive the complete IR input to properly determine its
equalization.
There is unanimous agreement that BIRD 166.2 fixes this for statistical
simulations.
Scenario 2, all four AMI models in the Redriver flow (Tx1, Rx1, Tx2, Rx2)
are Dual models.
The current flow in IBIS 6.1 is flawed because the Rx2 AMI_Init function
does not receive the complete IR input to properly determine its
equalization.
There is unanimous agreement that BIRD 166.2 fixes this for both
statistical and time domain simulations.
Scenario 3, the Tx1 and Rx1 AMI models are Dual Models and the Tx and Rx2)
are Init Only models.
The current flow in IBIS 6.1 is flawed because the Rx2 AMI_Init function
does not receive the complete IR input to properly determine its
equalization.
There is unanimous agreement that BIRD 166.2 fixes the statistical flow,
but the time domain flow remains problematic.
Scenario 4, all four AMI models in the Redriver flow (Tx1, Rx1, Tx2, Rx2)
are a combination of Init Only and Dual models.
The current flow in IBIS 6.1 is flawed because the Rx2 AMI_Init function
does not receive the complete IR input to properly determine its
equalization.
There is unanimous agreement that BIRD 166.2 fixes the statistical flow,
but the time domain flow remains problematic.
Scenario 5, one or more of the four AMI models in the Redriver flow (Tx1,
Rx1, Tx2, Rx2) are GetWave Only models.
There is no valid statistical flow.
The conclusion is that BIRD 166.2 is the correct statistical flow when all
four AMI models in the Redriver flow (Tx1, Rx1, Tx2, Rx2) are a
combination of Init Only and Dual models, and is the correct time domain
flow when all four models are Dual Models.
What I believe IBIS should do is:
1. Approve BIRD 166.2
2. Recommend that all four AMI models in the Redriver flow (Tx1, Rx1,
Tx2, Rx2) are Dual Models in order to support Time Domain flow.
a. Note that any Init Only AMI model can easily be upgraded by the
model maker to a Dual Model.
3. Enhance IBIS AMI by adding additional IR outputs to the AMI_Init
function that contain the linear (CTLE) and non-linear (DFE) equalization
of the model. (Keysight AMI_Init Enhancement)
Which leads to the following questions:
1. Is the Keysight AMI_Init Enhancement necessary if all AMI Models
are Dual Models?
2. Is it easier for a model maker to implement the Keysight AMI_Init
Enhancement instead of making Dual Models?
3. If a model maker is too lazy to make a Dual Model, will he be too
lazy to implement the Keysight AMI_Init Enhancement?
4. Will the EDA tools that are used by model makers implement the
Keysight AMI_Init Enhancement?
Note that the Keysight AMI_Init Enhancement does not address the problem
of AMI_GetWave only models.
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
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