Visible to Intel only — GUID: epx1689204954561
Ixiasoft
Visible to Intel only — GUID: epx1689204954561
Ixiasoft
2.2.1.3. Input Path
The simplified input path of the IP consists of the pipeline registers, receiver FIFO, shift registers, and phase shift logics.
Component | Description |
---|---|
Pipeline Registers | Represent pipeline stages in the input path |
2x RX FIFOs | Perform 2:1 rate conversion on the RX data
|
Shift Registers | Perform the following functions:
|
Phase Shift Logics | Perform the following functions:
|
Delay | Type | Description |
---|---|---|
Inherent latency | Static | Captured in pipeline stages from the assertion of group_<n>_rdata_en signal in core until internal signal, RcvEn, is asserted. |
RcvEn delay (internal signal generated from input signal rdata_en) | Dynamic | You can reconfigure these delays in the control registers. You can program the RcvEn delay statically or dynamically through the Additional Receiver Enable Latency settings in the IP Parameter Editor. |
Positive-edge strobe_in delay | ||
Negative-edge strobe_in delay | ||
rdata_valid delay |
Feature | Description | Bit-field Description | Min | Max |
---|---|---|---|---|
RxRcvEnPiRank0[10:7] |
|
Bit 10 to bit 7 represents integer number of VCO clock cycles to delay RcvEn signal. | 0 | 15 |
RxRcvEnPiRank0[6:0] | Bit 6 to bit 0 represents additional phase shift in RcvEn signal measured in 1/128 of VCO clock period. | 0 | 127 | |
RxDqsNDelayPi[6:0] |
|
Phase shift in the negative edge of the DQS for each pin measured in 1/128 of VCO clock period. | 0 | 127 |
RxDqsPDelayPi[6:0] | Phase shift in the positive edge of the DQS for each pin measured in 1/128 of VCO clock period. | 0 | 127 | |
read_enable_offset[3:0] |
|
Delay before reading from the RX FIFO measured in number of PHY clock cycles. | 0 | 15 |
The preceding figure shows an example of RX data transfer in QR DDR. In this illustration, the data_to_core output signal to the FPGA fabric for each pin is 8 bits wide. The PHY Lite IP uses DDR4 preamble settings, expecting one cycle of preamble by default.
Setting the parameter Capture strobe phaseshift to 90 degrees in the IP Parameter Editor, as shown in the following figure, causes the PHY Lite IP to accept edge-aligned input data, data_in, with respect to the input strobe signal, strobe_in.
The inherent latency in the RcvEn path measured from the assertion of read enable in the core until the RcvEn signal (internal) is asserted is presented in the following table. The parameter Additional receiver enable latency is added to the inherent latency. The maximum allowed value for this parameter is shown in the third column in the following table.
I/O Frequency (MHz) | Inherent Latency in the RcvEn Path (# of IO Clock Cycles) | Maximum Additional RcvEn Latency |
---|---|---|
600 - 1250 | 27 | 15 |
300 - 600 | 13 | 7 |
150 - 300 | 7 | 3 |
To ensure that the IP uses only clock edges associated with valid input data, gate the receiver off when PHY Lite for Parallel Interfaces IP is not accepting input data. If there are extra toggling signals or noise on the DQS port, use a refined version of the received strobe. The gating signal, RcvEn (receiver enable), is derived internally from the rdata_en signal. Use the RcvEn signal to ungate the DQS gate window by asserting RcvEn up to one cycle before the first rising edge of DQS, as shown in the following figure. You require no more than one cycle preamble in the strobe signal.
The process of shutting off the DQS gate happens automatically after the last burst ends.
In the input path, program the on die termination (ODT) and sense amplifier (SA) when you dynamically reconfigure the RcvEn delay.
To save power in idle mode, gate off the ODT and SA using two enable signals tapped from the same shift register as RcvEn.
- DqsSenseAmpDelay
- DqsSenseAmpDuration
- DqSenseAmpDuration
- DqSenseAmpDelay
- DqOdtDuration
- DqOdtDelay
- DqsOdtDuration
- DqsOdtDelay
RxRcvEnPi[10:7]>>Gear42 | DqsOdtDelay | DqOdtDelays | Dq/Dqs SenseAmpDelay |
---|---|---|---|
0 | 2 | 3 | 3 |
1 | 3 | 4 | 4 |
2 | 4 | 5 | 5 |
3 | 5 | 6 | 6 |
4 | 6 | 7 | 7 |
5 | 7 | 8 | 8 |
6 | 8 | 9 | 9 |
7 | 9 | 10 | 10 |
When changing the RcvEn coarse delay or RxRcvEnPiRank0[10:7], Intel recommends that you update read_enable_offset to avoid receiving misaligned data in the core. The small values of read_enable_offset can cause RX FIFO underflow, while large values may cause an overflow.
RxRcvEnPiRank0[10:7] | Allowed values for read_enable_offset |
---|---|
0, 1, 4, 5, 8, 9, 12, 13 | 3, 5, 7, 9, 11 |
2, 3, 6, 7, 10, 11, 14, 15 | 4, 6, 8, 10, 12 |