Visible to Intel only — GUID: irb1676546027638
Ixiasoft
Visible to Intel only — GUID: irb1676546027638
Ixiasoft
2.2.1.2. Output Path
Component | Description |
---|---|
Pipeline Registers | Represent pipeline stages in the output path. |
TX FIFO | Stores the data to be transmitted out. |
Shift Register | Delays the enable signal at the read side of the TX FIFO at VCO cycle increment. |
Phase Shift | Delays TX data and strobe at 1/128 of a VCO cycle increments. |
There are two types of delays in the output path, namely inherent latency and output delay, TxDqDelay. The inherent latency is a static delay and is captured in the pipeline stages from the assertion of output enable in the core until the data goes in TX FIFO. The GUI parameter Additional Write Latency is added to the inherent latency.
The TxDqDelay is a dynamic delay and can be reconfigured in the control registers. It is an 11-bit wide register with details described in the following table. It is made up of two parts; the integer part in terms of VCO clock cycles, and the phase shift measured in 1/128 of a VCO clock period. The integer portion of the delay is accomplished using a shift register to delay the enable signal that goes to the read side of the TX FIFO.
Feature | Description | Min | Max |
---|---|---|---|
TxDqDelay [10:7] |
Integer number of VCO clock cycles | 0 | 15 |
TxDqDelay [6:0] |
Additional phase shift measured in 1/128 of VCO clock period | 0 | 127 |
The preceding figure shows an example of TX data transfer in QR DDR. The data_from_core for each pin is 8 bits wide. To enable one extra preamble cycle before the data starts, strobe_out_en should first transition from 0 to 8 one core clock cycle before the data output enable as shown in the figure. Setting Output strobe phase to 90 degrees causes PHY Lite to send the data center aligned.