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Ixiasoft
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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 the TX FIFO. The parameter option Additional Write Latency is added to the inherent latency.
You can configure the 11-bit dynamic delay register, TxDqDelay, in the control registers. The TxDqDelay register consists of two parts, as listed the following table. The integer part of the delay uses 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. 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. | 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, wait for strobe_out_en to transition from 0 to h8 in one core clock cycle before the oe_from_core signal, as shown in the figure. Setting Output strobe phase to 90 degrees causes PHY Lite to send the data center aligned.