Visible to Intel only — Ixiasoft
Visible to Intel only — Ixiasoft
Data Path | Register Mode | |||
---|---|---|---|---|
Bypass | Simple Register | DDR I/O | ||
Full-Rate | Half-Rate | |||
Input | Data goes from the delay element to the core, bypassing all double data rate I/Os (DDIOs). | The full-rate DDIO operates as a simple register, bypassing half-rate DDIOs. The Fitter chooses whether to pack the register in the I/O or implement the register in the core, depending on the area and timing trade-offs. | The full-rate DDIO operates as a regular DDIO, bypassing the half-rate DDIOs. | The full-rate DDIO operates as a regular DDIO. The half-rate DDIOs convert full-rate data to half-rate data. |
Output | Data goes from the core straight to the delay element, bypassing all DDIOs. | The full-rate DDIO operates as a simple register, bypassing half-rate DDIOs. The Fitter chooses whether to pack the register in the I/O or implement the register in the core, depending on the area and timing trade-offs. | The full-rate DDIO operates as a regular DDIO, bypassing the half-rate DDIOs. | The full-rate DDIO operates as a regular DDIO. The half-rate DDIOs convert full-rate data to half-rate data. |
Bidirectional | The output buffer drives both an output pin and an input buffer. | The full-rate DDIO operates as a simple register. The output buffer drives both an output pin and an input buffer. | The full-rate DDIO operates as a regular DDIO. The output buffer drives both an output pin and an input buffer. The input buffer drives a set of three flip-flops. | The full-rate DDIO operates as a regular DDIO. The half-rate DDIOs convert full-rate data to half-rate. The output buffer drives both an output pin and an input buffer. The input buffer drives a set of three flip-flops. |
If you use asynchronous clear and preset signals, all DDIOs share these same signals.
Half-rate and full-rate DDIOs connect to separate clocks. When you use half-rate and full-rate DDIOs, the full-rate clock must run at twice the half-rate frequency. You can use different phase relationships to meet timing requirements.
Input Path
Each input path contains two stages of DDIOs, which are full-rate and half-rate.
- The pad receives data.
- DDIO IN (1) captures data on the rising and falling edges of ck_fr and sends the data, signals (A) and (B) in the following waveform figure, at single data rate.
- DDIO IN (2) and DDIO IN (3) halve the data rate.
- dout[3:0] presents the data as a half-rate bus.
In this figure, the data goes from full-rate clock at double data rate to half-rate clock at single data rate. The data rate is divided by four and the bus size is increased by the same ratio. The overall throughput through the GPIO IP remains unchanged.
The actual timing relationship between different signals may vary depending on the specific design, delays, and phases that you choose for the full-rate and half-rate clocks.
Output and Output Enable Paths
Each output path contains two stages of DDIOs, which are half-rate and full-rate.
The difference between the output path and output enable (OE) path is that the OE path does not contain full-rate DDIO. To support packed-register implementations in the OE path, a simple register operates as full-rate DDIO. For the same reason, only one half-rate DDIO is present.
The OE path operates in the following three fundamental modes:
- Bypass—the core sends data directly to the delay element, bypassing all DDIOs.
- Packed Register—bypasses half-rate DDIO.
- SDR output at half-rate—half-rate DDIOs convert data from full-rate to half-rate.