4. Using GPIO Intel® FPGA IP in Half-Rate Mode
As shown in the Timing Components of a Simplified GPIO Input Path figure, in a half-rate mode interface, the A and B signals go through the HR DDIO IN block and output as DATAOUT[0:3]. Transferring data in half-rate mode reduces the core frequency and therefore augments the setup requirement. However, this solution requires design modifications by changing the GPIO Intel® FPGA IP to half-rate mode. The top_w2 design example shows the full implementation of this solution. The outclk0 clock provides 250 MHz as the full-rate frequency and the outclk1 clock provides 125 MHz as the half-rate frequency.
Figure 7. Block Diagram of Half-Rate Mode Implementation
The following figure shows the timing waveform for the FR DDIO IN register to HR DDIO IN registers in the half-rate mode. The launch clock (outclk0) is operating in full-rate mode while the latch clock (outclk1) is operating in half-rate mode. The DDIO IN data is latched at half-cycle of the launch clock at every 2 ns interval.
Figure 8. Timing Waveform of FR DDIO IN Register to HR DDIO IN Registers
From the HR DDIO IN registers to the FPGA core registers, the data are latched at half-cycle of the launch clock at every 4 ns interval as shown in the following figure.
Figure 9. Timing Waveform of HR DDIO IN Registers to FPGA Core Registers
This design provides a setup slack of 1.617 ns from HR DDIO IN registers to the FPGA core registers. However, this solution utilizes more resources to implement half-rate data transfer in the design.