Visible to Intel only — GUID: iga1401395567274
Ixiasoft
Visible to Intel only — GUID: iga1401395567274
Ixiasoft
3.2.3. Fill Level
The dual-clock FIFO core has two fill levels, one in each clock domain. Due to the latency of the clock crossing logic, the fill levels reported in the input and output clock domains may be different at any given instance. In both cases, the fill level is pessimistic for the clock domain; the fill level is reported high in the input clock domain and low in the output clock domain.
The dual-clock FIFO has an output pipeline stage to improve fMAX. This output stage is accounted for when calculating the output fill level, but not when calculating the input fill level. Hence, the best measure of the amount of data in the FIFO is given by the fill level in the output clock domain, while the fill level in the input clock domain represents the amount of space available in the FIFO (Available space = FIFO depth – input fill level).