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Ixiasoft
1.2.5.1.1.4. Core PLL
The core PLL uses an external clock input as its reference clock to generate two derivative clocks from a single VCO:
- Link clock
- Frame clock
Clock | Formula | Description |
---|---|---|
Link Clock | Serial data rate/40 | The link clock clocks the JESD204B IP core link layer and the link interface of the transport layer. |
Frame Clock | Derived based on settings; refer to Table 13. | The frame clock clocks the transport layer, test pattern generators and checkers, and any downstream modules in the FPGA core fabric. |
For the frame clock, when the F parameter is 1, 2 or 3, the resulting frame clock frequency easily exceeds the capability of the core PLL to generate and close timing. The top level RTL file, (altera_jesd204_ed_<data path>.sv), defines the frame clock division factor parameters, F1_FRAMECLK_DIV (for cases with F = 1) and F2_FRAMECLK_DIV (for cases with F = 2). This factor enables the transport layer and test pattern generator to operate at a divided factor of the required frame clock rate by widening the data width accordingly.
As an example, the actual frame clock for a serial data rate of 10 Gbps and F = 1 is:
(10000/(10 × 1)) / F1_FRAMECLK_DIV = 1000 / 4 = 250 MHz
Frame Clock and Link Clock Relationship
The frame clock and link clock are synchronous. For the derived F mode, the ratio of link_clk period to frame_clk period is given by this formula:
link_clk period to frame_clk period ratio = 32xL/(MxSxN')
F Parameter | fTXframe(txframe_clk frequency) | fRXframe(rxframe_clk frequency) |
---|---|---|
1 | fTXlinkx(4/F1_FRAMECLK_DIV) | fRXlinkx(4/F1_FRAMECLK_DIV) |
2 | fTXlinkx(2/F2_FRAMECLK_DIV) | fRXlinkx(2/F2_FRAMECLK_DIV) |
4 | fTXlink | fRXlink |
8 | fTXlink/2 | fRXlink/2 |