SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
Figure 28-22 is a simplified block diagram of the APLL_PCIE instance integrated in the PCIe PHY clock generator subsystem.
The input clock CLKINP goes to a predivider with fixed value. Then goes to the clock generation loop with fixed Feedback Divider. The output of the VCO is split in two. One path directly goes out on CLKVCOLDO output. The other path passes the internal divider by 2 and then goes to bypass multiplexor where is selected the output frequency of the CLKVCOLDO_DIV output. The selection is made either from "Rate" signal from PCIe_SS controller or with higher priority from Force bypass signal controlled from PRCM.CM_CLKMODE_APLL_PCIE[8] CLKDIV_BYPASS bit.
The frequency of the VCO output is fixed to 2.5 GHz and is not programmable in software. No changes could be made on the internal parameters of the APLL_PCIE. Output clocks are controllable through PRCM registers and can be gated by software. See Section 28.4.4.4.2.4.2.1 PCIe PHY APLL Output Clock Gating for more information.