SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The clock generator subsystem of PCIe PHY module consists of integrated DPLL generator DPLL_PCIE_REF, an APLL high frequency generator for PHY transmision clocks APLL_PCIE and ACSPCIE input/output reference low-jitter clock buffer for connecting with external PCIe device. Figure 26-19 shows the block diagram of Clock Generator Subsistem of PCIe PHY module.
The DPLL_PCIE_REF clock generator receives its input clock directly from PRCM as PCIE_DPLL_CLK (SYS_CLK1 based). The status and control registers for DPLL_PCIE_REF are located in the PRCM module and allow direct programming of the DPLL_PCIE_REF. The output clock of DPLL_PCIE_REF is on output pin CLKOUTLDO and is fed directly in the APLL_PCIE input clock multiplexer. In input mode, the reference low-jitter clock buffer ACSPCIE receives his clock from diferential input pins directly from outside device and after only buffering feeds this clock to the APLL_PCIE input clock multiplexer.
The APLL_PCIE input clock multiplexer chooses the input clock for APLL_PCIE according to register programming and feeds it to the input of APLL_PCIE. The selection of clock source is made by the register PRCM.CM_CLKMODE_APLL_PCIE[7] REFSEL bit as follows:
PRCM.CM_CLKMODE_APLL_PCIE[7] REFSEL = 0b0 - input clock CLKREF_ADPLL, APLL reference input clock is from DPLL_PCIE_REF
PRCM.CM_CLKMODE_APLL_PCIE[7] REFSEL = 0b1 - input clock CLKREF_ACSPCIE, APLL reference input clock is from ACSPCIE
The APLL_PCIE has two output high frequency transmission clocks. The main undivided clock PCIE_PHY_GCLK is delivered from output CLKVCOLDO and is fed directly to the PHY RX module. The second divided clock PCIE_PHY_DIV_GCLK is delivered after passing the main APLL output clock through a by-2-divider (with baypass capabilities) and is outputed on CLKVCOLDO_DIV output. This clock is fed to the PCIe PHY TX modules and delivers sinchronization of the TX modules in two lane mode.