The PMC has three source clocks:
- REF_CLK device pin input
- PMC_IRO_CLK, an internal ring oscillator (IRO) (aka SysOsc)
- Real-time clock (RTC) driven by an external crystal
REF_CLK Device Pin input
The REF_CLK is typically driven by a 33 MHz external LVCMOS clock signal and is used to drive the five PLL clock generators in the PMC, LPD, FPD, and CPM.
PMC_IRO_CLK Oscillator
The PMC_IRO_CLK is internal to the device and is generated by a self-starting internal ring oscillator (IRO). This clock is used within the PMC for the RCU and PPU processors, their AXI interconnect, and the security module. The IRO frequency is trimmed to the specification defined in the Versal ACAP data sheets listed in References.
Crystal-driven RTC
The RTC is driven by an external 32.768 kHz crystal. The clock is consumed within the RTC time keeper. The RTC provides a calibrated time reference based on the attached clock crystal. The clock can be calibrated for greater accuracy. When the device is powered down, the RTC is operated by the battery. The RTC is described in Real-Time Clock.
Summary of Primary Clock Sources and Their Destinations
The primary clock sources are listed in the table.
| Clock Name | Usages |
|---|---|
| REF_CLK device pin | PLL clock generators in PMC, LPD, FPD, and CPM |
| PMC_IRO_CLK oscillator | PMC-only: processors, interconnect, and security module |
| RTC_CLK crystal | RTC and battery-backed RAM within the PMC |