Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 11/27/2024
Public
Document Table of Contents

7.5.1. Hardware-Managed Clocks

The following is a list of features in HW-managed clocks:

  • To maintain fixed frequencies, an external ping-pong counter divider is used for the main divider. SW can write a new counter value in boot mode, and the new value is applied when boot mode is exited.
  • PLL internal dividers are set to a fixed value to divide down the required VCO to the correct base frequency. For example, the MPU clock requires the VCO to run at 4/3.6/3.2/3 GHz to meet the jitter requirement for a 2/1.8/1.6/1.5 GHz MPU clock. In this case, the internal divider is fixed at 2.
  • HW-managed clocks transition in the following categories:
    • Entering boot mode via a reset manager request (HW)
    • Entering boot mode via a clock manager CSR write (SW)
      • SW may change HW-managed counters/dividers in boot mode
    • SW exits boot mode via a clock manager CSR write
      • If SW changed the HW-managed counters/dividers, the clocks obtain the new values after exiting boot mode
      • Must also clear the external counter reset bits
    • SW switching external bypass of MPU, APS, or PSS group
  • HW-managed clocks are only transitioned through HW control
  • To implement these features, HW-managed clocks are coupled to the clock manager sequencer in l4_sys_free_clk which communicates through standard asynchronous design blocks to each HW-managed PLL clock domain

There are two groups of HW-managed clocks:

  • MPU: Consists of the clocks internal to the MPU ARM complex and APS.
  • PSS: Consists of the 7 synchronous NOC clocks. System level debug clocks are included in this group because they are synchronous to the NOC.