Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 7/19/2024
Public

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5.1.6.11.1. SMTG Hub Overview

The SMTG hub supports a synchronized multi-domain time stamp (TS) capture, concurrently triggered from multiple sources. The HPS system timer and the ToD counter implemented in FPGA fabric are used to obtain a synchronized TS. The cross-time stamp time-synchronization provides a mechanism to determine the time and frequency offset among the different domains. It allows the software to trigger a time sampling event, where the event is routed to each supported time domain to capture the respective domains time at the same point. Within a time domain, the time stamp provides information about the domain time at the point of sampling. Time stamps for multiple time domains provide the time correlation among these domains, where with simple calculation, the relative frequency among the domains can be determined and subsequently the time deltas of these domains can be known.

With time stamps of the local time and the remote time that correspond to each other, software can then determine the relationship between them and use it for scheduling events to take effect at a specific point in time, or for disciplining the clocks of the local time base that need to be adjusted due to frequency drift.

The figure below demonstrates one or more TS sources reaching the SMTG hub with 64-bit TS values, with the source from the HPS system timer or FPGA fabric ToD counter.

The hub interfaces with XGMAC core which is the host and provides access to the memory-mapped registers which contain captured TS values and other configuration and status data. The host is using a general purpose output to generate a level signal to initiate a sync pulse on the sync wire that is connected to the Aux TS Snapshot input of XGMAC for synchronized TS capture of XGMAC’s internal ToD value. Internally, the same sync pulse is used to trigger capture of TS from other sources, in this case, the HPS system timer or ToD counter in the FPGA fabric.
Figure 82. Synchronized Multidrop Timestamp Gathering (SMTG) Architecture