[ahmadexp]

Summary

• read the SA5x PpsWidth setting during oscillator initialization
• set it to the required 80 ms value when it is missing or incorrect
• add pseudo-terminal regression coverage for both update and no-op paths

Motivation

The repository already lists {set,PpsWidth,80000000} as a minimum required SA53 setting, but oscillatord did not enforce it. On hardware, a missing width caused the Time Card PHC to remain unsynced after boot with a stable offset of hundreds of milliseconds, while GNSS and MAC PPS remained closely aligned.

The setting is applied at daemon startup. It is not stored to EEPROM, avoiding unnecessary flash writes while ensuring every oscillatord run establishes the required output geometry.

Testing

Ran the same Ubuntu 24.04 build used by .github/workflows/oscillatord.yml:

BUILD_TYPE=RelWithDebInfo BUILD_TESTS=ON BUILD_UTILS=ON bash ./tools/build-timecard.sh

100% tests passed, 0 tests failed out of 2

The new test uses a pseudo-terminal SA5x responder and verifies that oscillatord sends {set,PpsWidth,80000000} only when the reported value differs.