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#chrony
2 posts
Precision timing
8 min
The clock that rang like a bell under load
I built a PRU clock that held nanoseconds on the bench, then rang under load. The daemon crossing its ticks into CLOCK_REALTIME was modeling chrony's own steering and feeding the model back. I fixed it by moving the reference out of userspace, into a Linux PTP hardware clock.
#gps#pps#ptp#beaglebone
Precision timing
4 min
The GPS that answers 0xFF when it has nothing to say
Reading a u-blox GPS over I2C frees the UART, but the I2C interface has no concept of idle. When the module has nothing to send, every read comes back as 0xFF filler. This is the small bridge that turns that into a chrony refclock.
#gps#i2c#chrony#timing