/sys/class/pps

Field	Value
Subsystem	PPS (Pulse Per Second) core, `drivers/pps/` (`obj-$(CONFIG_PPS) := pps_core.o`, torvalds/linux master)
Config gate	`CONFIG_PPS` (obj line verified against torvalds/linux master 2026)
ABI documentation	`Documentation/ABI/testing/sysfs-pps` (8 What entries; the file carries Date February 2008 but no KernelVersion lines)
Since	not stated: the ABI file has no KernelVersion field (entries dated February 2008)
Live (5.10.134 host)	class directory present, 0 devices (no PPS source registered in the container)
Ledger ID	SYSC-pps

What it represents

One directory per PPS source, ppsX – a signal discipline interface built on hardware pulse-per-second inputs (serial DCD lines, GPIO captures, PTP hardware clock PPS outputs). The ABI calls it “a unified interface to the PPS sources” of the system. The per-source files split in two groups: identity (name, path – empty when the source is not connected to a device, echo – whether the source supports an echo function, mode – functioning mode in hexadecimal, pointing at include/linux/pps.h for the bit definitions) and the event records: assert and clear, each reporting the last timestamp and sequence number of its event kind in the exact format <secs>.<nsec>#<sequence>, empty when no such event has been captured. Consumers pair sysfs discovery with the character device: /dev/ppsN (per Documentation/driver-api/pps.rst) and the PPS_FETCH ioctl from the host header /usr/include/linux/pps.h.

Relationship to the device model

/sys/class/pps/ppsX is a class view over a PPS source device under /sys/devices/... (a tty line discipline, GPIO, or a PTP clock registered as a PPS source – the ptp class’s pps_enable attribute hands PTP hardware PPS events to this subsystem per the sysfs-ptp ABI). No pps bus exists; events flow through the char device, sysfs is introspection. Time-adjacent siblings: rtc, timecard.

Attributes

Attribute	R/W	Unit/format	Conditional?	Source
`ppsX/assert`	RO	last assert event: `<secs>.<nsec>#<sequence>`; empty if none	always (content conditional)	ABI testing `sysfs-pps`
`ppsX/clear`	RO	last clear event: same format; empty if none	always (content conditional)	ABI testing `sysfs-pps`
`ppsX/mode`	RO	functioning mode, hexadecimal; see include/linux/pps.h	always	ABI testing `sysfs-pps`
`ppsX/echo`	RO	whether the source supports an echo function	always	ABI testing `sysfs-pps`
`ppsX/name`	RO	name of the source	always	ABI testing `sysfs-pps`
`ppsX/path`	RO	path name of the connected device; empty if unconnected	always (content conditional)	ABI testing `sysfs-pps`

Safety and writes

The ABI documents all six per-source files as reports – nothing is described as writable, and no capability requirements or error conventions appear in the file. Reading assert/clear is safe and non-destructive; the low-latency capture loop belongs to the char device and PPS_FETCH. Because mode is a hex bitfield defined in include/linux/pps.h, readers need the header to decode it – the ABI deliberately defers the semantics.

References

Documentation/ABI/testing/sysfs-pps (cached copy; online: https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-pps)
Documentation/driver-api/pps.rst (not in sparse cache; /dev/ppsN and ppstest usage cited from it)
/usr/include/linux/pps.h (host header: PPS_FETCH ioctl, mode bits)
drivers/pps/Makefile (torvalds/linux master; fetched obj line)
Ledger row SYSC-pps; /sys/class/pps present with 0 devices per source-cache/live-sys/class-list.txt
Sibling pages: ptp, rtc, timecard