Module timestamp 

The counter a concentrator stamps packets against.

Every packet the chip hears carries the value of a counter running at 32 MHz, and every packet the chip sends at a chosen moment is given a value of that same counter. It is what a receive window is measured against, so a gateway that answers an uplink is really doing arithmetic on this counter and nothing else.

Two things make it harder than reading a number. The counter is 27 bits wide, so it rolls over about every two minutes, and the chip does not say how many times it has. A reader therefore keeps a little state: the last value it saw and how many times it has seen the count go backward. A packet is widened against that same state, and the rule is not the same one, because a packet whose count is above the last reading was heard before the most recent rollover rather than after it.

Nothing here reads a register. The bytes come from one burst and this turns them into a counter, so the arithmetic can be checked without hardware.

Structs

Counter

Both counters a concentrator keeps.

Tracked

One counter, and what is known about how often it has rolled over.

Constants

COUNTERS

Where both counters are read from, in one burst.

COUNTERS_LEN

How many bytes that burst carries: four for each counter.

COUNTER_BITS

How many bits the counter actually holds.

TICKS_PER_US

How many ticks of the counter make a microsecond.

WRAPS

How many rollovers are counted before the count itself repeats.

Functions

disagrees

Whether a second reading of the counters disagrees with the first.