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This directory contains the device entries for the quad event and
frequency counter.


HARDWARE
The quad event/frequency counter provide four independent event
or frequency counters.  The first counter input in on the lowest
numbered pin on the connector (pin 2 or pin 10).  The fourth
counter is on the highest numbered pin on the connector (pin 8
or pin 16).  The maximum counter input frequency is 1.25 MHz.


DEVICE NODES
The device interfaces to the quad event/frequency counters offer
a select()'able interface to the latest readings, a configurable
update rate, and an accumulated total that can be initialized.

.../update_period0, update_period1, update_period2, update_period3
   This specifies the update period for count0 in milliseconds.
That is, a select() on count0 will will make a file descriptor
readable every update_period0 milliseconds.  Setting this to
zero turns off timed updates and causes an update whenever there
is activity on the counter input.  A value of zero is often
used to detect infrequent bursts of count pulses on the input.
The value chosen for update_period must be a multiple of four
milliseconds.  This is a read-write node.

.../count0, count1, count2, count3
   The accumulated counts in the last update_period0 milliseconds.
The value is printed as an numeric string terminated by a newline.
Use an int or long long data type to read this depending on your
update_period0 value.  Output from count0 can be used with a
select() statement.  The count value sample period is crystal
controlled making the count0 value usable as a frequency estimate.
The frequency is (count0 * (1/update_period0)) KHz.  This is a
read-only node.

.../total0, total1, total2, total3
   The running sum of all count0 readings.  This is a long long
(i.e. 64 bit) number printed as an ASCII string terminated by a
newline.  This is a read-write node.  You can initialize it with
a write.