diff --git a/doc/other.xml b/doc/other.xml
index 3654f28..3a5479f 100644
--- a/doc/other.xml
+++ b/doc/other.xml
@@ -2010,6 +2010,117 @@ should get latched?
+
+
+National instruments General Purpose Counters/Timers (GPCT)
+
+
+Counters/timers and pulse generators are fairly different in terms of
+functionality, but they correspond to similar devices seen either as input
+or output. When generalising, these devices are both referred to as
+"counters". The NI boards provide a couple of such counters, under the name of
+GPCT.
+A counter is made of the following basic elements:
+
+
+ Input source
+ the signal measured or the clock of the pulse generation.
+
+
+ Gate
+ controls when the counting (or sampling) occurs.
+
+
+ Register
+ holds the current count.
+
+
+ Out
+ for the output counters (pulse generators), the output signal.
+
+
+
+
+There are many different ways to count, time or generate pulses. All the modes
+rely on the counter and some particular configuration. For example, in a typical
+buffered counting mode, the source is the (digital) signal that is measured, the
+counter is increased at every rising edge of the signal, the gate is the
+(digital) signal indicating when to save the counter to memory. It is preferable
+you get first familiarized with these various modes by reading your NI board
+documentation before reading the following description on the mapping to the
+comedi interface.
+
+
+
+Each counter of the board is represented in comedi as a subdevice of type
+COMEDI_SUBD_COUNTER. Each subdevice has a device file
+associated (eg, /dev/comedi0_subd11) in order to read or
+write buffered data from or to the counter.
+Note that the comedi subdevice has three "channels". In most case, only channel
+0 is to be used. Reading or writing on channel 0 corresponds to reading/writing
+the counter value. The GPCT also has two registers named A and B, they can be
+accessed respectively via channels 1 and 2.
+
+
+
+To configure the behaviour of the counter with comedi, the
+function comedi_set_counter_mode is used.
+The possible mode values are to be found in the ni_gpct_mode_bits
+enum constants. For instance, by default the counter is cumulative, even in
+buffered counting. To reinitialise it after each sampling (ie, after an edge on
+the gate signal), one can add the NI_GPCT_LOADING_ON_GATE_BIT
+to the mode. In that case, the counter will be reset to the value of the A
+register after each sampling.
+
+
+
+To configure the signal to be used as the "source", one uses the
+comedi_set_clock_source with one constant from the
+ni_gpct_clock_source_bits enum. When the period of the signal is
+fixed and known, it should be specified as the last parameter of the method, otherwise
+0 should be passed. Note that in comedi this is called "clock"
+because in timer and pulse generator, this signal is used as the clock.
+
+
+
+To configure the signal to be used as the "gate", one uses the
+comedi_set_gate_source with one constant from the
+ni_gpct_gate_select enum. When the gate signal is not be used,
+NI_GPCT_DISABLED_GATE_SELECT should be specified. Some
+NI boards have two gates, but the behaviour associated with the second gate is
+usually unknown so it is recommended to disable it. Note that this is called
+"gate" because in some modes, this signal is used to block/unblock the counter.
+
+
+
+The function comedi_reset will stop and reset a counter.
+After being configured, to start a counter, it should be "armed", which can be
+done either with the comedi_arm function (for simple counting
+mode), or with the start_src member of the command
+(for buffered counting).
+
+
+
+One side thing to mention is the signal routing of the NI card, which is done
+via the PFIs (Programmable Function Inputs).
+NI's naming is confusing because they use the same name for the
+terminal (ie, physical input/output pins) and for the signal
+(ie, the logical information that controls/indicates a specific event).
+
+The routing allows to configure which signal goes to a PFI terminal.
+This is done via comedi_set_routing, with subdevice being
+the special DIO comedi subdevice (eg, 7 on M-series), the PFI terminal
+number as channel, the signal that should be routed to it encoded as source with
+one of the constants from the ni_pfi_routing enum.
+The direction of the pin must also be correctly configured (ie, whether it is
+used as input or output). This is done via comedi_dio_config
+with the same subdevice and channel, and either COMEDI_INPUT
+or COMEDI_OUTPUT.
+
+
+
+
+
National instruments RTSI trigger bus