PT_CounterFreqStart 

typedef struct tagPT_CounterFreqStart
{
    INT16U counter;
    INT16U GatePeriod;
    INT16U GateMode;
} PT_CounterFreqStart, * LPT_CounterFreqStart;

PT_CounterFreqStart is used in function DRV_CounterFreqStart. 

Member Description

Name Direction Description
counter input The channel number of the specified counter.
From a minimum of zero for the first channel to the maximum channel number minus one. For example, the range is from 0 to (N-1) on a device with N counter channels.
For AMD9513 chip, the frequency measurement needs the simultaneous operation of two counters (refer to hardware manuals), it should follow specific rules when selecting the channel. For example, as for PCI1780, two adjacent channels operate simultaneously during the frequency measurement, so the target channels can be 0, 2, 4 and 6.
GatePeriod input The gating period in seconds estimated by user.
This parameter in only used for AMD Am9513A.
User can set it a value between 0 and 2000ms by estimation.
When 0 is set, the driver will select a proper value automatically.
GateMode input Reserved.

Note:

For Intel 8254 chip, there is no "gate period" counter. The driver uses the windows system timer to calculate the time period between two samples. The frequency is then derived from the time period and count increment. So user should set a proper sample frequency accordingly to avoid counter overflow which may cause inaccurate frequency measurement.