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SciSDK Library
SDK for SciCompiler projects
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SciSDK Library
SDK for SciCompiler projects
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The time of flight spectrum is an histogram used to measure the time delay between a T0 and a trigger events. The T0 is a reference event that is used to synchronize the acquisition of the data. The trigger event is the event that is used to measure the time delay. For example the T0 can be a laser digital trigger pulse and the trigger event can be a photon detected by a PMT. The laser pulse can irragiate a biological sample and the PMT observe the photons generated by the flourescence of the sample. The time of flight spectrum is used to measure the time delay between the laser trigger and the photons arriving on the detector displaying as an histogram. In another application ToF spectrum can be used for neutron ToF Spectroscopy. In this case the T0 is for example the synchrotron kicker signal or the chopper sync pulse and the trigger event is a neutron detected by a neutron detector (ie He3 tube).
The ToF component in SciCompiler has indeed two input:
There is a minimum delay between the T0 and the first event, this can be configured with parameter start_delay. Any events before this delay are discarded. The histrogram start after the start delay In any case, at least one clock cycle between T0 and first event must be present.
dead time: the bin width, expressed in clock cycles, is configured with parameter binwidth. A bin width of 3 clock cycles must be respected to allow the internal FPGA logic to switch between each bin.
So the time base (x bin on the histogram) is given by the formula: binwidth * clock_period * index_of_the_bin
Every time a T0 is received, the ToF resets the index_of_the_bin and accumulate counts in the specific bin of the histogram. For example, if the binwidth is set to 10 and the clock of the board is 100 MHz, each bin will last 100ns. The T0 rising edge force the bin of the ToF to go back to 0 but it will not reset the histogram. The histogram will accumulate counts in the bin 0 from T0 to 100ns than it will pass to bin 1 from 100ns to 200ns and so on.
When a second T0 is received, the index_of_the_bin if forced back to 0 and the histogram is restart to integrate on bin 0. The histogram will accumulate counts in the bin 0 from T0 to 100ns than it will pass to bin 1 from 100ns to 200ns and so on.
If the histogram has (for example) 1024 bins two thinks can happen:
An TOF spectrum has the following parameters taken from the JSON file:
Number of bins and number of bits define the memory occupancy of the spectrum indeed they are defined at compile time by SciCompiler.
The following parameters can be configured:
| Parameter | Acces Mode | Description | Default value |
|---|---|---|---|
| binwidth | R/W | set x-axis bin size in clock cycles, minimum 3 | 10 |
| start_delay | R/W | set the start delay. Events between T0 and start_delay will be discarded | 0 |
| bins | R | number of bins of the histogram | |
| max_conts | R | maximum number of counts y-axes on the histogram | |
| buffer_type | R | type of the buffer: (always decoded) |
The bin width is the x-axis bin size in clock cycles. The minimum bin width is 3 clock cycles. The bin width is set with the parameter binwidth. The bin width is used to calculate the time base of the histogram. The time base is calculated as follow:
binwidth * clock_period * index_of_the_bin
For example, if the binwidth is set to 10 and the clock of the board is 100 MHz, each bin will last 100ns.
The start delay is the minimum delay between the T0 and the first event. The start delay is set with the parameter start_delay. Any events before this delay are discarded. The histrogram start after the start delay. In any case, at least one clock cycle between T0 and first event must be present. The start delay is usefull to cut-off for example prompt gamma events or to compensate a delay between the T0 and the expected time of the first event in order to do not waste bins on the hisgram.
The following commands are available:
| Command | Description | Parameter |
|---|---|---|
| start | start the histogram integration | |
| stop | suspend the histogram integration | |
| reset | reinitialize all bins in the histogram to 0 |
start and stop commands do not reset the spectrum. They should be consideder as a start and pause of the spectrum. A start command after a stop command will continue the integration from the last bin value. In order to reset the spectrum it is necessary to use the reset command. The reset command reset all the bins in the histogram to 0.
The ToF spectrum uses the same data structures of the energy spectrum
The data output structure is the following:
The magic field is a 32 bit value that identify the data format. The data field is a pointer to the data buffer. The data buffer is an array of 32 bit values. The number of elements in the array is defined by the total_bins field. The valid_bins field is the number of bins that contains data. The valid_bins field is always equal to total_bins field.
timecode it's the epoch of the readout PC when the data is readout from the fpga. The timecode is expressed in milliseconds.
Data in the data array are the counts of each bin. The first element of the array is the bin with the lowest time. The last element of the array is the bin with the highest time in the spectrum. Each element of the array is a 32 bit value.
| Data Format |
|---|
| bin 0 |
| bin 1 |
| bin 2 |
| ... |
| bin n |
The status of the spectrum is stored in a SCISDK_SPECTRUM_STATUS structure.
The running field is true if the spectrum is running. The completed field is always false.
The progress field is unused.
The peak_max field is the value of the bin with the highest count.
The total_counter field is the total number of counts in the histogram.
The integration_time field is the integration time of the spectrum in milliseconds.
The current version of the library do not report the peak_max, total_counter, integration_time fields. These fields are always 0.
The following example shows how to use the spectrum component.
You can find the labview file for this example here
This example print a spectrum every second. ```c
SCISDK_SPECTRUM_DECODED_BUFFER *obSpectrum;
int res = SCISDK_AllocateBuffer("board0:/MMCComponents/TOF_0", T_BUFFER_TYPE_DECODED, (void**)&obSpectrum, _sdk);
if (res != NI_OK) {
printf("Error allocating buffer\n");
return -1;
}
SCISDK_SetParameterString("board0:/MMCComponents/TOF_0.binwidth", "100",_sdk);
SCISDK_SetParameterString("board0:/MMCComponents/TOF_0.start_delay", "0", _sdk);
SCISDK_ExecuteCommand("board0:/MMCComponents/TOF_0.reset", "", _sdk;
SCISDK_ExecuteCommand("board0:/MMCComponents/TOF_0.start", "", _sdk);
while (1) {
//Just leave in your code of of two of this sleep functions
usleep(1000*1000); // LINUX: sleep for 1s
Sleep(1000); // WINDOWS: sleep for 1s
int res = SCISDK_ReadData("board0:/MMCComponents/TOF_0", (void *)obSpectrum, _sdk);
if (res == NI_OK) {
for (int i = 0; i < obSpectrum->info.valid_bins; i++) {
printf("[%5d] -- %9d\n", i, obSpectrum->data[i]);
}
}
}
SCISDK_FreeBuffer("board0:/MMCComponents/TOF_0", 1, (void**)&obSpectrum, _sdk);
1.9.8