How-To Guides — mvme 1.17.5 documentation

# How-To Guides

## Rate Estimation Setup

This example shows how to use the rate estimation feature built into 1D histograms. Rate estimation works with statistical data that forms an exponential function.

In this example and MDPP-16_SCP is used but any mesytec VME module should work. The rate estimation is setup for channel 8 of the MDPP.

To make use of the rate estimation feature a 1D histogram accumulating the difference between timestamp values of incoming events needs to be created.

Note

For the module to produce timestamps instead of event counter values the register `0x6038` needs to be set to `1`. mvme does this by default for newly created modules in the VME Interface Settings script.

Steps for creating the histogram:

### Timestamp extraction

Add a new Extraction Filter with two filter words to the mdpp16:

    0001 XXXX XX00 1000 XXXX XXXX XXXX XXXX     any
    11XX XXXX XXXX XDDD DDDD DDDD DDDD DDDD     any

The first filter word matches on the data word for channel 8: the prefix `0001` identifies a data word, the pattern `00 1000` is used to select channel 8 specifically.

The second filter word is used to extract the timestamp value. The prefix `11` marks an End of Event word which contains the 30-bit timestamp. Using the `D` character 19-bits of the timestamp value are extracted.

Set the name of the filter to ts_c8 and click Ok to create the filter.

The complete filter will thus match if there was a data word for channel 8 and the event contained a timestamp data word.

### Timestamp calibration

By default the timestamp is generated using the 16 MHz VME SYSCLK. This means the 19-bit timestamp value is in units of 16 MHz.

The goal is to convert the value to µs which is easier to use: 2^{19} / 16 = 2^{19} / 2^{4} = 2^{15} = 32768.

Thus instead of ranging from \left[ 0, 2^{19} \right[ the timestamp should use the range \left[ 0, 2^{15} \right[.

To transform the value create a Calibration Operator by right-clicking inside the L1 Processing tree (or any higher level processing tree) and selecting New -> Calibration. Use the green + button in the top-right corner to add a new user level if necessary.

As input select the ts_c8 node created in the previous step. Keep the default name ts_c8.cal. Type `µs` in the Unit Label field, set Unit Max to `32768` and press the Apply button. Accept the dialog by pressing Ok.

Fig. 45 Timestamp calibration

### Making the previous timestamp available

Next right-click in the L1 Processing tree (or any higher level processing tree) and select New -> Previous Value.

As input select the ts_c8.cal node created in the previous step. Make sure the Keep valid parameters box is checked. Set the name to ts_c8.cal.prev.

Fig. 46 Adding the PreviousValue operator

### Histogramming the timestamp difference

Again right-click in one of the processing trees and choose New -> Difference. Set input A to ts_c8.cal and input B to ts_c8.cal.prev. Set the name to ts_c8.diff.

Fig. 47 Calculating the timestamp difference

Right-click in the display tree below and add a new 1D histogram using the difference ts_c8.diff as the input.

Open the newly created histogram click on Subrange, select Limit X-Axis and enter `(0.0, 200.0)` as the limits. This step limits the large default parameter range calculated by the Difference operator.

Fig. 48 Setting the histogram subrange

Next click the Rate Estimation button in the toolbar and then select two points on the x-axis to use for the rate estimation.

Fig. 49 Rate estimation data and curve visible

The calculation performed is:

\tau &= (x_{2} - x_{1}) / log(y_{1} / y_{2}) \\ y &= y_{1} * (e^{-x / \tau} / e^{-x_{1} / \tau}) \\ freeRate &= 1.0 / \tau

## VM-USB Firmware Update

The VM-USB firmware update functionality can be found in the mvme main window under Tools -> VM-USB Firmware Update. The latest firmware file is included in the mvme installation directory under extras/vm-usb.

Before starting the update set the Prog dial on the VM-USB to one of the programming positions P1-P4.

The controller will start the newly written firmware immediately after writing completes. Reset the Prog dial to C1-C4 to make the controller start the correct firmware on the next power cycle.