How to change EMT thresholds
IMPORTANT: if you have not been
authorised to change the thresholds then don't touch. Call an EMT expert
instead.
The EMT configuration is at present performed via flat files located
in /nfs/bbr-srv02/dataflow/constants/emt.
One of these files, with the filename runXXXX.ax, contains configuration
data for the algorithm xilinx, including information about the EMT thresholds.
There are lots of such files in the area, called runXXXX.ax. The one
that is read on configuration is actually a link called aaaalink.ax which
points to the latest runXXXXax file.
How to change the .ax configuration file
1) Copy the file pointed at by aaaalink.ax to a new file called runXXXX.ax,
where XXXX will be the run number of the first run with the new configuration.
2) Edit the file runXXXX.ax (see below) to set the new thresholds
3) Delete the link aaaalink.ax and remake it to point to your new runXXXX.ax
file. Do not delete the old runXXXX.ax file.
4) Check that the EMT will configure. The actionof configuring will
pick up the new offsets - there is no need to reboot the rom or power cycle
the crate.
5) In the emt xyplex window (xyplex odf-emt), check that the new constants
are what you expect. Type AxSprint after configuration
to check that the constants are what you expect.There will be quite a few
lines of output. Look for the lines
Global M Threshold = 256
Global G Threshold = 768
Global E Threshold = 1920
Global X Threshold = 256
Global Y Threshold = 2304
(or similar) and check that the values on the RHS are what you expect
(see below). The values you get here are counts in decimal.
7) Make a note in the trigger,emt and central BaBar logbooks of what
you have changed, and the number of the first run for which it will take
effect (ie the number in the name of the ax file). Post a trigger
operations hypernews.
How to set the thresholds in the .ax file
The file runXXXX.ax should look something like the following:
0000 000e 000e 000e 000e 000e 000e 000e
6000
0900 0100 0780 0300 0100
0040 0080 0100 0200 0400 0800 1000
0001 0000 fffe 0000 0000 0000 0000 0000
0080 0080 0080 0080 0080 0080 0080 0080
077e
The row of numbers in red are the trigger thresholds. Note that these
numbers are counts from the calorimeter and are in
HEX. The actual threshold in MeV is this number of counts multiplied by ~0.4 MeV. So
for example 100 is 256 decimal x 0.4 MeV ie approximately 100 MeV. Do
not be fooled into thinking these numbers correspond directly to the energy
in MeV.
The five numbers in this row give the five thresholds
Y, X, E, G, M (note the reverse order!).
So in this example the thresholds are:
Y: 0x900 = 2304 decimal = ~1 GeV
X: 0x100 = 256 decimal = ~100 MeV
E: 0x780 = 1920 decimal = ~800 MeV
G: 0x300 = 768 decimal = ~300 MeV
M: 0x100 = 256 decimal = ~100 MeV
So when you type AxSprint in the xyplex window
after configuring the trigger, the decimal values corresponding to your
hex numbers in the file pointed to by aaaalink.ax should be displayed.
After making a change always perform this
check to make sure you haven't made a mistake. And always make a careful
note of what you have done in the trigger logbooks and central BaBar logbook.
If you are not absolutely certain what you are
doing, contact an EMT expert.
Jason McFall, 26 May 1999
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