Once triggered, the beamloss monitor will store the last 100 ms of the signal before the trigger on a file. This file starts with a header, followed by the ADC values, organized in rows of fixed length. The number of rows, and their length is defined in the header. The numbers are stored binary (Intel) format. The header is defined in the include file shown below. To download this file shift-click here when you use netscape, or right-click here for windows explorer.
#ifndef BLMHDR_H
#include
typedef struct header {
int magic1;
int magic2;
unsigned short version;
short channels;
short oversampling;
short decimation;
unsigned int pre;
unsigned int post;
struct timeval trigtime;
double t0;
double period;
unsigned int nbytes;
int spare[32];
} HEADER;
#define BLMHDR_H
#endif
The header is a structure with a length of 180 bytes, which contains the information to decode the rest of the file. Most variables in this structure will always have the same values, given in brackets below. Integer values in the structure are aligned on 4-byte boundaries, shorts on 2-bytes, and doubles on 8-byte boundaries.
| Variable name | Size | Description | Value |
|---|---|---|---|
| magic1 | int | file identifier | (0x02102001) |
| magic2 | int | second file identifier | (0x1345) |
| version | short | version identifier most significant byte: major, least significant byte: minor |
(0x0100) |
| channels | short | number of active channels | (8) |
| oversampling | short | ADC setting | (1) |
| decimation | short | ADC setting | (4) |
| pre | unsigned int | number of samples before the trigger | (-) |
| post | unsigned int | number of samples after the trigger | (-) |
| trigtime | 2 ints | timestamp of trigger (seconds, µ seconds) | (-) |
| t0 | double | time of first sample with respect to trigger | (-) |
| period | double | time between two samples | (0.768 µ s) |
| nbytes | unsigned int | data length (file excl. header) | (2031616) |
| spare | 32 ints | in version 1.0 not used, uninitialized data! | (-) |
The header is followed by the ADC data. This data is organized in rows of length header.channels (shorts), which is always an even number. There are header.pre + header.post of these rows. Each row contains the data from the ADC for different channels, taken at the same time. The first row contains samples taken header.t0 seconds with respect to the time of the trigger. Each following row is taken header.period seconds later. ADC values are signed numbers in the range [-32484,32484], corresponding to input values in the range -1.03..1.03 V.