Difference between revisions of "Data accumulation rate"

Revision as of 16:05, 15 July 2019

This page gives some rules for estimating the accumulation rate of data on disk for a running MCE.

In general, during a regular acquisition, the data rate (bit rate) of an MCE is:

<math>S_w \times (43 + N_c \times N_r + 1) \times f_{DV}</math>

where:

<math>S_w</math> is the word size (=32 bits)
43 words is the size of the frame header
<math>N_c</math> is the number of columns read (<math>=8 \times N_{RC}</math>, where <math>N_{RC}</math> is the number of readout cards used)
<math>N_{rro}</math> is the number of rows read out (i.e. num_rows_reported)
1 word is the size of the frame footer

<math>f_{DV}</math> is the read-out data rate:

<math>f_{DV} = \frac{50\;\mathrm{MHz}}{ N_{dr} \times N_{r} \times N_{rl} }</math>

where:

<math>N_{dr}</math> is the number of samples co-added into an output frame (i.e. data_rate)
<math>N_{r}</math> is the number of rows servoed (i.e. num_rows)
<math>N_{rl}</math> is the row dwell-time in clock periods (i.e. row_len)

A useful approximation is:

a single readout card reading 41 rows at 400 Hz is <math>\approx0.5</math> megabytes/second.

Here are some tables of accumulation rates for both kinds of subracks for various data rates and numbers of rows:

@@ Line 19: / Line 19: @@
 * <math>N_{dr}</math> is the number of samples co-added into an output frame (i.e. {{param|cc|data_rate}})
 * <math>N_{r}</math> is the number of rows servoed (i.e. {{param|cc|num_rows}})
-* <math>N_{rl}</math> is the row dwell-time (i.e. {{param|cc|row_len}})
+* <math>N_{rl}</math> is the row dwell-time in clock periods (i.e. {{param|cc|row_len}})