Difference between revisions of "Data accumulation rate"

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This page gives some rules for estimating the accumulation rate of data on disk for a running MCE.
 
This page gives some rules for estimating the accumulation rate of data on disk for a running MCE.
  
 +
== Rate calculations ==
 
In general, during a regular acquisition, the data rate (bit rate) of an MCE is:
 
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>
+
:<math>S_w \times (S_{head} + N_c \times N_{RC} \times N_{rro} + S_{chk}) \times f_{DV}</math>
  
 
where:
 
where:
 
* <math>S_w</math> is the word size (=32 bits)
 
* <math>S_w</math> is the word size (=32 bits)
* 43 words is the size of the frame header
+
* <math>S_{head}</math> is the size (in words) of the [[frame header]] (=43 words)
* <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 card]]s used)
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* <math>N_c</math> is the number of columns per [[readout card]] (=8)
 +
* <math>N_{RC}</math> is the number of readout cards read out (see {{param|cc|rcs_to_report_data}})
 
* <math>N_{rro}</math> is the number of rows read out (i.e. {{param|cc|num_rows_reported}})
 
* <math>N_{rro}</math> is the number of rows read out (i.e. {{param|cc|num_rows_reported}})
* 1 word is the size of the frame footer
+
* <math>S_{chk}</math> is the size (in words) of the frame checksum (=1 word)
  
  
<math>f_{DV}</math> is the read-out data rate:
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<math>f_{DV}</math> is the read-out data rate.  When in internal-DV mode (i.e. {{param|cc|use_dv}} is zero), this is:
  
:<math>f_{DV} = \frac{50\;\mathrm{MHz}}{ N_{dr} \times N_{r} \times N_{rl} }</math>
+
:<math>f_{DV} = \frac{50\;\mathrm{MHz}}{ N_{dr} \times N_{r} \times N_{rl} } \equiv \frac{f_{ARZ}}{N_{dr}}</math>
 
where:
 
where:
 +
* <math>50\;\mathrm{MHz}</math> is the clock rate
 
* <math>N_{dr}</math> is the number of samples co-added into an output frame (i.e. {{param|cc|data_rate}})
 
* <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_{r}</math> is the number of rows servoed (i.e. {{param|sys|num_rows}})
* <math>N_{rl}</math> is the row dwell-time in clock periods (i.e. {{param|cc|row_len}})
+
* <math>N_{rl}</math> is the row dwell-time in clock periods (i.e. {{param|sys|row_len}})
 +
and
 +
* <math>f_{ARZ}</math> is the Address-return-to-zero rate, i.e. the frequency at which a single pixel is visited
  
  

Latest revision as of 16:36, 15 July 2019

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

Rate calculations

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

<math>S_w \times (S_{head} + N_c \times N_{RC} \times N_{rro} + S_{chk}) \times f_{DV}</math>

where:

  • <math>S_w</math> is the word size (=32 bits)
  • <math>S_{head}</math> is the size (in words) of the frame header (=43 words)
  • <math>N_c</math> is the number of columns per readout card (=8)
  • <math>N_{RC}</math> is the number of readout cards read out (see rcs_to_report_data)
  • <math>N_{rro}</math> is the number of rows read out (i.e. num_rows_reported)
  • <math>S_{chk}</math> is the size (in words) of the frame checksum (=1 word)


<math>f_{DV}</math> is the read-out data rate. When in internal-DV mode (i.e. use_dv is zero), this is:

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

where:

  • <math>50\;\mathrm{MHz}</math> is the clock rate
  • <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)

and

  • <math>f_{ARZ}</math> is the Address-return-to-zero rate, i.e. the frequency at which a single pixel is visited


A useful approximation is:

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

Tables

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

MCE data accumulation rate in Megabits per second (Mbps)
  48HP   72HP
100 Hz 150 Hz 200 Hz 400 Hz 100 Hz 150 Hz 200 Hz 400 Hz
25 rows 1.28 1.92 2.56 5.12 2.56 3.84 5.12 10.24
33 rows 1.69 2.53 3.38 6.76 3.38 5.07 6.76 13.52
41 rows 0.94 1.42 1.89 3.78 1.42 2.83 3.78 7.56


MCE data accumulation rate in Gigabytes (109 bytes) per hour
  48HP   72HP
100 Hz 150 Hz 200 Hz 400 Hz 100 Hz 150 Hz 200 Hz 400 Hz
25 rows 0.58 0.86 1.15 2.30 1.15 1.73 2.30 4.61
33 rows 0.76 1.14 1.52 3.04 1.52 2.28 3.04 6.08
41 rows 2.10 3.15 4.20 8.40 4.20 6.30 8.40 16.79


MCE data accumulation rate in Gigabytes (109 bytes) per day
  48HP   72HP
100 Hz 150 Hz 200 Hz 400 Hz 100 Hz 150 Hz 200 Hz 400 Hz
25 rows 13.8 20.7 27.7 55.3 27.7 41.5 55.3 110.6
33 rows 18.1 27.4 36.5 73.0 36.5 54.7 73.0 146.0
41 rows 22.7 34.0 45.3 90.7 45.3 68.0 90.7 181.4