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. | ||
− | In general, during a regular acquisition, the data rate of an MCE is: | + | == Rate calculations == |
+ | In general, during a regular acquisition, the data rate (bit rate) of an MCE is: | ||
− | :<math>S_w \times N_c \times | + | :<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) | ||
− | * <math>N_c</math> is the number of columns read (<math>= | + | * <math>S_{head}</math> is the size (in words) of the [[frame header]] (=43 words) |
− | * <math> | + | * <math>N_c</math> is the number of columns per [[readout card]] (=8) |
− | * <math> | + | * <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>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. {{param|cc|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. {{param|cc|data_rate}}) | ||
+ | * <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|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 | ||
+ | |||
A useful approximation is: | A useful approximation is: |
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:
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 |
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 |
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 |