Difference between revisions of "Data accumulation rate"
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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: | ||
| − | :< | + | :''S''<sub>w</sub> × (''S''<sub>head</sub> + ''N''<sub>c</sub> × ''N''<sub>RC</sub> × ''N''<sub>rro</sub> + ''S''<sub>chk</sub>) × ''f''<sub>DV</sub> |
| − | |||
where: | where: | ||
| − | * < | + | * ''S''<sub>w</sub> is the word size (=32 bits) |
| − | * < | + | * ''S''<sub>head</sub> is the size (in words) of the [[frame header]] (=43 words) |
| − | * < | + | * ''N''<sub>c</sub> is the number of columns per [[readout card]] (=8) |
| − | * < | + | * ''N''<sub>RC</sub> is the number of readout cards read out (see {{param|cc|rcs_to_report_data}}) |
| − | * < | + | * ''N''<sub>rro</sub> is the number of rows read out (i.e. {{param|cc|num_rows_reported}}) |
| − | * < | + | * ''S''<sub>chk</sub> is the size (in words) of the frame checksum (=1 word) |
| − | + | * ''f''<sub>DV</sub> is the read-out data rate. When in internal-DV mode (i.e. {{param|cc|use_dv}} is zero), this is: | |
| − | + | ::''f''<sub>DV</sub> = 50 MHz / (''N''<sub>dr</sub> × ''N''<sub>r</sub> × ''N''<sub>rl</sub>) | |
| − | < | + | :: ≡ ''f''<sub>ARZ</sub> / ''N''<sub>dr</sub> |
| − | |||
| − | :< | ||
where: | where: | ||
| − | * | + | * 50 MHz is the clock rate |
| − | * < | + | * ''N''<sub>dr</sub> is the number of samples co-added into an output frame (i.e. {{param|cc|data_rate}}) |
| − | * < | + | * ''N''<sub>r</sub> is the number of rows servoed (i.e. {{param|sys|num_rows}}) |
| − | * < | + | * ''N''<sub>rl</sub> is the row dwell-time in clock periods (i.e. {{param|sys|row_len}}), and |
| − | and | + | * ''f''<sub>ARZ</sub> 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: | ||
| − | + | * a single readout card reading 41 rows at 400 Hz is ≈ 0.5 megabytes/second. | |
| − | |||
== Tables == | == Tables == | ||
Latest revision as of 15:20, 5 January 2026
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:
- Sw × (Shead + Nc × NRC × Nrro + Schk) × fDV
where:
- Sw is the word size (=32 bits)
- Shead is the size (in words) of the frame header (=43 words)
- Nc is the number of columns per readout card (=8)
- NRC is the number of readout cards read out (see rcs_to_report_data)
- Nrro is the number of rows read out (i.e. num_rows_reported)
- Schk is the size (in words) of the frame checksum (=1 word)
- fDV is the read-out data rate. When in internal-DV mode (i.e. use_dv is zero), this is:
- fDV = 50 MHz / (Ndr × Nr × Nrl)
- ≡ fARZ / Ndr
where:
- 50 MHz is the clock rate
- Ndr is the number of samples co-added into an output frame (i.e. data_rate)
- Nr is the number of rows servoed (i.e. num_rows)
- Nrl is the row dwell-time in clock periods (i.e. row_len), and
- fARZ 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 ≈ 0.5 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 | |
