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3. Electronic Ground System Equipment
Adding flag bit
Increasing the width to 47 bits, does not increase the number of used blocks.
Blocks used by FIFO =
5461 words × 47 bit/word
= 13.9 blocks = 14 blocks
18 kbit/blocks
Letting a flag bit indicate whether or not a word is occupied, downloaded words
that are all zeros could be discarded. This relieves the DPU Emulator of checking
how many words to download, thus reducing the effective download duration with
1.25 ms. Using data from chapter 3.4, a new effective transfer rate may be calculated. In addition, bandwidth requirement is reduced from 48 to 47 bits.
In the following calculation, the delay of writing the data to RAM is included to
get a realistic calculation. The number of bytes to download has no uncertainty.
The correct number of byte was used in the calculations, but an approximation is
shown for practical reasons.
Bytes to download
= 5461 words × 47 bit/word≈31.331 kB
Write to buffer
=
Duration of download =
Effective duration
=0.2785 ± 0.0007 ms
31.33 kB
12 MB/s
=2.5 ± 0.4 ms
= (2.5 + 0.2785) ms
Expected transfer rate =
Required transfer rate
Bandwidth utilization
2.331 s
× 31.33 kB
228 B
31.33 kB
2.8 ms
=2.8 ± 0.4 ms
=10.9 ± 1.6 MB/s
=10.36446 ± 0.00011 MB/s
=(95.1 ± 1.4)%
In general, this scheme allows lossless data transfer, however the time margins
are small. A disturbance on the computer may still result in occasional packet
loss.