Hello. This is Ume Onigiri.
I'm Ume Onigiri, and I've been obsessed with "shortening configuration time.
One day, Ume-Onigiri, who has been obsessed with "reducing configuration time," noticed the following.
"If I set the configuration mode to FPP mode and compress the data, the configuration time will be even shorter.
This is probably the strongest combination to reduce the configuration time."
However, an unfortunate fact was discovered.
To my surprise, Cyclone® IV does not support data compression in FPP mode!
The handbook stated the following
Cyclone® IV E does not support data compression, but Cyclone® V does.
So, I thought that the FPP mode and data compression would be a good combination for Cyclone V, and I would be able to reduce the configuration time significantly.
However, I found out that FPP mode and data compression in Cyclone V can reduce configuration time only in a limited number of cases.
When checking the timing waveforms in FPP mode with data compression, one can see that multiple clock cycles are required to transfer a single word.
The number of clocks required to transfer one word depends on the bit width of the data transfer.
Let us consider the case where the rbf file size is 21,061,120 bits.
If the data transfer rate is 8 bits
･No data compression
The number of clocks required for transfer is 21,061,120 ÷ 8 = 2,632,640 clocks
･With data compression (30% reduction)
21,061,120 X 0.7 X 2 ÷ 8 = 3,685,696 clocks required for transfer
･With data compression (55% reduction)
21,061,120 X 0.45 X 2 ÷ 8 = 2,369,376 clocks required for transfer
Depending on the compression ratio, the number of clocks required for data transfer may be higher than without compression.
Therefore, the configuration time will also increase.
If compression reduces the data size to less than 50% of the original size, the configuration time can be reduced.
Incidentally, data size can be reduced by 30% to 55% with compression. (* This depends on the design.)
In case of 16-bit data transfer rate
･No data compression
The number of clocks required for transfer is 21,061,120 ÷ 16 = 1,316,320 clocks
･With data compression (30% reduction)
The number of clocks required for transfer is 21,061,120 X 0.7 X 4 ÷ 16 = 3,685,696 clocks
･With data compression (55% reduction)
21,061,120 X 0.45 X 4 ÷ 16 = 2,369,376 clocks required for transfer
Even at the maximum compression ratio, the number of clocks required for data transfer is lower in the uncompressed case.
In this case, it seems that data compression would certainly increase the configuration time.
Conclusion
In FPP mode, data compression does not reliably reduce configuration time.
I had an easy idea that "as long as data compression is done, configuration time will be reduced."
But this experience made me feel the depth of configuration.
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