Hello, this is Bee.
In the previous article, " Selecting a Configuration ROM," we studied configuration mode and understood the reason for configuring in AS mode.
This time, I would like to consider how long it takes from the start to the end of configuration when configuring in AS mode.
As we studied last time, AS mode reads data from EPCS. We know that the configuration data size is device-dependent.
In the case of EP4CE10: rbf file size = 2,944,088bits
So, at what clock frequency is the data being transferred?
First, we decided to check the AS mode connection diagram in the handbook to find out about the clock.
(This can be found under System Integration → Configuration → AS Configuration in the Cyclone® IV Device Handbook.)
The clock supplied from the FPGA to the EPCS was named DCLK, so we searched the handbook and found it described in the following location.
DCLK in AS mode is a fixed value, so DCLK is either 20 MHz or 40 MHz.
Now, how to calculate the configuration time from here...
I found the formula to calculate the configuration time in the handbook!
I used the above formula to calculate the configuration time.
Configuration Time = rbf file sie x DCLK cycles
Worst Case = 2,944,088 bits x 50ns (20MHz) = 147,204,400ns ≒ 147.2ms
Best Case = 2,944,088 bits x 25ns (40MHz) = 73,602,200ns ≒ 73.6ms
However, this is only an approximate value.
Below is a summary of the approximate values for configuration time in AS mode for Cyclone® IV E.
As you can see, the configuration time is proportional to the logic size.
Now we know how long it takes to configure.
When I explained this to my senior staff, they said, "...not enough." What is wrong with the formulas in the handbook?
Apparently, from the time the power is turned on until the user logic begins to operate, several steps are performed in addition to data transfer.
In the world of seconds, it appears that the user logic operation starts immediately after power-on, but the implementation goes through various processes, doesn't it?
In the next article, we will study steps other than data transfer!
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