Functional Description
Page 19
The general guideline for effectiveness of compression is the higher the device logic or
routing utilization, the lower the compression ratio (where the compression ratio is
defined as the original bitstream size divided by the compressed bitstream size).
For Stratix designs, based on a suite of designs with varying amounts of logic
utilization, the minimum compression ratio was observed to be 1.9 or a ~47% size
reduction for these designs. Table 6 lists sample compression ratios from a suite of
Stratix designs. These numbers serve as a guideline, not a specification, to help you
allocate sufficient configuration memory to store compressed bitstreams.
(1)
Table 6. Stratix Compression Ratios
Item
Logic Utilization
Minimum
98%
Average
64%
Compression Ratio
% Size Reduction
Note to Table 6:
1.9
2.3
47%
57%
(1) These numbers are preliminary. They are intended to serve as a guideline, not a specification.
Programmable Configuration Clock
The configuration clock (DCLK) speed is user programmable. One of two clock sources
can be used to synthesize the configuration clock; a programmable oscillator or an
external clock input pin (EXCLK). The configuration clock frequency can be further
synthesized using the clock divider circuitry. This clock can be divided by the N
counter to generate your DCLKoutput. The N divider supports all integer dividers
between 1 and 16, as well as a 1.5 divider and a 2.5 divider. The duty cycle for all clock
divisions other than non-integer divisions is 50% (for the non-integer dividers, the
duty cycle will not be 50%). Figure 5 shows a block diagram of the clock divider unit.
Figure 5. Clock Divider Unit
Configuration Device
Clock Divider Unit
External Clock
(Up to 100 MHz)
Divide
by N
DCLK
10 MHz
33 MHz
50 MHz
66 MHz
Internal Oscillator
The DCLKfrequency is limited by the maximum DCLKfrequency the FPGA supports.
f For more information about the maximum DCLKinput frequency supported by the
FPGA, refer to the configuration chapter in the appropriate device handbook.
January 2012 Altera Corporation
Enhanced Configuration (EPC) Devices Datasheet
ALTERA [ ALTERA CORPORATION ]
