Configuration Handbook - Kamami.pl

Enhanced Configuration Devices (EPC4, EPC8 & EPC16) Data Sheetaccess time is ~90 ns). This translates to a flash-read bandwidth of16 bits × 10 MHz = 160 Mbps. Hence, the configuration time is limited bythe flash-read time.When configuration data is compressed, the amount of data that needs tobe read out of the flash is reduced by about 50%. If 16 bits of compresseddata yields 30 bits of uncompressed data, the flash-read bandwidthincreases to 30 bits × 10 MHz = 300 Mbps, reducing overall configurationtime.You can enable the controller's decompression feature in the Quartus IIsoftware, Configuration Device Options window by turning onCompression Mode.1 The decompression feature supported in the enhancedconfiguration devices is different from the decompressionfeature supported by the Stratix II FPGAs and the Cycloneseries. When configuring Stratix II FPGAs or the Cyclone seriesusing enhanced configuration devices, Altera recommendsenabling decompression in Stratix II FPGAS or the Cycloneseries only for faster configuration.The compression algorithm used in Altera devices is optimized for FPGAconfiguration bitstreams. Since FPGAs have several layers of routingstructures (for high performance and easy routability), large amounts ofresources go unused. These unused routing and logic resources as well asun-initialized memory structures result in a large number ofconfiguration RAM bits in the disabled state. Altera's proprietarycompression algorithm takes advantage of such bitstream qualities.The general guideline for effectiveness of compression is the higher thedevice logic/routing utilization, the lower the compression ratio (wherethe compression ratio is defined as the original bitstream size divided bythe compressed bitstream size).For Stratix designs, based on a suite of designs with varying amounts oflogic utilization, the minimum compression ratio was observed to be 1.9or a ~47% size reduction for these designs. Table 2–4 shows sampleAltera Corporation 2–17May 2007 Configuration Handbook, Volume 2