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--
when idle =>
if(a_count(12) = ’1’) then -- when board comes out of reset and time delay expired
if(a_count(3) = ’1’) then -- test version, faster for easier simulation
dcm_rst_state <= wait1; -- and both clock inputs present
else
dcm_rst_state <= idle;
end if;
Figure 38. DCM Reset Code Fragment
Another problem encountered on Quixote designs can be when the logic is sparsely used. The 2M and 6M devices are big
chips, and as such can have long paths internally when not much is in there. Adding a few pipeline registers to break up the
long paths can be required to meet timing when the logic is sparse.
The A/D minimum sample rate is 20 MHz. AC performance is seriously compromised at slow rates and it is recommended
that the A/Ds be run at the highest possible sample rate. A simple decimator in the logic is generally used for this and can be
easily implemented to allow the A/Ds to run at high rates even if the data stream does not need the data that fast.
Loading the Logic Image
For the Quixote, usually an EXORMacs format text file must be generated from the output .BIT file produced by the place
and route process. This is done by opening the PROM File Formatter utility from within the ISE and converting the BIT file
into an EXO file. The PROM properties must be set to “byte- wide” and EXORmacs to generate the required EXO file. Once
the properties are set, the .EXO file is generated in the source directory.
To load the new .EXO file into Virtex2, use the logic downloading applet included in the software release. Within the
program, read in the EXO file you wish to use from the host disk, and program the Virtex2. Since the logic is RAM based, it
must be loaded each time the card is powered up. Resets to the card do not require a logic reload. The programming process
depends on the size of the design being loaded, but typically takes less than 10 seconds. Wait until it finishes before doing
anything else.
The logic loading applet features both a Windows user interface and a command-line interface. You may add a link to the
applet within the Windows startup folder specifying the name of an EXO file to automatically load immediately after
Windows boots. See the Applet chapter for more details on the logic loader applet program.
Alternately, the Malibu library baseboard object provides a number of features to to support downloading of EXO logic
images directly from within your Windows application code. These features are useful in situations where the configuration
of the baseboard logic must be changed “on-the fly” -- during the execution of a Host and/or DSP program. See the chapters
on the baseboard software for details on loading the logic in an application.
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