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Altera_Forum
Honored Contributor I
887 Views

DE0-NANO Board SDC file and PLL

Hallo 

 

I have a DE0-NANO board. There is a on board 50 MHz oscillator on the board which works as the clock to the FPGA. Now suppose i want to run my design at 30 MHz. So i write a SDC file like the following, would this work? I mean would this already create a pll which will run my design at 33 MHz when i download it on the FPGA? 

# Constrain clock port clk with a 30-ns requirement 

 

 

create_clock -period 33 [get_ports clk] 

 

# Automatically apply a generate clock on the output of phase-locked loops (PLLs) # This command can be safely left in the SDC even if no PLLs exist in the design 

 

 

derive_pll_clocks 

 

 

derive_clock_uncertainty 

 

# Constrain the input I/O path 

 

 

set_input_delay -clock clk -max 0.5 [all_inputs] 

 

 

set_input_delay -clock clk -min 0.1 [all_inputs] 

 

# Constrain the output I/O path 

 

 

set_output_delay -clock clk -max 0.5 [all_outputs] 

 

 

set_output_delay -clock clk -min 0.1 [all_outputs]
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1 Reply
Altera_Forum
Honored Contributor I
74 Views

Changing the SDC file will not change the FPGA design or the board or the behaviour of any of the components on the board. There is a fixed 50MHz oscillator on the Nano. 

 

If you want to run everything at 30MHz then you either need to de-solder 50MHz oscillator and replace it with a 30MHz part - don't do this - or, far more practically, use one of the PLLs in your FPGA to generate the 30MHz clock from the 50MHz. Use the IP catalogue in Quartus to locate a PLL and configure it to your needs. Then instantiate it in your design. 

 

The 'derive_pll_clocks' in your SDC file will then deal with everything required to check that the design will run at the revised frequency. 

 

Cheers, 

Alex
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