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Unable to constrain bidirectional port.

Altera_Forum
Honored Contributor II
940 Views

I have a module that is used to control the operation of an I[SUP]2[/SUP]C bus. One of the outputs in the module is a bidirectional SDA line. I've attempted to constrain the design using the SDC commands: 

 

set_output_delay -clock i2c_clk -min 0.0 set_output_delay -clock i2c_clk -max 0.0 set_input_delay -clock i2c_clk -max 0.0 set_input_delay -clock i2c_clk -min 0.0  

 

where i2c_clk is created with: 

 

create_generated_clock -source -divide_by 126 -name i2c_clk  

 

CLOCK_50 is a 50MHz input clock and {i2c:i2c_inst|i2c_clk} comes from the fact that my design instantiates the i2c module in a top level module. 

 

The output delay seems to work fine. However, I'm getting errors associated with the input delay: "Warning (332174): Ignored filter at lab03.sdc(22): FGPA_I2C_SDAT could not be matched with a port" and "Warning (332049): Ignored set_input_delay at lab03.sdc(22): Argument <targets> is an empty collection". I thought this may have been an issue because I am specifying both input and output delays on the same port, but when I comment out the output delays I get the same error. Additionally, when I run TimeQuest to see the unconstrained input ports, it gives "FPGA_I2C_SDAT" (i.e. exactly the same as input I'm trying to constrain). 

 

I noticed in Ryan Scoville's TimeQuest User Guide on page 114 that internal clocks should not be used to constrain IO ports. However, if I try it with a virtual clock of the same frequency I get the same error. 

 

If any of this is unclear let me know and I'll clarify/post more code. Thanks in advance.
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2 Replies
Altera_Forum
Honored Contributor II
178 Views

 

--- Quote Start ---  

I have a module that is used to control the operation of an I[SUP]2[/SUP]C bus. One of the outputs in the module is a bidirectional SDA line. I've attempted to constrain the design using the SDC commands: 

 

set_output_delay -clock i2c_clk -min 0.0 set_output_delay -clock i2c_clk -max 0.0 set_input_delay -clock i2c_clk -max 0.0 set_input_delay -clock i2c_clk -min 0.0  

 

where i2c_clk is created with: 

 

create_generated_clock -source -divide_by 126 -name i2c_clk  

 

CLOCK_50 is a 50MHz input clock and {i2c:i2c_inst|i2c_clk} comes from the fact that my design instantiates the i2c module in a top level module. 

 

The output delay seems to work fine. However, I'm getting errors associated with the input delay: "Warning (332174): Ignored filter at lab03.sdc(22): FGPA_I2C_SDAT could not be matched with a port" and "Warning (332049): Ignored set_input_delay at lab03.sdc(22): Argument <targets> is an empty collection". I thought this may have been an issue because I am specifying both input and output delays on the same port, but when I comment out the output delays I get the same error. Additionally, when I run TimeQuest to see the unconstrained input ports, it gives "FPGA_I2C_SDAT" (i.e. exactly the same as input I'm trying to constrain). 

 

I noticed in Ryan Scoville's TimeQuest User Guide on page 114 that internal clocks should not be used to constrain IO ports. However, if I try it with a virtual clock of the same frequency I get the same error. 

 

If any of this is unclear let me know and I'll clarify/post more code. Thanks in advance. 

--- Quote End ---  

 

 

First: I have never seen any examples of bidirectional io sdc in the entire pile of Altera timequest documents or its associates. 

Second: I suggest you try -add or -add_delay to input set. 

Third: your observation about input ports not recognized is strange. You know it exists and the tool does as well so somebody in Altera team of software must have a bug or your observation is wrong.
Altera_Forum
Honored Contributor II
178 Views

Yes, you need -add_delay for the input delays to allow for both input and output delays to be attached to the same port. 

 

When you commented out the output delays, did you regenerate the timing netlist? If you didn't, it will still be using the output delays and show the same error.
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