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net_analysis.md

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Net Sensitivity Analysis

In the utils directory you will find a script called net_analysis.py which can be used to retrieve all bits which affect the routing of the given net(s). This information can give users insight about which signals in the design are likely to be affected by bit upsets that cause opens and shorts in interconnect tiles.

Input file format

The format that this script accepts as input is a simple line-seperated .txt file. Include the hierarchical names of each net to be anyalzed on seperate lines, like so:

module/net_1
module/net_2

A design checkpoint .dcp post-implementation is also required as an input to the script.

How to use

  1. Activate the BFAT virtual environment and source Vivado
  2. Run the script with the following command:
python3 analyze_nets.py <dcp_file> <nets_file>

Optional Flags:

  • The -a flag specifies that instead of a nets file, all nets in the design should be analyzed. This will take a long time for large designs.
    • If this flag is used, do not put anything in the <nets_file> positional argument
  • The -rpd will specify that the analysis should be performed using RapidWright instead of Vivado for design querying
  • The -g flag will plot a simple histogram of the analyzed data. The bins are organized by the number of sensitive bits per net.
  • The -p flag will export a data structure containing the final analysis in a .pickle file format.
    • This is useful if you want to later make adjustments to a large data set which took a long time to generate (e.g. using the -ntmr flag to only include non-triplicated nets in the analysis file)
  • The -pi flag is used to specify that a previously generated .pickle file is being used instead of a nets file.
    • The full analysis will be skipped in this case, allowing you to generate a plot or perform other operations on the final data more quickly.
  • The -ntmr flag will filter out all triplicated nets with the given TMR prefix.
    • This is useful since errors triplicated nets from TMR tools are already being mitigated, so the sensitivity of these nets is less important.
  • The -of flag can be optionally used to specify the filename and path of the output file

A .txt file containing the results of the analysis will be generated in the same directory that the script was run in with a generated name (or with the name specified with the -of flag)

Output file format

Here is an example entry in the analysis report for a net:

clk_IBUF_BUFG
Pips: (2)
	INT_R_X3Y13/INT_R.GCLK_B11->>CLK0 - CLK0 5-16 Routing Mux:
		Row Bits: ['bit_00400180_026_26', 'bit_00400181_026_28', 'bit_00400180_026_21', 'bit_00400180_026_22']
		Column Bits: ['bit_00400180_026_25', 'bit_00400181_026_20', 'bit_00400181_026_21', 'bit_00400181_026_24']

	INT_R_X3Y12/INT_R.GCLK_B11->>CLK1 - CLK1 5-16 Routing Mux:
		Row Bits: ['bit_00400180_024_30', 'bit_00400180_024_23', 'bit_00400181_024_22', 'bit_00400181_024_25']
		Column Bits: ['bit_00400180_024_27', 'bit_00400180_024_29', 'bit_00400181_024_26', 'bit_00400181_024_29']

Total config bits: 16

The net given is a clock signal which uses two interconnect pips in total. Included in the analysis is the name of each pip, along with the name and type of the pip's routing mux. Lastly, the relevant configuration bits for the routing mux are given, sorted by their row/column encoding.

At the end of the net's section in the report, the total number of unique bits which affect the net's routing is given.

After all of the nets' analyses, some simple summary statistics about the analyzed data are printed.