dft: updating readme to document current status of the tool

Signed-off-by: Felipe Garay <[email protected]>

src/dft/README.md

@@ -12,11 +12,80 @@ A simple DFT insertion consist of the following parts:
 * A scan_enable pin to allow your design to enter and leave the test mode.
 
 
-# Supported Features
+# TCL Commands
 
-TODO
+## set_dft_config
 
 
+```
+set_dft_config [-max_length <int>]
+               [-clock_mixing <string>]
+```
+
+* `-max_length`: The maxinum number of bits that can be in each scan chain.
+* `-clock_mixing`: How architect will mix the scan flops based on the clock driver.
+    * `no_mix`: Creates scan chains with only one type of clock and edge. This
+      may create unbalanced chains.
+    * `clock_mix`: Craetes scan chains mixing clocks and edges. Falling edge
+      flops are going to be stitched before rising edge.
+
+## report_dft_config
+
+```
+report_dft_config
+```
+
+Prints the current DFT configuration to be used by `preview_dft` and
+`insert_dft`.
+
+## preview_dft
+
+```
+preview_dft [-verbose]
+```
+
+Prints a preview of the scan chains that will be stitched by `insert_dft`. Use
+this command to iterate and try different DFT configurations. This command do
+not perform any modification to the design.
+
+* `-verbose`: Shows more information about each one of the scan chains that will
+  be created.
+
+
+## insert_dft
+
+```
+insert_dft
+```
+
+Implements the scan chains into the design by performing the following actions:
+
+1. Scan Replace.
+2. Scan Architect.
+3. Scan Stitch.
+
+The end result will be a design with scan flops connected to form the scan
+chains.
+
+# Example
+
+This example will create scan chains with a max length of 10 bits mixing all the
+scan flops in the scan chains.
+
+```
+set_dft_config -max_length 10 -clock_mixing clock_mix
+report_dft_config
+preview_dft -verbose
+insert_dft
+```
+
+# Limitations
+
+* There are no optimizations for the scan chains. This is a WIP.
+* There is no way to specify existing scan ports to be used by scan insertion.
+* There is currently no way to define a user defined scan path.
+* We can only work with one bit cells.
+
 ## License
 
 BSD 3-Clause License. See [LICENSE](../../LICENSE) file.