[profiler] add README.md

profiler/README.md

@@ -0,0 +1,32 @@
+# Usage
+
+## Prepare Prof Input Vcd
+
+This step is integrated into nix build flow.
+
+e.g., the following command will generate prof vcd for case 'codegen.vadd_vv' to directory 'result-prof-vcd'
+```
+nix build --impure .#t1.blastoise.t1rocketemu.run.codegen.vadd_vv.vcs-prof-vcd -o result-prof-vcd
+```
+
+NOTE: only 't1rocketemu' is supported
+
+## Run profiler
+
+```
+nix run .#t1.profiler <INPUT_VCD> <OUTPUT_DIR>
+```
+
+e.g. run `nix run .#t1.profiler result-prof-vcd/*.vcd prof-result`,
+the profiler will generate various analysis results in 'prof-result' directory.
+
+### Disassemble Support
+
+The profiler depends on `spike-dasm` to do disassemble and
+you need to set path of 'spike-dasm' to environment variable `SPIKE_DASM`
+
+```
+export SPIKE_DASM=$(nix build --print-out-paths .#spike)/bin/spike-dasm
+```
+
+If `SPIKE_DASM` is not set, all disassembles in `inst_map.txt` become '<unavail>'.