Debugging with LiteScope

LiteScope is the logic analyzer of LiteX. Using it next to LiteInjector lets you:

• check the injection: see the probed signals before and after the injector, on the faulted cycle;
• prepare a campaign: find the address of an instruction, or the cycle of an event, to build the trigger;
• debug the emulator itself: its internal signals can be probed like any other signal.

Example

The counter example also adds a LiteScope analyzer. It records the counter signals and the output_hit signal of the trigger system, which is high on the faulted cycles:

analyzer_signals = [
    count_result,
    count_clk_divider,
    injector_output,
    self.injector.trigger.output_hit,
]

self.submodules.analyzer = LiteScopeAnalyzer(analyzer_signals,
    depth   = 512,
    csr_csv = "analyzer.csv")
self.add_csr("analyzer")

Other useful probes are self.injector.trigger.trigger_hit (condition met), self.injector.trigger.inject_start (first faulted cycle), self.injector.injector.sink.data and self.injector.injector.output (data before and after the injector).

To capture the moment of the fault, trigger LiteScope on output_hit, then inject:

$ litex_server --uart --uart-port /dev/ttyUSB1
$ litescope_cli -r main_injector_trigger_output_hit

LiteScope writes a dump.vcd file to open with GTKWave. See the LiteX wiki page Use LiteScope to debug a SoC for more.