Dromajo is a RV64GC functional simulator designed for co-simulation. To use it as a co-simulator, it requires you to pass the committed trace of instructions coming from the core into the tool. Within Chipyard, this is done by connecting to the TracePort` signals that are piped to the top level of the DUT. While the Rocket core does have a TracePort, it does not provide the committed write data that Dromajo requires. Thus, Dromajo uses the ExtendedTracePort only probided by BOOM (BOOM is the only core that supports Dromajo co-simulation). An example of a divergence and Dromajo’s printout is shown below.
[error] EMU PC ffffffe001055d84, DUT PC ffffffe001055d84
[error] EMU INSN 14102973, DUT INSN 14102973
[error] EMU WDATA 00000000000220d6, DUT WDATA 00000000000220d4
[error] EMU MSTATUS a000000a0, DUT MSTATUS 00000000
[error] DUT pending exception -1 pending interrupt -1
Dromajo shows the divergence compared to simulation (PC, inst, inst-bits, write data, etc) and also provides the register state on failure. It is useful to catch bugs that affect architectural state before a simulation hangs or crashes.
To use Dromajo with BOOM, refer to Debugging RTL section on Dromajo.