⇡ Debug walkthrough

Connecting to RTL simulation and enumeration

Build the RTL simulation

The RTL simulation is a compiled simulation of the entire system with cycle accuracy. You can generate the sources and build the simulation using:

CONFIG=DebugConfig make -C $TOP/vsim sim

The build will take a few minutes.

Start the RTL simulation

Next you can launch the RTL simulation and wait for the debug tool to connect:

$TOP/vsim/DebugConfig-sim +waitdebug

You will see the following output:

Glip TCP DPI listening on port 23000 and 23001

The simulation waits for the Open SoC Debug software to connect.

You may want to debug the system with a waveform (vcd), for which you need to compile a debug simulator and add the +vcd parameters.

# compile a debug simulator
CONFIG=DebugConfig make -C $TOP/vsim sim-debug
# run simulation
$TOP/vsim/DebugConfig-sim-debug +vcd +vcd_name=sim.vcd

The debugger allows you to load a program at run-time but you may want to pre-load a program using the +load parameter.

$TOP/vsim/DebugConfig-sim +load=program

Connect the debug daemon

In a second terminal you can now start the daemon (don’t forget to set up the environment in the second terminal):

opensocdebugd tcp

The daemon will connect using a local TCP connection and run the enumeration of the system, which leads to following output:

Open SoC Debug Daemon
Backend: tcp
System ID: dead
6 debug modules found:
 [0]: HOST
   version: 0000
 [1]: SCM
   version: 0000
 [2]: DEM-UART
   version: 0000
 [3]: MAM
   version: 0000
   data width: 16, address width: 32
   number of regions: 1
     [0] base address: 0x0000000040000000, memory size: 65536 Bytes
     [1] base address: 0x0000000080000000, memory size: 134217728 Bytes
 [4]: CTM
   version: 0000
 [5]: STM
   version: 0000
Wait for connection

You can see the system identifier (dead) and that six modules were found. Each module is listed by the type and the version. For the Memory Access Module (MAM) extra information is available, namely the data and address width and the available memory regions. Thats all the daemon does, it then waits for a tool to connect.

On the first terminal (simulation) you can see that the daemon has connected:

Client connected

You are now ready to actually debug the system and software running in it.

  Debug walkthrough
  A debug session