PULPissimo Testbench

This is the testbench that is used to simulate PULPissimo. It provides three execution modes:

• Load and execute programs through JTAG (boot from JTAG)
• Execute preloaded programs on flash
• Load no program and wait for OpenOCD to connect

JTAG TAPs and Flash

When running tests or developing programs, we normally use the first mode to do that. No special configuration is required to do that, just follow the PULP-SDK documentation. By setting LOAD_L2 to "STANDALONE" or "JTAG" you can boot from flash or via JTAG respectively. Internally this sets the s_bootsel signal accordingly.

Currently we have two JTAG TAPs chained together: the first one is standard compliant JTAG DTM (Debug Transport Module), while the second one is our custom PULP TAP. Both can be used to access the L2 memory to load data into it. The USE_PULP_BUS_ACCESS parameter can be used to choose which one to use. By default we use the PULP TAP because it is much faster in simulation.

OpenOCD

If you wish to interact with the testbench through GDB and OpenOCD you can do this by setting the ENABLE_OPENOCD=1 parameter. Careful OpenOCD and GDB need a long time to establish a connection with the testbench (due to simulation being slow) so timeouts have to be set accordingly.

We recommend to do this with the following steps

1. Compile and run your program using the pulp-sdk with the following command: make conf CONFIG_OPT="vsim/tcl_args=-sv_lib vsim/tcl_args="${VSIM_PATH}"/../rtl/tb/remote_bitbang/librbs vsim/tcl_args=-gENABLE_OPENOCD=1" clean all run

2. If done correctly you get the following message:

   This emulator compiled with JTAG Remote Bitbang client.
   Listening on port 42087
   Attempting to accept client socket
   

   Set now the environment variable JTAG_VPI_PORT to the port the server is listening to by calling export JTAG_VPI_PORT=[portname]. The server will accept commands from openocd redirect those through DPI to the JTAG module in the testbench.

3. Call openocd -f pulpissimo_debug.cfg. After a while you will be prompted with an address you can connect gdb to, normally localhost:3333