Navigate through sea of log messages in a SoC env – smart application of vmm_log

Srinivasan Venkataramanan & Bagath Singh, CVC Pvt. Ltd. Jaya Chelani, Quartics Technologies

Consider an SoC with several interfaces being verified.  It is quite common to have each interface report its activity via display messages.  Now let’s take up a case where-in a specific user is debugging say the AXI interface for failure, performance analysis etc.  While the full log file is providing the overall picture, it is quite possible to get lost quickly in the sea of messages.

Won’t it be nice to have AXI report all its activities to its own log file? This would greatly reduce the analysis/debug time for a given task.  However doing a change inside the testbench is not a good practice, if one were to do it via `ifdef, config etc.  Also, it may be restricted to only few tests/runs, and not for entire regression.

Huh, such a common scenario, you wonder.  Yes, and that’s why vmm_log has that capability built-in.  By default, loggers direct messages to STDOUT, but can be easily asked to direct them to a specific file. The function vmm_log::log_start(file_pointer) performs just this and can be used at will during run time.

1. program automatic sep_log_files;

2.   `include “vmm.sv”

3.   vmm_log axi_logger, cvc_prop_if_logger;

4.   int axi_fp;

5.   initial begin : b1

6.     axi_fp = $fopen (“axi.log”, “w”);

7.     axi_logger = new (“AXI Log”, “0″);

8.     cvc_prop_if_logger = new (“CVC Log”, “0″); // Defaults to STDOUT

9.     axi_logger.log_start(axi_fp); // AXI alone is being sent to a separate LOG file

10.    `vmm_note (axi_logger, “Message from AXI Interface”);

11.    `vmm_note (cvc_prop_if_logger, “Messages from CVC Proprietary Interface”);

12.   end : b1

13.  endprogram : sep_log_files

Line 6 opens a file named “axi.log” for writing. Line 9 ensures that all messages form axi_log to the new log file pointer (created in Line 6). Note that one can point to any logger inside the env via hierarchical path and hence this can be done at a testcase level, if desired.

A few additional notes

1. As these methods work on specific log instance, they ought to be used once the log instance is constructed, typically after the vmm_env::build() phase.

2. There is also a counterpart to stop logging vmm_log::log_stop(file_pointer) to a separate file (it continues sending messages to STDOUT).

3. By design, the vmm_log::log_start() sends a copy of the message to the specified file in addition to STDOUT. This is done so that the complete log (sent to STDOUT) is intact from all loggers in the environment.

4. If it is desired by the user to avoid the duplication of log messages, the user can use an explicit call to vmm_log::log_stop(STDOUT).

5. These two methods can also be useful in performance measurement during a specific time window in a simulation run. One can setup notifiers to indicate the start & stop of the time window, and run a parallel thread to correspondingly perform log_start()  log_stop(). More on this in another blog post.