last edited: 2023-06-07 20:25:00 +0000
Building the MSI protocol
The SLICC file
Now that we have finished implementing the protocol, we need to compile it. You can download the complete SLICC files below:
Before building the protocol, we need to create one more file:
MSI.slicc
. This file tells the SLICC compiler which state machine
files to compile for this protocol. The first line contains the name of
our protocol. Then, the file has a number of include
statements. Each
include
statement has a file name. This filename can come from any of
the protocol_dirs
directories. We declared the current directory as
part of the protocol_dirs
in the SConsopts file
(protocol_dirs.append(str(Dir('.').abspath))
). The other directory is
src/mem/protocol/
. These files are included like C++h header files.
Effectively, all of the files are processed as one large SLICC file.
Thus, any files that declare types that are used in other files must
come before the files they are used in (e.g., MSI-msg.sm
must come
before MSI-cache.sm
since MSI-cache.sm
uses the RequestMsg
type).
protocol "MSI";
include "RubySlicc_interfaces.slicc";
include "MSI-msg.sm";
include "MSI-cache.sm";
include "MSI-dir.sm";
You can download the fill file here.
Compiling a protocol with SCons
Most SCons defaults (found in build_opts/
) specify the protocol as
MI_example
, an example, but poor performing protocol. Therefore, we
cannot simply use a default build name (e.g., X86
or ARM
). We have
to specify the SCons options on the command line. The command line below
will build our new protocol with the X86 ISA.
scons build/X86_MSI/gem5.opt --default=X86 PROTOCOL=MSI SLICC_HTML=True
This command will build gem5.opt
in the directory build/X86_MSI
. You
can specify any directory here. This command line has two new
parameters: --default
and PROTOCOL
. First, --default
specifies
which file to use in build_opts
for defaults for all of the SCons
variables (e.g., ISA
, CPU_MODELS
). Next, PROTOCOL
overrides any
default for the PROTOCOL
SCons variable in the default specified.
Thus, we are telling SCons to specifically compile our new protocol, not
whichever protocol was specified in build_opts/X86
.
There is one more variable on this command line to build gem5:
SLICC_HTML=True
. When you specify this on the building command line,
SLICC will generate the HTML tables for your protocol. You can find the
HTML tables in <build directory>/mem/protocol/html
. By default, the
SLICC compiler skips building the HTML tables because it impacts the
performance of compiling gem5, especially when compiling on a network
file system.
After gem5 finishes compiling, you will have a gem5 binary with your new
protocol! If you want to build another protocol into gem5, you have to
change the PROTOCOL
SCons variable. Thus, it is a good idea to use a
different build directory for each protocol, especially if you will be
comparing protocols.
When building your protocol, you will likely encounter errors in your SLICC code reported by the SLICC compiler. Most errors include the file and line number of the error. Sometimes, this line number is the line after the error occurs. In fact, the line number can be far below the actual error. For instance, if the curly brackets do not match correctly, the error will report the last line in the file as the location.