The Build System

Author: Lukas Bauer 2024

Integrate a Core/Memu into the piconut toplevel

When creating a new core or memory, it needs to be integrated into the piconut toplevel.

The makesystem provides a way to select different cores and memories to be used in the piconut. For this #ifdef statements are used in the piconut.h file to select the correct core and memory. The name of the define is generated by the makesystem and is the same as the folder name of the core or memory. The format is the folder name in uppercase surrounded by two underscores. For example if the core is in the folder hw/core/my_core the define will be __MY_NUCLEUS__.

In order to integrate a new core or memory into the piconut toplevel the following steps need to be done:

  1. Add an #include statement to the piconut.h file. the #include statement should be inside an #ifdef statement with the name of the core or memory.

#ifdef __MY_NUCLEUS__
#include "my_core.h"
#endif

  1. Add a Instance variable to the SC_MODULE in the piconut.h file. For cores use the varaible name core and for memories use the variable name memu. This also needs to be inside an #ifdef statement with the name of the core or memory.

#ifdef __MY_NUCLEUS__
my_core *core;
#endif

Adding a configuration option to the piconut

To add a configuration option to the piconut, it needs to be added to three different files:

  • hw/piconut/config.mk

  • hw/common/piconut-config.template.h

  • hw/common/Makefile

hw/piconut/config.mk

In the config.mk file, the Option is added as a makefile variable. The option starts with CFG_ followed by the name of the option in uppercase and with underscores instead of spaces. After this a ?= followed by the default value of the option is added. Above the option, a comment must be added to describe the option.

# The option .....
CFG_MY_OPTION ?= 0

hw/common/piconut-config.template.h

This file is used to include the configuration options into the hardware source code. The options are included as #define statements. The name of the option must be the same as in the config.mk file. As a value the name of the option enclosed in curly braces is used. This is used to replace fill in the value of the option during the build process. Each option must have a doxygen comment to describe the option above it.

/**
 * @brief Brief description of the option
 *
 * The option .....
 */
#define CFG_MY_OPTION {CFG_MY_OPTION}

hw/common/Makefile

To use the configuration option in the hardware source code, the piconut-config.h needs to be generated with values from the config.mk file. To do this the sed command at the end of the Makefile in the hw/common needs to be modified. The sed command replaces the curly braces in the piconut-config.template.h file with the values from the config.mk file. For this you need to add a line to the sed command for each configuration option.

	@sed \
	-e 's#{CFG_REGFILE_SIZE}#$(CFG_REGFILE_SIZE)#g' \
    -e 's#{CFG_MY_OPTION}#$(CFG_MY_OPTION)#g' \