How to reduce the size of Nios® V applications

Introduction

This article describes how to reduce the software size used by the Nios^® V processor (hereafter referred to as Nios^® V), which is based on RISC-V architecture.

The Nios^® II processor (hereafter referred to as Nios® II) will be released in winter 2023 (Quartus® Prime Pro v23.4, Quartus^® Prime Standard v23.1) and will be the last soft-core processor to be released, so if you are using a newer version, you should consider using the Nios® V processor. If you wish to use a newer version, you will need to migrate to Nios^® V.

If software size is an issue when migrating from Nios^® II to Nios^® V, please review the information presented in this article.

NOTES:

The methods described in this article affect the post-compilation assembler and may differ from what the user expects when running the application. If you intend to use this method, please verify it thoroughly on your own side before considering its use.

Point:

The Nios^® V application build environment consists of two projects: BSP (Board Support Package) and APP (Application). The settings for size reduction are also different for each project.

1. how to reduce software in the application project

The following article describes how to reduce software in an application project.

Reference : Nios^® V Debug Methodology: Changing the Optimization Level

2. how to reduce software in BSP project

2-1. check box option settings in BSP-Editor

The options introduced in this section are options that can be enabled/disabled by checkboxes in BSP-Editor.

2-2. setting the Cflags option of BSP-Editor

The options introduced in this section are options that can be freely set by the user as compiler flags.

Conclusion

This article has shown how to reduce software size in Nios^® V. We hope you will find it useful when porting software from Nios^® II.

For more information on the Nios^® V processor, please refer to the manufacturer's page below.

Reference: Nios^® V Processor Developer Center

We have also compiled information on Nios^® V in the "Nios® V Processor Developer Center". Nios^{® V} V Summary Page which contains information on Nios® V. Please check this page as well, as it contains useful information in addition to this article.

Related to

Common Setting
Option Name	Option name Summary Description
enable_reduced_device_drivers	This option is effective for IPs that have drivers in reduced size mode. It reduces the code size.

enable_sim_optimize	Enables optimizations to speed up HDL simulation, such as initializing the cache, clearing .bss sections, omitting long delay loops, etc.

use_picolibc	Enabling this option changes the library used from Newlibc to the smaller Picolibc.

Advanced Settings
Option Name	Summary
enable_lightweight_device_driver_api	The function to assign device names to file descriptors (e.g. /dev/uart0) is removed, reducing the driver code and data size. open(), close(), and lseek() routines will no longer function, so use with caution.

Common Settings
Option Name	Overview
cflags_debug	Specifies compiler flags. Specifying -g enables debugging using the debugger. If omitted, debug symbols are removed from the ELF file.

cflags_optimaization	Specifies the level of compiler optimization when Build Type is Release. Use "-O0" for debugging; the default for Relase Type is "-O2".

Advanced Settings
Option Name	Summary
cflags_user_flags	S files, you can set flags that are passed to the compiler when compiling C, C++, and . It is effective to write commands related to removing unused code and unused data, such as -ffunction-sections -fdata-sections

cflags_cxx_flags	You can set flags that are valid when compiling C++. Like cflags_user_flags, -ffunction-sections -fdata-sections and other commands related to removing unused code and unused data are effective.

cflags_link_flags	You can set flags that are effective when the linker is executed. It is effective to write commands related to deletion of unused sections, such as --gc-sections.