Manual Smart Placement

Table of Contents

• Introduction
• Steps involved in applying smart placement.
  • Identification of function criticality
  • Priority Assignment
• Function Annotation
• Linker update
• Basic Smart Placement Example

Introduction

This page goes over how to use manual smart placement. Manual smart placement goes with the assumption that the information on function criticality is already known by the developer.

Steps involved in applying smart placement.

In general, there are following steps involved in applying smart placement:

1. Identification of function criticality.
2. Priority Assignment.
3. Function Annotation.
4. Linker update.

Identification of function criticality

Here, the developer needs to decide what all functions in the application are critical.

Priority Assignment

Once critical functions are identified, now it is required to put a priority function. For Manually identified functions, it is known that they are critical functions. So, we can start with assigning highest priority.

Note

Lower number corresponds to higher priority. Priority and Priority Number are both different. A highest Priority function would have lowest Priority Number.

Here, function with lower priority number will be placed by the linker in the faster memory first.

Function Annotation

Compiler provides a feature where any function can be annotated which is essentially controlling its placement in memory.

C/C++ Source-level function attributes:

__attribute__(({local,onchip,offchip}(priority)))

Here local, onchip and offchip are corresponding to TCMx, MSRAM/OCRAM, FLASH.

Example:

void __attribute__((local(1))) func0(void) { .. } // Place in TCM with priority 1

void __attribute__((local(2))) func1(void) { .. } // Place in TCM with priority 2

void __attribute__((onchip)) func2(void) { .. } // Place in MSRAM/OCRAM with implied priority 1

The attributes can be added to a function definition or a function declaration (if that function is called/referenced in the same compilation unit).

Assembly metainfo directives:

Functions can also be annotated by adding an assembly metainfo directive in an assembly file that is compiled and linked with the project using the following format:

  .global <global function symbol>

  .sym_meta_info <global function symbol>, “of_placement”, {“local”,”onchip”,”offchip”}, <priority>

e.g.

.global strcmp

.sym_meta_info strcmp, “of_placement”, “local”, 1

Here in C, strcmp is the symbol name given to function strcmp.

This would allow users to avoid having to compile 3rd party source code.

Linker update

Please go through Changes in linker for Smart Placement document to do relevant changes.

Note

Although these changes are already at-least in Memory Benchmark with Smart Placement SDK examples. So, changes can be copied and pasted directly from the empty example and any more changes can be done on top of that.

Basic Smart Placement Example

Basic Smart Placement

This example provides a basic overview of applying smart placement and compares run time of functions with smart placement and without smart placement.

The Aim of this example is to:

1. Showcase the process of smart placement in simple terms.
2. How Smart Placement improves code performance?
3. How Cache Miss ratio is improved?