Getting Started with Micriμm’s μC_OS-III Kernel

Renesas Electronics America Inc.
© 2012 Renesas Electronics America Inc. All rights reserved.
Getting Started with Micriμm’s
μC/OS-III Kernel
© 2012 Renesas Electronics America Inc. All rights reserved.2
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Company Logo
HERE
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Agenda
 Introduction
 Lab 1
 Foreground/Background Systems
 Kernel-Based Applications
 Initiating Multitasking
 Lab 2
 Scheduling and Context Switches
 Lab 3
 Additional Kernel Services
 Lab 4

Conclusion
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Introduction
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Class Objectives
 Understand what services a real-time kernel provides
 Learn how to make use of kernel services
 Learn how kernels are implemented

 Gain experience with an actual kernel
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Labs
 Based on µC/OS-III
 Real-time kernel from Micriµm
 Concepts underlying the labs are not µC/OS-III-specific
 Step-by-step instructions are provided for each lab
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A µC/OS-III-Based Application
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Application Code
Micriµm’s Modules
(Portable Code)
Micriµm’s Modules
(Hardware-Specific Code)
Hardware
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µC/LIBµC/CPUµC/OS-III
A µC/OS-III-Based Application (Cont.)
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Application Code
µC/CPUµC/OS-III BSP
Hardware
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Directory Structure
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Workspace files
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e
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Studio
 IDE supporting Renesas MCUs
 Based on Eclipse
 A variety of debugging features
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Lab 1
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Lab 1 Summary
 The kernel is built alongside application code
 A kernel-based application looks much like any other C
program
 Application code interacts with the kernel through API
functions
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Foreground/Background
Systems
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A Foreground/Background Example
int main (void)
{
Perform initializations;
while (1) {
ADC_Read();
SPI_Read();

USB_Packet();
LCD_Update();
Audio_Decode();
File_Write();
}
}
void USB_ISR (void)
{
Clear interrupt;
Read packet;
}
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Background Foreground
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Foreground/Background Benefits
 No upfront cost
 Minimal training required
 Developers don’t need to learn a kernel’s API
 No need to set aside memory resources to accommodate a
kernel
 There is a small amount of overhead associated with a kernel
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Foreground/Background Drawbacks
 Difficult to ensure that each operation will meet its deadline
 All code in the background essentially has the same importance,
or priority
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while (1) {
ADC_Read();

SPI_Read();
USB_Packet();
Service other devices;
}
void ADC_Read (void) {
Initialize ADC;
while (conv_rdy == 0) {
;
}
Process converted value;
}
Potential to delay entire
application
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Foreground/Background Drawbacks
(Cont.)
 High-priority code must be placed in the foreground (in an
ISR)
 Lengthy ISRs can negatively impact system responsiveness
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while (1) {
ADC_Read();
SPI_Read();
USB_Packet();
LCD_Update();
Audio_Decode();
File_Write();
}
void USB_ISR (void) {
Clear interrupt;

Read packet;
}
If a USB packet is received
immediately after this function
returns, the response time will be
lengthy.
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Foreground/Background Drawbacks
(Cont.)
 Problems with multiple developers
 Developers’ efforts must be closely coordinated
 Difficult expansion, even with one developer
 Changes to one portion of the application may negatively
impact the remainder of the code
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Kernel-Based Applications
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A Kernel-Based Example
void AppTaskADC (void *p_arg)
{
while (1) {
ADC_Read();
Sleep for 1 ms;
}
}
void AppTaskUSB (void *p_arg)
{
while (1) {

Wait for signal from ISR;
USB_Packet();
}
}
void AppISRUSB (void)
{
Clear interrupt;
Signal USB Task;
}
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Tasks ISRs
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Kernel Basics
 Application is divided into tasks
 Kernel shares CPU amongst tasks

Developer may assign importance, or priority, to each task
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Template Task
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static void AppTaskExample (void *p_arg)
{
Perform initializations;
while (1) {
Work toward task’s goals;
}
}
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Initiating Multitasking

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Initializing and Starting the Kernel
 Application code must initialize the kernel
 µC/OS-III is typically initialized in main()
 Initialization accomplished through kernel API functions
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OSInit()
 Must be invoked before any kernel services are used
 Initializes data structures
 Creates internal tasks
 Number of tasks depends on configuration
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