Renesas Electronics America Inc. “© 2010 Renesas Electronics America Inc. All rights reserved.”...

Renesas Electronics America Inc.

“© 2010 Renesas Electronics America Inc. All rights reserved.”

ID 720L: Software Development with an Open Source Real-Time Operating System

Fatih PeksenarSenior Manager, Applications Engineering

14 October 2010

Version: 1.1

2 “© 2010 Renesas Electronics America Inc. All rights reserved.”

Mr. Fatih Peksenar

Manager, Applications Engineering

Responsible for integrated firmware

development environment framework

within the Renesas America Applications Group.

Ported FreeRTOS to various Renesas platforms.

Examples are: RSKH8S1668, RSKSH7216,

RSKRX62N, RDKRX62N

PREVIOUS EXPERIENCE:

Lead software engineer for telecom companies where used

various RTOS frameworks including: VxWorks, eCos, MQX,

and other home grown kernels

MSEE from the University of Minnesota


Renesas Technology and Solution Portfolio

Microcontrollers& Microprocessors

#1 Market shareworldwide *

Analog andPower Devices#1 Market share

in low-voltageMOSFET**

Solutionsfor

Innovation

Solutionsfor

InnovationASIC, ASSP& Memory

Advanced and proven technologies

* MCU: 31% revenue basis from Gartner "Semiconductor Applications Worldwide Annual Market Share: Database" 25 March 2010

** Power MOSFET: 17.1% on unit basis from Marketing Eye 2009 (17.1% on unit basis).


4

Renesas Technology and Solution Portfolio

Microcontrollers& Microprocessors

#1 Market shareworldwide *

Analog andPower Devices#1 Market share

in low-voltageMOSFET**

ASIC, ASSP& Memory

Advanced and proven technologies

* MCU: 31% revenue basis from Gartner "Semiconductor Applications Worldwide Annual Market Share: Database" 25 March 2010

** Power MOSFET: 17.1% on unit basis from Marketing Eye 2009 (17.1% on unit basis).

Solutionsfor

Innovation

Solutionsfor

Innovation


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Microcontroller and Microprocessor Line-up

Superscalar, MMU, Multimedia Up to 1200 DMIPS, 45, 65 & 90nm process Video and audio processing on Linux Server, Industrial & Automotive

Up to 500 DMIPS, 150 & 90nm process 600uA/MHz, 1.5 uA standby Medical, Automotive & Industrial

Legacy Cores Next-generation migration to RX

High Performance CPU, FPU, DSC

Embedded Security

Up to 10 DMIPS, 130nm process350 uA/MHz, 1uA standbyCapacitive touch

Up to 25 DMIPS, 150nm process190 uA/MHz, 0.3uA standbyApplication-specific integration

Up to 25 DMIPS, 180, 90nm process 1mA/MHz, 100uA standby Crypto engine, Hardware security

Up to 165 DMIPS, 90nm process 500uA/MHz, 2.5 uA standby Ethernet, CAN, USB, Motor Control, TFT Display

High Performance CPU, Low Power

Ultra Low PowerGeneral Purpose


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Microcontroller and Microprocessor Line-up

Superscalar, MMU, Multimedia Up to 1200 DMIPS, 45, 65 & 90nm process Video and audio processing on Linux Server, Industrial & Automotive

Up to 500 DMIPS, 150 & 90nm process 600uA/MHz, 1.5 uA standby Medical, Automotive & Industrial

Legacy Cores Next-generation migration to RX

High Performance CPU, FPU, DSC

Embedded Security

Up to 10 DMIPS, 130nm process350 uA/MHz, 1uA standbyCapacitive touch

Up to 25 DMIPS, 150nm process190 uA/MHz, 0.3uA standbyApplication-specific integration

Up to 25 DMIPS, 180, 90nm process 1mA/MHz, 100uA standby Crypto engine, Hardware security

Up to 165 DMIPS, 90nm process 500uA/MHz, 2.5 uA standby Ethernet, CAN, USB, Motor Control, TFT Display

High Performance CPU, Low Power

Ultra Low PowerGeneral Purpose

RX

Ethernet, CAN, USB, UART, SPI, IIC


Innovation

DVR

Game Console

Smart Phones Navigation Systems

Music Players

Tablet PC


Our RTOS Solutions

Renesas provides you a complete set of FREE tools and several

MCUs with different peripherals. We work with FreeRTOS and

other partner companies to arm you with a full set of software

solutions so you can build the next Space Shuttle!


Agenda

Definitions

Why RTOS?

Why FreeRTOS?

Lab Exercises

Questions

Feedback Form


Key Takeaways

By the end of this session you will be able to:

Identify the basic RTOS concepts

Find out how RTOS can help you

Recite why FreeRTOS may be good solution for you

Identify what other RTOS vendor we partner with


What is Your RTOS Experience?

I have previously used an RTOS in a commercial product

I am using an RTOS in my current project

I am considering using an RTOS in the near future and

would like to get as much info as possible

I am a “Super-Loop” user and here to burn you down


Some Definitions

REAL-TIME: Computing with a deadline

Hard real-time (Air bag)

Soft real-time (Adaptive volume)

TASK: Self contained code that handles a singular

functionality or semi-independent portion of an application

Process

Thread

SCHEDULER: Implements the scheduling policy

Kernel

Operating system (OS)

PRIORTY: Used in arbitration mechanism


Why Use an RTOS? (1)

Abstracting timing information

Kernel is responsible for system time

Modularity

Tasks are independent modules with well defined purpose

Team development

Designers can work on different tasks simultaneously

Code reuse

Modules allow code re-use with less effort

Improved efficiency

Event driven software

Code executes only when it is needed


Why Use an RTOS? (2)

Flexible interrupt handling

Short interrupt routines that detects events

Most of the work deferred to a task

Mixed processing requirements

Periodic execution

Continuous functions

Event driven processing

Real-time requirement ordering with priorities

Control over peripherals

Shared resources

Gatekeeper tasks


Why FreeRTOS?

Widely used and known

Open source

Free use and distribute

Simple and easy to port

Feature rich but small size

Path to commercial versions

OpenRTOS: Full support, additional components

SafeRTOS: Functional safety, IEC 61508 compliant

More on: http://www.freertos.org/

http://www.freertos.org/


What is our role with FreeRTOS?

Port FreeRTOS to Renesas MCUs

Work with FreeRTOS to qualify ports

Provide sample projects with FreeRTOS

Direct Drive LCD

Integrated Firmware Development Platform

Support by FreeRTOS

Partner with other RTOS vendors for full support

Micrium: uc/OS

Segger: embOS

CMX: CMX-RTX


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Lab Exercises


General Notes on Lab Exercises

Refer to lab handout

Total of 8 lab exercises

Short description up

front

About 10 minutes each

Recap at end

LEDs show running task

LED4 System Tick

LED5 Task1

LED6 Task2

LED7 Task3

LED8 Task 4

LED9 Run time stats

LED10 Idle Task


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Lab Exercise 1 - Tasks, Priorities, Task States


Lab Exercise 1 - Tasks, Priorities, Task States

APIs: xTaskCreate(), vTaskDelay(), vTaskDelayUntil(), vTaskStartScheduler()

Pre-emptive scheduling Highest priority ready task

Time slice same priority tasks

Idle task Low priority background or

continuous tasks

Spare processing time

System in low power

MUST NOT BLOCK!

Suspended

Ready

Blocked

Running

vTaskSuspend()

vTaskSuspend() vTaskResume()

vTaskSuspend()Event

Blocking API function


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Lab Exercise 1 – You can start the lab now


Lab Exercise 1 – Recap

Time

Priority

Task1 Task2

t1 t2 t3 t4

Time

Task1 Task2

t1 t2 tn

Task3

Idle

Priority

2tn

2 tasks with same priority running to completion

3 tasks with different priorities that block


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Lab Exercise 2 – Task Properties


Lab Exercise 2 – Task Properties

APIs: uxTaskPriorityGet(), vTaskPrioritySet(), vTaskDelete(),

vTaskSuspend(), vTaskResume()

Task handle

Used to access to a task

Query properties

Modify properties

Suspend

Resume

Delete


25




Task1 is the highest priority task.

How do Task2 run?

Task1 raises priority of Task2 so it

can run. Task2 lowers its priority.

What does happen when task

priorities not changed?

Task1 becomes the only running

task

Adding a delay allows Task2 to

run. In this case Task2 runs once

because it deletes itself.



Hard real time -> Higher priority

Soft real time -> Lower priority

Execution times

Processor utilization

Rate Monotonic Scheduling (RMS)

Unique priority based on the periodic execution rate

The higher periodic execution the higher the priority

Better scheduling of tasks

Not all tasks are periodic

Execution times must be considered


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Lab Exercise 3 – Queue Management


Lab Exercise 3 – Queue Management

APIs: xQueueCreate(), xQueueSendToBack(), xQueueSendToFront(), xQueueReceive(), uxQueueMessagesWaiting()

Communication between tasks and interrupts

Blocking API call

Not owned by a particular task Any task can write to a queue

Any task can read from a queue

Byte by byte copy of the data

Tail

Head

Tail

Head

20

Send 20

Tail

Head

2010

Send 10

Tail

10

Head

Receive 20


Lab Exercise 3 – More on Queues

Use pointers for large data Pointers queued

Some rules must be followed

Clearly define the owner of RAM Avoid simultaneous memory

modifications

Sending task accesses the memory until pointer is queued

Receiving task accesses the memory after the pointer is received from the queue

NO ACCESS IN BETWEEN!

Make sure RAM being pointed is valid DO NOT USE STACK!

Tail

Head

2010

RAM


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Receiver task is the highest

priority task so it runs as soon as

data is sent to queue and

removes it. Therefore, the items

in queue is always zero.

Receiver task priority is lower

than the sender task. Sender

tasks fills the queue and can not

send anymore.

All tasks are at the same priority

so they are time-sliced.


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Lab Exercise 4 – Interrupt Management


Lab Exercise 4 – Interrupt Management

Events Message reception

Button push

Exceeding a threshold

Detection methods Polled

Interrupt driven

Timing In the ISR

In the handler task

Semaphores links events to tasks

Let’s look at a sequence of events

Time

Task1

t1 t2 t3

ISR

Priority

Handler Task


Lab Exercise 4 – Semaphores

APIs: vSemaphoreCreateBinary(),

xSemaphoreCreateCounting(),

xSemaphoreGiveFromISR(), xSemaphoreTake()

Binary semaphore

Queue with a length of one

Always either empty or full

Counting semaphore

Event count, initial value = zero

Resource management, initial count = number of resource

TaskInterrupt gives the

semaphorexSemaphoreGiveFromISR()

TaskTaskSemaphore is available. Task

unblocks.

Another interrupt event gives the semaphore

xSemaphoreGiveFromISR()xSemaphoreTake()

Task


36




Binary semaphores are available after created.

Sequence of events: Periodic task causes an interrupt ISR runs and gives the semaphore ISR pends a context switch Context switches and handler

task runs Context switches back to periodic

task

Same sequence of events with counting semaphore but multiple events are captured.


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Lab Exercise 5 – Queues and Interrupts


Lab Exercise 5 – Queues and Interrupts

APIs: xQueueReceiveFromISR(),

xQueueSendToBackFromISR(),

xQueueSendToFrontFromISR()

FromISR() APIs

Do not specify block time therefore they do not block

Do not perform context switch

Indicate if a higher priority task moves to ready state

A port specific macro causes immediate context switch

If the macro is not called in ISR:

– context switch happens at the next timer tick


40




Generator task sends 5 integer values to integer queue and causes an interrupt

ISR receives the integers, uses them to select strings and sends them to string queue

String tasks receives the strings and prints them out

If context switch is not scheduled within ISR, generator task runs to completion before string task runs



xQueueSendToFrontFromISR() API

Back / Front same as FIFO / LIFO

Notice the difference in the sequence of strings

SendToBack SendToFront


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Lab Exercise 6 – Resource Management


Lab Exercise 6 – Resource Management

Resource sharing/Peripheral access

LCD, standard IO, memory

Read/Modify/Write operation

Non-atomic operations

Non-atomic access to variables

Multiple member of a structure

32-bit access on a 16-bit device

Reentrant Functions

Safe to call from more than one task/interrupt

No data access other than on the stack or registers


Lab Exercise 6 – Best Practices

Do not share resources

Use mutual exclusion when accessing a shared

resource

Access a resource only from a single task

RTOS tools for resource management

Creating critical sections

– taskENTER_CRITICAL()

Suspending the scheduler

– vTaskSuspendAll()

Make use of mutexes

Designing gatekeeper tasks


Lab Exercise 6 – Mutual Exclusion = Mutexes

APIs: xSemaphoreCreateMutex(), xSemaphoreTake(),

xSemaphoreGive()

Special type of binary semaphore

Used to control a shared resource

A task “takes” the mutex before accessing the resource

No other tasks can use the resource when mutex is taken

The task “gives” the mutex back after it is done

Resource is now available to other tasks

Works as longs as all agree with these rules

DO NOT COME IN FROM THE BACK DOOR!


47




Print 2 is a higher priority

tasks and preempts Print 1

task corrupting the output

Why we did not see this in

previous exercises?

No corruption in the output

when mutex is used


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Lab Exercise 7 – Priority Inversion, Inheritance


Lab Exercise 7 – Priority Inversion, Inheritance

Time

LP Task

t1 t2 t3

HP Task

MP Task

t5 t6

Priority Inversion: HP task delayed by LP and MP tasks

Time

LP Task

t1 t2 t3

HP Task

MP Task

t5t4

Priority Inheritance: LP task raises its priority to HP task priority


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Initially, LP task takes the

resource, and resumes MP task

MP task takes 8 seconds to

complete

HP task attempts to run every 1

second but it blocks waiting for

the resource

LP task’s priority raises to HP

task level and gives the resource

back with no delay

HP task runs every 1 second

8 seconds delay

HP task runs about 8

times between LP

task executions

No delay


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Lab Exercise 8 – Gatekeeper Tasks


Lab Exercise 8 – Gatekeeper Tasks

Gatekeeper tasks has sole ownership of a resource

Only the gatekeeper tasks accesses the resource

Other tasks access the recourse through the services

provided by the gatekeeper

Things to consider when creating gatekeeper tasks

Up front system design

Agree on services and interfaces

Allow for future expansion/changes

Always use the services to access the resource


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Print 1, Print 2 tasks and an interrupt service routine

use the services of a gatekeeper task

Gatekeeper task uses a queue as an interface

No corruption with the print out


Innovation

Renesas is here to help you to create your next

innovation. Let’s build it together!


Questions?


59

Thank You!

Renesas Electronics America Inc.

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