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VxWorks设备驱动编写方法是嵌入式系统开发中的一个重要环节，它涉及到操作系统与硬件之间的交互，使得应用程序能够高效地访问和控制硬件资源。VxWorks是由Wind River Systems开发的一款实时操作系统（RTOS），广泛应用于航空航天、工业自动化、通信等领域。在VxWorks中，设备驱动程序扮演着连接硬件和上层软件的桥梁角色。 1. **驱动分类**： - 基本驱动：直接操作硬件，如中断处理和寄存器读写。 - 高级驱动：基于基本驱动构建，提供更高级别的功能，如缓冲区管理和多线程支持。 - 总线驱动：处理总线上的设备，如PCI、USB等。 - 类驱动：基于设备类，如网络驱动、块设备驱动等。 2. **驱动模型**： VxWorks采用模块化、层次化的驱动模型，包括设备驱动接口（DDI）、设备驱动服务（DDK）和设备驱动程序三部分。DDI是操作系统提供的标准接口，DDK是开发驱动程序所需的库和工具，而驱动程序则实现具体硬件的功能。 3. **驱动结构**： - 启动/初始化：设置硬件状态，分配资源。 - 打开/关闭：控制设备的使用和释放。 - 读/写：数据传输操作。 - 中断处理：响应硬件中断，执行相应操作。 - 错误处理：处理设备错误。 4. **中断处理**： VxWorks支持中断级处理，中断服务例程（ISR）需快速完成任务并恢复上下文。通常，ISR仅进行必要的硬件操作，复杂任务交由中断服务任务（IST）处理。 5. **内存管理**：驱动程序需要合理管理内存，如使用VxWorks的动态内存分配函数malloc()和free()，以及静态内存池。 6. **同步机制**：为了确保并发访问的安全，驱动程序通常会使用信号量、互斥量等同步原语。 7. **调试技巧**：使用VxWorks内置的调试工具如WindView、TaskView，以及标准的GDB调试器进行驱动调试。 8. **驱动注册**：完成驱动程序编写后，需要将其注册到VxWorks的设备驱动管理器中，以便操作系统能够找到并使用它。 9. **配置文件**： VxWorks的配置文件（config.h）用于定义系统中包含的设备驱动，驱动的初始化信息等。 10. **示例分析**：例如，一个串口驱动可能需要实现初始化串口、设置波特率、打开/关闭串口、读写数据等功能。通过分析`VxWorks-device-drivers.doc`文档，可以深入理解这些概念和步骤。编写VxWorks设备驱动涉及多个层面的知识，包括硬件接口、中断处理、内存管理、同步机制等。开发者需要对VxWorks内核有深入理解，并熟悉相关硬件原理。通过阅读和研究提供的文档，可以逐步掌握这一过程，并有效地开发出满足需求的驱动程序。

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VxWorks-device-drivers.doc 324KB

VxWorks - Device drivers in a nut shell

Prasad Ayyalasomayajula

Allen Tully

reserved by AyyalaSoft. payyalas@ayyalasoft.com, payyalas@yahoo.com

# See file CREDITS for list of people who contributed to this

# project.

# This program is free software; you can redistribute it and/or

# modify it under the terms of the GNU General Public License as

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# the License, or (at your option) any later version.

# This program is distributed in the hope that it will be useful,

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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

# GNU General Public License for more details.

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# along with this program; if not, write to the Free Software

# Foundation, Inc., 59 Temple Place, Suite 330, Boston,

# MA 02111-1307 USA

Legal Stuff: You are at your own risk on using the contents of this material.

AyyalaSoft is not responsible in any way for your assumptions, mistakes based

on the contents of this material.

Table Of Contents

Preface

Chapter 1: REAL-TIME SYTEMS AND VXWORKS

Chapter 2: Tour of VxWorks

Chapter 3: Interrupts and Interrupt handling

Chapter 4: Devices and Drivers

Chapter 5: Character Drivers

Chapter 6: Block Drivers

Chapter 7: Real World Scenarios

Chapter 8: User Interaction with a driver

Chapter 9: Advanced Topics

Preface

This book if for device driver developers, who have general back ground in real time

operating systems. This book addresses device driver development using

VxWorks/Tornado 5.4.

Acknowledgements

We referred to VxWorks 5.4 programmers manual and other websites to make sure

that the content is as accurate as possible. We hope you enjoy this work, and drop an

email to me at payyalas@yahoo.com for suggested improvements. Very soon we will

add few more code samples to my website www.ayyalasoft.com.

Regards

Prasad Ayyalasomayajula

Allen Tully

1) REAL-TIME SYTEMS AND VXWORKS:

Operating systems can be categorized into real-time and non-real-time systems. A

real-time system is defined as a system where the response time for an event is

predictable and deterministic with minimal latency. The architecture of the operating

system's scheduler, also referred to as the dispatcher, has a significant impact on the

responsiveness of the OS. Preemptive scheduling ensures the highest priority

task/thread always runs and doesn’t relinquish the CPU until its work is done or a

higher priority task becomes available. A preemptive scheduler also implies a real-

time kernel. Several aspects to consider when selecting a real-time OS are:

 Foot print of the kernel

 Interrupt latency

 Interrupt response time

 Interrupt recovery

 Multi-tasking

 Task context switching

 Virtual memory support etc.,

VxWorks provides a real-time kernel that interleaves the execution of multiple tasks

employing a scheduling algorithm. Thus the user sees multiple tasks executing

simultaneously. VxWorks uses a single common address space for all tasks thus

avoiding virtual-to-physical memory mapping. Complete virtual memory support is

available with the optional vxMem library.

2) Tour of VxWorks

Tasks

A task is an independent program with its own thread of execution and execution

context. Every task contains a structure called the task control block that is

responsible for managing the task's context. A task’s context includes

 program counter or thread of execution

 CPU registers

 Stack of dynamic variables and function calls

 Signal handlers

 IO assignments

 Kernel control structures etc.,

Every task has a name and an ID associated with it. Each task is assigned a default

priority as well. A task has four states as shown below.

A task can be created with taskInit() and then activated with taskActivate() routine or

both these actions can be performed in a single step using taskSpawn(). Once a task is

created it is set to the suspend state and suspended until it is activated, after which it

is added to the ready queue to be picked up by the scheduler and run. A task may be

suspended by either the debugging your task, or the occurrence an exception. The

difference between the pend and suspend states is that a task pends when it is waiting

for a resource. A task that is put to sleep is added to delay queue.

Scheduler

VxWorks scheduler determines which task to own the CPU time. By default, the

scheduler runs a preemptive algorithm. Preemptive scheduler guarantees that the

highest priority task preempts a lower priority task. There are some special cases

called priority inversion which is discussed in advanced concepts.

The scheduler can be set to run round robin algorithm which is a time slicing

algorithm.

Mutual Exclusion

Mutual exclusion can be implemented in VxWorks in the following three ways.

 Semaphores

 Disabling Interrupts

 Disabling the scheduler using taskLock()

Semaphores

VxWorks supports three types of semaphores, binary, mutual exclusion, and

counting, each of which is optimized for a specific application. Semaphores are

generally used for task synchronization and communication, and protection of shared

resources also referred to as concurrency control or mutual exclusion.

 Binary semaphores are the fastest and are best suited for basic task

synchronization and communication.

 Mutual exclusion semaphores are sophisticated binary semaphores that are

designed to address the issues relating to task priority inversion and semaphore

deletion in a multitasking environment.

 Counting semaphores maintain a count of the number of times a resource is

given. This is useful when an action is required for each event occurrence. For

example if you have ten buffers, and multiple tasks can grab and release the

buffers, then you want to limit the access to this buffer pool using a counting

semaphore.

Message Queues

VxWorks supports messages queues for inter task communication. A variable number

of messages, each of variable length, can be sent to any task. ISRs and tasks can send

messages but only tasks can receive messages.

Multiple tasks can wait on a single message queue and can be ordered by their

priority. Messages can be marked urgent for faster delivery.

Network Intertask Communication

VxWorks supports general facilities like pipes, sockets, RPC and signals for network

inter task communications.

Additional Facilities

VxWorks provides facilities like Asynchronous IO and buffered IO for application

and driver development. It is also POSIX library.

3) Interrupts and Interrupt handling

Interrupt is the mechanism by which a device seeks the attention of CPU. The piece

of user code that the CPU executes on interrupt is called interrupt service routine

(ISR). The Kernel doesn’t transfer execution to the ISR immediately. It does some

house keeping before the ISR is executed. The delay between the occurrence of

interrupt and time spent by the kernel before it executes the first ISR instruction is

called Interrupt response time. This equals the sum of interrupt latency and time to

save CPU’s context and execution time of kernel ISR entry function.

VxWorks provides a special context for interrupt service code to avoid task

context switching, and thus renders fast response. VxWorks supplies interrupt

routines which connect to C functions and pass arguments to the functions to be

executed at interrupt level. To return from an interrupt, the connected function

simply returns. A routine connected to an interrupt in this way is referred to as an

interrupt service routine (ISR) or interrupt handler. When an interrupt occurs, the

registers are saved, a stack for the arguments to be passed is set up, then the C

function is called. On return from the ISR, stack and registers are restored.

IntConnect(INUM_TO_IVEC(intNum), intHandler, argToHandler) allows

C functions to be connected to any interrupt. The first argument to this routine is the

byte offset of the interrupt vector to connect to. The second argument is the interrupt

handler and the last is any argument to this handler.

One can disable interrupts using intLock() for synchronization. Care should be

taken to re-enable the interrupts using intUnlock(). If you are planning for nested

interrupts, you should not disable interrupts using intLock(). Also make sure that your

code is reentrant and you allocate enough stack resources for nesting.

áPoints to remember

a) Within an ISR, limited capabilities exist for the user code. Not all library

functions are available.

b) Since memory facilities malloc() and free() take semaphores, they cannot be

called within ISR.

a) Any blocking call is to be avoided.

b) Semaphores can be given, but not taken from an ISR.

áPoints to remember

ISR can communicate with user tasks via

a) shared memory and ring buffers

b) release of semaphores

c) signal tasks

d) writing to pipes

e) sending messages using message queue

Understanding ISR and what goes on within interrupt handler is the key to designing

your driver. Many real world drivers just have an interrupt handler and interact with

user and device without the rest of the interfaces. Please refer to 7) for examples.

4) Devices and Drivers

A driver supplies a uniform device independent logical interface to the user to interact

with a device. A device can be a piece of hardware such as your hard drive or can be

a piece of software such as a pipe or a socket, but a driver is always a software

module. A driver can control multiple devices. If the architecture allows virtual

memory, driver works in a logical/virtual address space, but a device works in a

physical address space.

timercrack

2012-01-11

这是从人家官网直接复制的资料。

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