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Tornado and VxWorks
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Tornado-VxWorks ArchitectureTornado-VxWorks ArchitectureThe Real-Time, Multitasking OSIntertask Synchronization and CommunicationThe Project FacilityThe Debugging ToolsThe Networking Stack
Tornado and VxWorks
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What is Tornado?
Real-Time,
Multitasking
OS
Development and Debugging
Tools
Networking
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Tornado Architecture - HW Target
The tools, registry, and target server can run on different hosts
VxWorks
Target Agent
Tool
Tool
Tool
Host Target
Target
Server
Registry
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Tornado Architecture - Simulator Target
VxWorks runs as a process under the host OS The simulator architecture provides no emulation of
instruction, native compilers are used
Registry
Target
Server
VxWorks
Target Agent
Tool
Host
Tool
Tool
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Tornado ArchitectureThe Real-Time, Multitasking OSThe Real-Time, Multitasking OSIntertask Synchronization and CommunicationThe Project FacilityThe Debugging ToolsThe Networking Stack
Tornado and VxWorks
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What is a Task?
A task is a• Kernel object dynamically created at runtime• Logical entity consisting of a Task Control Block (TCB) data structure and
stack space• An independent thread of execution
A task is not a function • However, a special purpose function (typically designed with an endless
loop) is used for the task’s entry point
• Functions execute within the context of tasks • The VxWorks routine taskSpawn() invokes the entry point function foo
and gives the task it’s thread of “liveness”
foo(){
for (;;){waitForData( );/* Until external event occurs */processData( );}
}
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Creating a Task
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Multitasking
Separate tasks are created to perform different system requirements• For example, data acquisition and data computation
Each task alternates between “ready” and “waiting” • A “task manager” (the multitasking kernel) is therefore required
VxWorks allows a task to wait for• A specified time delay (Delay)
• An event such as an interrupt (Pend)
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Task States
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Multitasking Kernel
The “wind” kernel is that part of VxWorks which directly manages tasks
It allocates the CPU to tasks according to the VxWorks scheduling algorithm
It uses Task Control Blocks (TCBs) to keep track of tasks• One per task
• Declared as WIND_TCB data structure in taskLib.h
• O.S. control information
– state, task priority, delay timer,breakpoint list, error status,I/O redirections
• CPU Context Information
– PC, SP, CPU registers, FPU registers
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Kernel Operation
Scheduler
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Multitasking Facilities
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Tornado-VxWorks ArchitectureThe Real-Time, Multitasking OSIntertask Synchronization and CommunicationIntertask Synchronization and CommunicationThe Project FacilityThe Debugging ToolsThe Networking Stack
Tornado and VxWorks
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Intertask synchronization
In a multitasking environment, facilities to achieve mutual synchronization are needed• Producer-consumer architecture
• Client-server architecture In VxWorks, intertask synchronization is achieved using
• Binary Semaphores
• Message Queues
• Events
• Pipes Some intertask synchronization facilities (queues and
pipes) also enable data transmission (intertask communication)
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Binary Semaphores
Binary semaphores exist in one of two states• Full (synchronizing event has occurred)
• Empty (synchronizing event has not occurred)
Intertask synchronization is obtained by creating an empty, binary semaphore for the synchronizing event• The task waiting for the event calls semTake( ) and blocks until
the semaphore is given
• The task or interrupt service routine detecting the event calls semGive( ), which unblocks the waiting task
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Message Queues
Message queues are kernel objects used for passing information between tasks
Message queues provide a FIFO buffer of messages
The task waiting for the synchronization message calls msgQueueReceive( ) and blocks until a message is on the queue
The task sending the synchronization message calls msgQueueSend( ), which unblocks a pending task
Task A Task B
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Pipes
Pipes provide an alternative interface to the message queue facility in the VxWorks I/O system
Tasks block • When they read from an empty pipe, until data is available
• When they write to a full pipe, until there is space available Similar to their use of message queues, interrupt service
routines can write to a pipe, but cannot read from it
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Events
VxWorks events are means of synchronization between• Tasks and tasks• Interrupt service routines and tasks• VxWorks objects (binary semaphores and message queues) and
tasks Only tasks can receive events, whereas tasks, interrupt
service routines or VxWorks objects can send events Events are synchronous in nature
• The receiving task pends while waiting for the events to be sent Events allow a task to wait simultaneously on multiple
resources• For example, events can be sent by semaphores, message
queues and other tasks
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Mutual Exclusion Semaphores
Mutually exclusive access to shared resources is provided in VxWorks by mutual-exclusion semaphores (mutexes)
VxWorks mutexes are designed to address issues inherent to mutual exclusion, like• Priority inversion• Deletion safety• Recursive access to the shared resource• Semaphore ownership
Each critical section of the code has to be protected with mutexes, by having a task• Take the mutex before accessing the code• Give the mutex after having accessed it
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Counting Semaphores
Counting semaphores are similar to binary semaphores, except that they keep track of the number of times the semaphore is given or taken• Every time the semaphore is given, the count is incremented
• Every time the semaphore is taken, the count is decremented
• When the count reaches zero, a task that tries to take the semaphore is blocked
Counting semaphores are useful for guarding multiple copies of resources
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Signals
Signals asynchronously alter the control flow of a task• An interrupt service routine or a task can send a signal to a task
• The task which has received the signal will asynchronously execute a signal handler
• The signal handler executes in the receiving task’s context and makes use of the task’s stack
• If no signal handler is installed, the received signal is ignored
Since signals are asynchronous in nature, they are more appropriate for error and exception handling than as a general-purpose intertask communication mechanism
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Tornado-VxWorks ArchitectureThe Real-Time, Multitasking OSIntertask Synchronization and CommunicationThe Project FacilityThe Project FacilityThe Debugging ToolsThe Networking Stack
Tornado and VxWorks
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Projects
The project facility allows one to manage two project types• Bootable projects
– To configure and build a VxWorks image
• Downloadable projects
– To build and download application modules to a running target
Projects can be grouped together in Workspaces For each project more than one build specification can be
used
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Bootable projects
Bootable projects are used to create a new, customized VxWorks image• The system image consists of all desired system modules linked
together in a single, non-relocatable object module with no unresolved external references
• The image can be customized by adding or removing VxWorks components from the Workspace GUI
A bootable project is created specifying• A BSP
• A toolchain (GNU or Diab)
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Downloadable Projects
Downloadable projects are used to create relocatable object modules that can be downloaded and dynamically linked to VxWorks• Module downloading and dynamic linking is performed by the
Target Server, which maintains a host-resident target’s symbol table
Downloadable projects • Are created by specifying a toolchain
– GNU or Diab
• Allow “on the fly” development
– Modules can iteratively be downloaded, tested and debugged without rebooting the target system
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Project Facility Workspace Window 3 Workspace window views
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Tornado-VxWorks ArchitectureThe Real-Time, Multitasking OSIntertask Synchronization and CommunicationThe Project FacilityThe Debugging ToolsThe Debugging ToolsThe Networking Stack
Tornado and VxWorks
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Host-Resident Debugging Tools
WindShell Command Shell• Provides command-line based, interactive access to all run-time
facilities Browser
• System-object viewer, graphical companion to WindShell CrossWind Debugger
• Remote source-level debugger
• Extended version of the GNU source-level debugger (GDB) WindView Software Logical Analyzer
• Dynamic visualization tool
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WindShell
WindShell allows one to • Access all VxWorks facilities by allowing calls to any VxWorks
routines
– For example,
› Spawning tasks
› Creating VxWorks objects like semaphores, message queues, and pipes
• Download object modules to the target system
• Perform assembly-level debugging
• Create and examine variables symbolically
• Examine and modify memory
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WindShell
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Browser
The browser monitors the state of a target It shows detailed information on
• Tasks • VxWorks objects (semaphores, message queues, ...)• Stack usage by all task on the target• Target CPU usage by task• Object-module structure and symbols• Interrupt vectors
The displays are snapshots, which can be updated interactively• Alternatively, the Browser can be configured to automatically
update its display at specified intervals
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Browser
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CrossWind
CrossWind is a source level, graphical, debugging front-end using an enhanced version of GDB as its debugging engine
It allows two debugging strategies• Task mode debugging
– One task runs under debug control, while other tasks are not affected
– CrossWind can either› Attach to a running task, or› Start a new task under debugger control
• System mode debugging– Whenever a task hits a breakpoint, the whole system stops– This is useful to debug tasks, interrupt service routines and
pre-kernel execution
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CrossWind
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WindView 2.2
WindView allows one to study dynamic interactions of all the elements of complex, real-time systems
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WindView 2.2
The WindView graph provides manageable access to important application information
WindView allows• Scrolling the information forward and backward in time
• Zooming in/out
• Tailoring the display to only focus on the tasks and events of interest
• Setting locks on certain events and searching for their successive occurrences
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WindView 2.2 Example
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Problem Solving with WindView 2.2
WindView allows to• Detect race conditions, deadlocks, CPU starvation and other
problems related to task interaction
• Determine application responsiveness and performance
• See cyclic patterns in application behavior
• Conduct post-mortem analysis of failed systems
• Detect memory leaks
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Tornado-VxWorks ArchitectureThe Real-Time, Multitasking OSIntertask Synchronization and CommunicationThe Project FacilityThe Debugging ToolsThe Networking StackThe Networking Stack
Tornado and VxWorks
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VxWorks Network Components
IP
TCP UDP
Socketszbuf
Shared MemoryNetwork
PPPEthernet
MUX
ftp rsh telnet
Target server NFS
rlogin
netDrv
RPC
Application layer
Application programminginterface
Transport layer
Network layer
Link layer
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Shared-Memory Backplane Network
This allows multiple processors to communicate over their common backplane as if they were communicating over a network by using a standard network driver
host
vx3
Ethernet
Shared-MemoryNetwork
Backplane (e.g. VME, PCI)
vx2 vx1
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MUX – The Network Driver Interface
This interface decouples the link layer and the network layer• The network protocol does not need to be modified when adding
new network dirvers
• A new network protocol can be added without modifying the existing MUX-based network driver interfaces
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TCP/IP Protocol Suite
Based on the 4.4 BSD TCP/IP release, the TCP/IP protocol suite comprises• UDP – User Datagram Protocol
– Low-overhead delivery mechanism of datagrams, used by several applications like BOOTP, DHCP, DNS, TFTP, ...
• TCP – Transmission Control Protocol– Reliable, end-to-end transmission mechanism, used by Telnet,
Rlogin, FTP, ...• IP – Internet Protocol
– Hop-by-hop protocol to transmit datagrams• ICMP – Internet Control Messagge Protocol
– Reports unexpected events in data transfer, used by ping• IGMP – Internet Group Management Protocol
– Used to support multicasting
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Sockets
Sockets allow processes to communicate within a single CPU, across an Ethernet, across a backplane or across any connected combination of networks
VxWorks provides• BSD Sockets
– Datagram Sockets (UDP)
– Stream Sockets (TCP)
– Raw Sockets
• Zbuf Sockets
– An alternative set of sockets based on a data abstraction called zbuf, zero-copy buffer
– Applications can read and write BSD sockets without copying data between application buffers and network buffers
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Remote Access Applications
RSH – Remote Command Execution• Allows a VxWorks application to run commands on a remote
system and receive the command results on standard output and error over socket connection– Only the client side implementation is provided– A server running on the remote system is assumed
FTP – File Transfer Protocol• Both client and server applications are provided
NFS – Network File System• Server component
– A target running VxWorks act as a file server for any system that runs an NFS client
• Client component– A target running VxWorks can mount a remote file system
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Remote Access Applications (cont’d)
TFTP – Trivial File Transfer Protocol• Client and Server applications are provided• Unlike FTP or RSH, TFTP does not require any authentication
Rlogin – Remote Login• On a VxWorks terminal, rlogin( ) gives users the ability to log in to
remote systems on the network• The remote login daemon, rlogind( ), allows remote users to log
in to VxWorks Telnet
• The server application only is provided RPC – Remote procedure call
• RPC implements a client-server model of task interaction• A client requests a remote service from a server and waits for a
reply
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DNS and SNTP
DNS – Domain Name System• DNS is a distributed database used by TCP/IP applications that
maps hostnames to IP addresses
SNTP – Simple Network Time Protocol • Client and server components are provided
– The client is normally used to maintain its system internal clock accuracy based on time values reported by one or more servers
– The server provides time information to other systems
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BOOTP – Bootstrap Protocol
The BOOTP server• Retrieves boot information from the Bootp Database (bootptab)
• Supplies an Internet host with an IP address and related configuration information
– The IP address is permanently assigned The BOOTP client
• Uses broadcasts to discover an appropriate server
• Lets a target retrieve a set of boot parameters like an IP address and a filename of the bootable image
Both client and server components are provided BOOTP is implemented on top of UDP
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DHCP – Dynamic Host Configuration Protocol Like BOOTP, DHCP allows the permanent allocation of
configuration parameters to specific clients However, DHCP also supports the assignment of a
network address for a finite lease period VxWorks includes a DHCP client, server, and relay agent The client can retrieve one or more sets of configuration
parameters from either a DHCP or BOOTP server The server can process both BOOTP and DHCP
messages The DHCP relay agent provides forwarding of DHCP and
BOOTP messages across subnet boundaries
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IP Routing
If the destination is directly connected to the sender (e.g., a point-to-point link) or on a shared network (e.g., Ethernet), then IP datagrams are sent directly to the destination • Otherwise, the sender sends the IP datagrams to a default router,
and lets the router deliver them to destination Each router maintains a routing table, which is used to
deliver the IP datagrams to either • A local IP address, for a direct route, or
• The next-hop router IP address, for an indirect route
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Dynamic Routing Protocols
Dynamic routing occurs when routers talk to adjacent routers, informing each other of what network each router is connected to
Entries in the routing tables change dynamically as routes change over time
The Routing Information Protocol (RIP) is provided with VxWorks• This is intended for small to medium-sized networks
– The longest path must be less than 16 hops
• It uses a distance-vector protocol
– It contains a vector of distances as the hop count
• RIP version 1 and 2 are supported
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Summary
Tornado’s three components• VxWorks, real-time, multitasking operating system
– Priority-based, preemptive scheduling algorithm
– Intertask synchronization and communication services
• Project facility and debugging tools
– Bootable and downloadable projects
• Networking
– Connects hosts and targets during development and debugging
– TCP/IP stack
– Rich set of network applications and protocols
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References
Manuals available either in the Tornado on-line help, or via the Wind River Bookstore at: www.windriver.com/windsurf/bookstore• Tornado User’s Guide
• WindView User’s Guide and User’s Reference
• VxWorks Programmer’s Guide
• VxWorks OS Libraries
• VxWorks Network Programmer’s Guide