Embed Size (px)
DESCRIPTION
Decisions Behind the Design: LabVIEW for CompactRIO Sample Projects. Meghan Kerry Embedded Software Product Manager Certified LabVIEW Developer (CLD). Agenda. Keys to quality in a software architecture Software architecture overview I/O safe states Watchdog timers Message communication - PowerPoint PPT Presentation
Citation preview
1ni.com
ni.com
Decisions Behind the Design: LabVIEW for CompactRIO
Sample ProjectsMeghan Kerry
Embedded Software Product ManagerCertified LabVIEW Developer (CLD)
3ni.com
Agenda
• Keys to quality in a software architecture• Software architecture overview• I/O safe states• Watchdog timers• Message communication• Error handling • System monitoring
4ni.com
Keys to Quality in a Software Architecture
• Define software architecture and identify architecture components
• Create an architectural diagram• Consider key components such as data communication, error handling, etc.
• Learn the foundational design patterns• Create new design patterns as required by your application (requires experience)
5ni.com
Data Communication Diagram
• Documents foundational components:• Processes (loops)• Data communication paths• Type of data transfer
6ni.com
Data Communication Types
Tag Latest value data
Messages/Commands Intermittent data, low latency
Stream Continuous acquisition, high throughput
7ni.com
Typical CompactRIO System Diagram
8ni.com
LabVIEW for CompactRIO Sample Projects• Pre-built architectures for embedded control and monitoring applications
• Designed to ensure quality and scalability of a system
9ni.com
Basic FPGA Diagram
Performs deterministic and/or high speed control
10
ni.com
State Machine for Hardware I/O and Control
11
ni.com
Failure Conditions that Initiate Safe States
• Examples (from Fail Safe Reference Design):
• RT Safe – indicates the RT system is ready
• Emergency Safe – tied to an emergency shut-off switch
• Watchdog Safe – monitors the Real-Time system
• Control Inputs Valid – monitors the inputs to the control algorithm
• Based on system requirements
12
ni.com
Basic FPGA Diagram
Detects software failures
Recovers from software failures
13
ni.com
Watchdogs
• A watchdog timer is a hardware counter that interfaces with the embedded software application to detect and recover from software failures
• A user can then:• Reboot real-time target automatically• Perform user-defined recovery actions
• Two types of watchdogs with NI Real-Time hardware:
• LabVIEW Real-Time Watchdog • Real-Time <-> FPGA Watchdog (FPGA Fail Safe Design)
14
ni.com
LabVIEW Real-Time Only Watchdog
• Uses hardware timer built into CompactRIO hardware
• “Reset = True” reboots system if the watchdog process is starved
15
ni.com
LabVIEW Real-Time Watchdog
• Enable occurrence in expiration actions• Configure appropriate watchdog timeout and Watchdog Whack loop period
16
ni.com
Real-Time <-> FPGA WatchdogReset timer
Put control loop into a safe state, and reset system
17
ni.com
Real-Time <-> FPGA Watchdog
• Pet the watchdog at a user-defined watchdog pet rate
• This resets the counter implemented in the FPGA VI
See Fail-Safe Control Reference Design whitepaper
18
ni.com
Basic FPGA Diagram - Summary
Detects software failures
Recovers from software failures
Performs deterministic and/or high speed control
19
ni.com
Basic Real-Time Processor Diagram
Periodically communicates
tags
Communicates messages with
clientSends messages to other processes or
targets
20
ni.com
Constructing a Message
Examples
DataVariant allows data-type to vary. Different messages may require different data
CommandString constant allows user to specify message
Command Data
Update Control Configuration
Cluster containing configuration data
Update FPGA State Enum
Update PID Setpoints Array of numerics
Send Error to UI Error cluster
Exit -
21
ni.com
Queued Message Handler API
22
ni.com
Queued Message Handler Framework
Message handling loop
Watchdog Loop
Monitoring Loop
Command ParserQueued Message Handler Setup
23
ni.com
Queued Message Handler Framework
Watchdog Loop
Monitoring Loop
Command ParserOne or more messages handled per case
Communicate messages between processes or targets
24
ni.com
Basic Real-Time Processor Diagram
Handles all error messages from
FPGA and RT target
25
ni.com
Error Messages
• Specific Error Handling• Code called in specific
locations to respond with an action to specific error codes
• Possible actions are retry, ignore, correct
• Central Error Handling• High-level code that checks
for errors in an entire system• Responds to classes of errors
rather than specific codes• Uses the classification to
determine which actions to take
QueueCentral Handler
26
ni.com
Central Error Handling Framework
UI message handling loop
Watchdog Loop
Monitoring Loop
Command Receiver Loop
Specific Handler
Specific Handler
Specific Handler
27
ni.com
Central Error Handling Framework
Watchdog Loop
Monitoring Loop
Command Receiver Loop
Specific Handler
Specific Handler
Specific Handler
28
ni.com
Central Error Handling Framework
Get next error based on priority
Return classification of error
Handle classified errors (update FPGA state and/or reboot system)
Log and send all errors to UI
30
ni.com
Basic Real-Time Processor Diagram
Communicates messages with
client
31
ni.com
Sending Commands Across the Network
• Network Streams are great for commands because are they are lossless
• Tips:• Use Flush with zero timeout to minimize latency• Add code to handle UI disconnections (see Sample
Project)
33
ni.com
System Monitoring
Disk Space RAM CPU Bandwidth
EFF
EC
T
Lost Data Crash Starvation
Embedded processors have limited….
34
ni.com
System Monitoring
Current value data can be sent to UI with Shared Variables
Monitor CPU usage per coreExecute loop
periodically
35
ni.com
Network Published Shared Variables
• When to use the Static API:• Small number of variables (less than a dozen)
• When to use the Programmatic API:• Iterate through a large number of variables• Dynamically change the IP address of the cRIO from the
client (client side only)
36
ni.com
Basic Real-Time Processor Diagram
Periodically communicates
tags
Communicates messages with
clientSends messages to other processes or
targets
37
ni.com
Basic HMI Diagram
Generates UI Events using the Event Structure
Processes UI Events and communicates messages with real-time system
Periodically updates UI
38
ni.com
Common Variant Architectures
• Other LabVIEW for CompactRIO Sample Projects• LabVIEW FPGA Control • LabVIEW FPGA Control with Real-Time Sequencer Engine • LabVIEW Real-Time Control (RIO Scan Interface) • LabVIEW FPGA Waveform Acquisition and Logging• LabVIEW Data Logging and Supervisory Control
39
ni.com
FPGA Control with Sequencer Sample Project
40
ni.com
Real-Time Control Sample Project
41
ni.com
FPGA Waveform Acquisition and Logging
42
ni.com
Demo – LabVIEW FPGA Control Sample Project
43
ni.com
LabVIEW for CompactRIO Sample Projects• Available in LabVIEW 2012 and later• Find more best practices at ni.com/compactriodevguide
