Arm Community
Site
Search
User
Site
Search
User
Groups
Arm Research
DesignStart
Education Hub
Graphics and Gaming
High Performance Computing
Innovation
Multimedia
Open Source Software and Platforms
Physical
Processors
Security
System
Software Tools
TrustZone for Armv8-M
中文社区
Blog
Announcements
Artificial Intelligence
Automotive
Healthcare
HPC
Infrastructure
Innovation
Internet of Things
Machine Learning
Mobile
Smart Homes
Wearables
Forums
All developer forums
IP Product forums
Tool & Software forums
Pelion IoT Platform
Support
Open a support case
Documentation
Downloads
Training
Arm Approved program
Arm Design Reviews
Community Help
More
Cancel
Developer Community
Tools and Software
Software Tools
Jump...
Cancel
Software Tools
Arm Development Studio forum
Cortex A9 WFE instruction not working as expected
Tools, Software and IDEs blog
Forums
Videos & Files
Help
Jump...
Cancel
New
Replies
6 replies
Subscribers
127 subscribers
Views
2631 views
Users
0 members are here
Related
Cortex A9 WFE instruction not working as expected
Offline
Rich Podraza
over 7 years ago
Note: This was originally posted on 10th October 2012 at http://forums.arm.com
I'm trying to do a simple test with WFE instruction and EVENTI/O signals. I'm trying to have one A9 enter a wait state with WFE, and have another A9 do some dummy operations while the first is waiting, then do SEV instruction to signal from its SIGNALO to the other A9's SIGNALI. I can verify with my simulation envronment that this signal fires. However, the first A9 is not waiting, it breezes right by the WFE instruction. No assembler warning indicating these instructions aren't supported.
My best clue is in the assembler guide there is the line "If the Event Register is set, WFE clears it and returns immediately," it sounds like this might be happening, but I can't find any reference to "Event Register" in the Cortex A9 TRM, so I'm not sure if this is active by default in my system or what.
Any ideas? Thanks!
Parents
Offline
Martin Weidmann
over 7 years ago
Note: This was originally posted on 11th October 2012 at
http://forums.arm.com
I think you've already spotted the problem - the event register. You don't know its initial state. If it is set, the the core will appear to "wake" immediately.
WFE/SEV are not themselves suitable for implementing synchronization primitives. That is what LDREX/STREX are for.
What I'd suggest in your case is to use a separate flag to indicate the second core has finished. The first core loops waiting for the flag to be cleared - with a WFE in the loop. That way if you wake unexpectedly you can see that the second core hasn;t finished yet and then go back to sleep.
Cancel
Up
0
Down
Reply
Cancel
Reply
Offline
Martin Weidmann
over 7 years ago
Note: This was originally posted on 11th October 2012 at
http://forums.arm.com
I think you've already spotted the problem - the event register. You don't know its initial state. If it is set, the the core will appear to "wake" immediately.
WFE/SEV are not themselves suitable for implementing synchronization primitives. That is what LDREX/STREX are for.
What I'd suggest in your case is to use a separate flag to indicate the second core has finished. The first core loops waiting for the flag to be cleared - with a WFE in the loop. That way if you wake unexpectedly you can see that the second core hasn;t finished yet and then go back to sleep.
Cancel
Up
0
Down
Reply
Cancel
Children
No data
More questions in this forum
By title
By date
By reply count
By view count
By most asked
By votes
By quality
Descending
Ascending
All recent questions
Unread questions
Questions you've participated in
Questions you've asked
Unanswered questions
Answered questions
Questions with suggested answers
Questions with no replies
Not Answered
Forum FAQs
0
ARM Community
977
views
0
replies
Started
5 days ago
by
Annie Cracknell
Suggested Answer
How to view SFRs in DS during debugging?
0
320
views
1
reply
Latest
1 day ago
by
Ronan Synnott
Answered
Dual-core debugging in DS
0
3173
views
2
replies
Latest
14 days ago
by
Ivan Savvateev
Answered
Failure to get an evaluation license with error Unable to execute API call /api/v1/connect
0
4112
views
3
replies
Latest
20 days ago
by
Tim Holt
Suggested Answer
DS52020.0 connection to Musca-A/B boards not working
0
Arm Development Studio
Musca-A
5147
views
4
replies
Latest
22 days ago
by
Daniel Oliveira
>
View all questions in Arm Development Studio forum