Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.arch.embedded > #29295
| From | pozz <pozzugno@gmail.com> |
|---|---|
| Newsgroups | comp.arch.embedded |
| Subject | Re: Cortex-M: share an int between two tasks |
| Date | 2020-03-18 09:09 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <r4skvb$tkq$1@dont-email.me> (permalink) |
| References | <r4g5sc$8jr$1@dont-email.me> <r4gdi2$tn$1@dont-email.me> |
Il 13/03/2020 17:49, David Brown ha scritto:
> On 13/03/2020 15:38, pozz wrote:
>> I'm working on a Cortex-M4 MCU and using FreeRTOS.
>>
>> One task:
>>
>> uint32_t wait_period;
>> while(1) {
>> // make some things
>> vTaskDelay(pdMS_TO_TICKS(wait_period));
>> }
>>
>> The following function can be called from another task:
>>
>> void set_waiting_period(uint32_t new_period) {
>> wait_period = new_period;
>> }
>>
>>
>> In this case, is it needed to protect the access of the shared variable
>> wait_period with a mutex? I don't think, we are dealing with an integer
>> variable that should be accessed (reading and writing) atomically.
>>
>
> You don't need to use a mutex, as you won't have race conditions when
> accessing it (race conditions happen when at least one thread can be
> writing, and at least one thread reading, and the accesses are not
> atomic).
Ok, I got the point.
> However, you /do/ need to make the accesses volatile, or there
> will be no guarantee that the variable will be read or written in the
> spots where you have accessed it.
Let me explain just to be sure I got it.
If wait_period is not volatile, in the task endless loop, the compiler
could make the assumption the variable doesn't ever change, so for
example it could "cache" its value in a register. In this case, when
set_waiting_period() is called from another task, the variable in RAM is
changed, but the value in the register doesn't change, so the task will
continue using the old value.
I think the access could be volatile only in the loop and not in
set_waiting_period:
uint32_t wait_period;
while(1) {
// make some things
volatile uint32_t *vwait_period = (volatile uint32_t *)&wait_period;
vTaskDelay(pdMS_TO_TICKS(*vwait_period));
}
void set_waiting_period(uint32_t new_period) {
wait_period = new_period;
}
Back to comp.arch.embedded | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-13 15:38 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-13 17:49 +0100
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-18 09:09 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-18 09:17 +0100
Re: Cortex-M: share an int between two tasks Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-03-18 17:37 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-18 19:23 +0100
Re: Cortex-M: share an int between two tasks Les Cargill <lcargill99@comcast.com> - 2020-03-22 13:42 -0500
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-22 21:45 +0100
Re: Cortex-M: share an int between two tasks Richard Damon <Richard@Damon-Family.org> - 2020-03-22 20:50 -0400
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-23 09:09 +0100
Re: Cortex-M: share an int between two tasks Richard Damon <Richard@Damon-Family.org> - 2020-03-23 08:00 -0400
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-23 14:21 +0100
Re: Cortex-M: share an int between two tasks Clifford Heath <no.spam@please.net> - 2020-03-25 09:55 +1100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-30 16:07 +0200
Re: Cortex-M: share an int between two tasks Clifford Heath <no.spam@please.net> - 2020-03-31 09:02 +1100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-31 10:57 +0200
Re: Cortex-M: share an int between two tasks Clifford Heath <no.spam@please.net> - 2020-04-01 12:05 +1100
Re: Cortex-M: share an int between two tasks Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2020-03-30 17:49 +0300
Re: Cortex-M: share an int between two tasks kegs@provalid.com (Kent Dickey) - 2020-05-19 00:34 -0500
Re: Cortex-M: share an int between two tasks Clifford Heath <no.spam@please.net> - 2020-05-19 17:40 +1000
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-05-19 12:00 +0200
Re: Cortex-M: share an int between two tasks Tom Gardner <spamjunk@blueyonder.co.uk> - 2020-05-19 13:48 +0100
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-18 09:20 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-18 10:06 +0100
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-18 10:59 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-18 11:48 +0100
Re: Cortex-M: share an int between two tasks upsidedown@downunder.com - 2020-03-18 20:37 +0200
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-18 21:24 +0100
Re: Cortex-M: share an int between two tasks Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2020-03-19 14:05 +0200
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-19 13:16 +0100
Re: Cortex-M: share an int between two tasks Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2020-03-19 14:27 +0200
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-19 14:13 +0100
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-19 08:03 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-19 09:10 +0100
Re: Cortex-M: share an int between two tasks upsidedown@downunder.com - 2020-03-19 12:51 +0200
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-19 07:40 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-19 09:38 +0100
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-19 11:26 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-19 12:12 +0100
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-19 15:31 +0100
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-23 09:22 +0100
Re: Cortex-M: share an int between two tasks Richard Damon <Richard@Damon-Family.org> - 2020-03-23 08:10 -0400
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-23 13:47 +0100
Re: Cortex-M: share an int between two tasks David Brown <david.brown@hesbynett.no> - 2020-03-23 14:31 +0100
Re: Cortex-M: share an int between two tasks Richard Damon <Richard@Damon-Family.org> - 2020-03-23 13:50 -0400
Re: Cortex-M: share an int between two tasks Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-03-19 12:27 +0200
Re: Cortex-M: share an int between two tasks pozz <pozzugno@gmail.com> - 2020-03-19 11:45 +0100
Re: Cortex-M: share an int between two tasks upsidedown@downunder.com - 2020-03-19 13:27 +0200
Re: Cortex-M: share an int between two tasks antispam@math.uni.wroc.pl - 2020-03-18 16:24 +0000
csiph-web