RTC with TQM823L

RTC with TQM823L

[Jean Nicollerat MD]

Hello,
I need to have an interrup every 10ms in my application running in linux.
I have a PowerPC 823 on the board TQM823L LCD from denx.
I use the ocan driver.
I try to use the RTC modules but with the code :

	fd = open ("/dev/rtc", O_RDONLY);

	if (fd ==  -1) {
		perror("/dev/rtc");
	}
	/* Turn on update interrupts (one per second) */

	retval = ioctl(fd, RTC_UIE_ON, 0);
	if (retval == -1) {
		perror("ioctl");
		//exit(errno);
	}

I get an error message :
  ioctl : invalide argument # for then line :"retval = ioctl(fd, RTC_UIE_ON,
0);"

Can somebody help ? why it is not working or a better way to get function
called each 10ms

Thanks

Jean

Re: RTC with TQM823L

[Jaap-Jan Boor]

Can't you use a cpmtimer to fire every 10ms and wakeup a
high priority thread?

Jaap-Jan

On 17-mrt-05, at 8:47, Jean Nicollerat MD wrote:

> Hello,
> I need to have an interrup every 10ms in my application running in 
> linux.
> I have a PowerPC 823 on the board TQM823L LCD from denx.
> I use the ocan driver.
> I try to use the RTC modules but with the code :
>
> 	fd = open ("/dev/rtc", O_RDONLY);
>
> 	if (fd ==  -1) {
> 		perror("/dev/rtc");
> 	}
> 	/* Turn on update interrupts (one per second) */
>
> 	retval = ioctl(fd, RTC_UIE_ON, 0);
> 	if (retval == -1) {
> 		perror("ioctl");
> 		//exit(errno);
> 	}
>
> I get an error message :
>   ioctl : invalide argument # for then line :"retval = ioctl(fd, 
> RTC_UIE_ON,
> 0);"
>
> Can somebody help ? why it is not working or a better way to get 
> function
> called each 10ms
>
> Thanks
>
> Jean
>
> _______________________________________________
> Linuxppc-embedded mailing list
> Linuxppc-embedded@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-embedded

Re: RTC with TQM823L

[Wolfgang Denk]

In message <HMECJAKDCPLOGPDHNAHECEKFCAAA.jean.nicollerat@microdev.ch> you wrote:
>
> I need to have an interrup every 10ms in my application running in linux.

This is  an  oxymoron.  Interrups  are  processed  in  kernel  space,
applications  are running in userspace. You cannot process interrupts
in aplication code.

> I try to use the RTC modules but with the code :
> 
> 	fd = open ("/dev/rtc", O_RDONLY);
> 
> 	if (fd ==  -1) {
> 		perror("/dev/rtc");
> 	}
> 	/* Turn on update interrupts (one per second) */

You mentioned you wanted signals (not interrupts) every 10  millisec,
not every second -- what exactly is it that you want?

> 	retval = ioctl(fd, RTC_UIE_ON, 0);
...
>   ioctl : invalide argument # for then line :"retval = ioctl(fd, RTC_UIE_ON,
> 0);"

Which means that the driver does not support this ioctl.

> Can somebody help ? why it is not working or a better way to get function
> called each 10ms

You can use setitimer. But be  warned.  Your  requirement  of  having
signals  every  10 milliseconds means that there is a serious problem
with your software design. You  are  doing  someting  really,  really
wrong.  To  me  it  sounds  as if you try to implement your own timer
based control loop in user space with an insane  smapp  period.  This
will  never  work  reliably (as there is no guarantee that your tasks
will be scheduled in time), and will waste a lot of CPU power.

Never take existing software  designs  from  other  operating  system
environments  and  put them without thinking into a Unix environment.
Often there are much better and more efficient approaches in Unix.


Just in case you really must stick with that 10  millisecond  raster:
in  this  case  you  will  probably have to use RTAI (especially on a
resource-limted CPU like the 823).

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de
The trouble with our times is that the future is not what it used  to
be.                                                     - Paul Valery

RE: RTC with TQM823L

[Jean Nicollerat MD]

Thanks for your answer.
I'm used to program on processor without OS. I want try linux to use linux
to have have LCD, ethernet, USB, ... , dirvers.
I have to read message that comme on the CAN bus every 2ms. Then I have to
show values on the LCD and transfers some message on the RS232.
I need a timer to the check the reception of the messages.
I seem it is difficult with linux. I will try with the RTAI.

regards
Jean Nicollerat

regards
-----Original Message-----
From: wd@denx.de [mailto:wd@denx.de]
Sent: Thursday, March 17, 2005 9:34 AM
To: Jean Nicollerat MD
Cc: linuxppc-embedded@ozlabs.org
Subject: Re: RTC with TQM823L


In message <HMECJAKDCPLOGPDHNAHECEKFCAAA.jean.nicollerat@microdev.ch> you
wrote:
>
> I need to have an interrup every 10ms in my application running in linux.

This is  an  oxymoron.  Interrups  are  processed  in  kernel  space,
applications  are running in userspace. You cannot process interrupts
in aplication code.

> I try to use the RTC modules but with the code :
>
> 	fd = open ("/dev/rtc", O_RDONLY);
>
> 	if (fd ==  -1) {
> 		perror("/dev/rtc");
> 	}
> 	/* Turn on update interrupts (one per second) */

You mentioned you wanted signals (not interrupts) every 10  millisec,
not every second -- what exactly is it that you want?

> 	retval = ioctl(fd, RTC_UIE_ON, 0);
...
>   ioctl : invalide argument # for then line :"retval = ioctl(fd,
RTC_UIE_ON,
> 0);"

Which means that the driver does not support this ioctl.

> Can somebody help ? why it is not working or a better way to get function
> called each 10ms

You can use setitimer. But be  warned.  Your  requirement  of  having
signals  every  10 milliseconds means that there is a serious problem
with your software design. You  are  doing  someting  really,  really
wrong.  To  me  it  sounds  as if you try to implement your own timer
based control loop in user space with an insane  smapp  period.  This
will  never  work  reliably (as there is no guarantee that your tasks
will be scheduled in time), and will waste a lot of CPU power.

Never take existing software  designs  from  other  operating  system
environments  and  put them without thinking into a Unix environment.
Often there are much better and more efficient approaches in Unix.


Just in case you really must stick with that 10  millisecond  raster:
in  this  case  you  will  probably have to use RTAI (especially on a
resource-limted CPU like the 823).

Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de
The trouble with our times is that the future is not what it used  to
be.                                                     - Paul Valery

Re: RTC with TQM823L

[Wolfgang Denk]

In message <HMECJAKDCPLOGPDHNAHEAEKHCAAA.jean.nicollerat@microdev.ch> you wrote:
>
> I'm used to program on processor without OS. I want try linux to use linux

That was what I expected from your posting.

> I have to read message that comme on the CAN bus every 2ms. Then I have to
> show values on the LCD and transfers some message on the RS232.

Ok.

> I need a timer to the check the reception of the messages.

No. This is fundamentally wrong. You do NOT need a timer to check  if
a device driver has data available.

This is exactly what I meant when sayin you will have to get used  to
working  in  a Unix environment., Under Unix, you will not use a time
triggered control loops which polls all your drivers,  but  you  will
use select() or poll() to wait for events from your drivers. It's the
incoming data which triggers your control loop, not a timer.

> I seem it is difficult with linux. I will try with the RTAI.

DO NOT DO IT. This will only make things worse. You are on the  wrong
track.  Don't  try to stick with a software design which does not fit
any more. Change your  design  to  take  advantage  of  the  services
provided by a Unix operating system.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de
Never call a man a fool.  Borrow from him.

RE: RTC with TQM823L

[Murray Jensen]

At 08:27 PM 17/03/2005, Jean Nicollerat MD wrote:
>I have to read message that comme on the CAN bus every 2ms. Then I have to
>show values on the LCD and transfers some message on the RS232.

Sounds like a simple device driver would handle this.

>I need a timer to the check the reception of the messages.

Could this be done by setting a timeout which you keep rescheduling?

Note that the standard clock tick on linux has 10ms resolution - i.e. 100Hz.
You might want to increase this to 1000Hz (i.e. 1ms resolution). I have read
of people doing this in this list.

>I seem it is difficult with linux.

No, its not difficult at all - its very easy. There is a learning curve 
though, just
like anything. Cheers!
                                                                 Murray...
--
Murray Jensen, CSIRO Manufacturing & Infra. Tech.      Phone: +61 3 9662 7763
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Internet: Murray.Jensen@csiro.au

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