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Groups > comp.os.linux.hardware > #2408
| From | Jan Pieter <jp@jp.dhs.orig> |
|---|---|
| Newsgroups | comp.os.linux.misc, comp.os.linux.hardware |
| Subject | Re: Realtime clock accessible without context-switch? |
| Date | 2014-06-01 09:58 +0200 |
| Organization | Badly Configured Clients, Inc. |
| Message-ID | <lmemef$8dc$1@news.albasani.net> (permalink) |
| References | <llfapk$mhc$2@dont-email.me> <bu1qcoFt9amU1@mid.individual.net> <llhkkb$56l$1@dont-email.me> <bu46amFe2ebU1@mid.individual.net> |
Cross-posted to 2 groups.
On 05/21/2014 07:32 PM, Clemens Ladisch wrote:
> #include<stdio.h>
> #include<fcntl.h>
> #include<unistd.h>
> #include<sys/mman.h>
>
> int main(void)
> {
> int fd = open("/dev/hpet", O_RDONLY);
> if (fd == -1) {
> perror("/dev/hpet");
> return 1;
> }
> const volatile unsigned int *ptr = mmap(NULL, 4096, PROT_READ, MAP_SHARED, fd, 0);
> if (ptr == MAP_FAILED) {
> perror("mmap");
> return 1;
> }
> printf("frequency: %.5f MHz\n", 1e9 / ptr[1]);
> for (;;) {
> printf("\rcounter: %08x", ptr[60]);
> fflush(stdout);
> usleep(123456);
> }
> }
as user:
/dev/hpet: Permission denied
as root:
/dev/hpet: Device or resource busy
Jan Pieter.
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Realtime clock accessible without context-switch? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-20 10:29 +0000
Re: Realtime clock accessible without context-switch? Clemens Ladisch <clemens@ladisch.de> - 2014-05-20 21:56 +0200
Re: Realtime clock accessible without context-switch? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-21 07:29 +0000
Re: Realtime clock accessible without context-switch? Thomas Richter <thor@math.tu-berlin.de> - 2014-05-21 09:47 +0200
Re: Realtime clock accessible without context-switch? William Unruh <unruh@invalid.ca> - 2014-05-21 15:51 +0000
Re: Realtime clock accessible without context-switch? Clemens Ladisch <clemens@ladisch.de> - 2014-05-21 19:32 +0200
Re: Realtime clock accessible without context-switch? Richard Kettlewell <rjk@greenend.org.uk> - 2014-05-21 23:35 +0100
Re: Realtime clock accessible without context-switch? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-22 07:53 +0000
Re: Realtime clock accessible without context-switch? Clemens Ladisch <clemens@ladisch.de> - 2014-05-22 20:36 +0200
Re: Realtime clock accessible without context-switch? Richard Kettlewell <rjk@greenend.org.uk> - 2014-05-22 20:26 +0100
Re: Realtime clock accessible without context-switch? William Unruh <unruh@invalid.ca> - 2014-05-22 22:48 +0000
Re: Realtime clock accessible without context-switch? Jan Pieter <jp@jp.dhs.orig> - 2014-06-01 09:58 +0200
Re: Realtime clock accessible without context-switch? Todd <Todd@invalid.invalid> - 2014-05-23 14:20 -0700
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