newlib and time()

From	pozz <pozzugno@gmail.com>
Newsgroups	comp.arch.embedded
Subject	newlib and time()
Date	2022-09-30 08:29 +0200
Organization	A noiseless patient Spider
Message-ID	<th62c5$ufge$1@dont-email.me> (permalink)

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I often use newlib standard C libraries with gcc toolchain for Cortex-M 
platforms. It sometimes happens I need to manage calendar time: seconds 
from 1970 or broken down time. And it sometimes happens I need to manage 
timezone too, because the time reference comes from NTP (that is UTC).

newlib as expected defines a time() function that calls a syscall 
function _gettimeofday(). It should be defined as in [1].

What is it? There's an assembler instruction that I don't understand:

   asm ("swi %a1; mov %0, r0" : "=r" (value): "i" (SWI_Time) : "r0");

What is the cleanest way to override this behaviour and let newlib 
time() to return a custom calendar time, maybe counted by a local RTC, 
synchronized with a NTP?

The solution that comes to my mind is to override _gettimeofday() by 
defining a custom function.



[1] https://github.com/eblot/newlib/blob/master/libgloss/arm/syscalls.c

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newlib and time() pozz <pozzugno@gmail.com> - 2022-09-30 08:29 +0200
  Re: newlib and time() David Brown <david.brown@hesbynett.no> - 2022-09-30 09:04 +0200
    Re: newlib and time() pozz <pozzugno@gmail.com> - 2022-09-30 11:29 +0200
      Re: newlib and time() Clifford Heath <no_spam@please.net> - 2022-09-30 21:51 +1000
        Re: newlib and time() pozz <pozzugno@gmail.com> - 2022-09-30 15:32 +0200
          Re: newlib and time() Richard Damon <Richard@Damon-Family.org> - 2022-09-30 09:48 -0400
            Re: newlib and time() Clifford Heath <no_spam@please.net> - 2022-10-01 08:43 +1000
        Re: newlib and time() Don Y <blockedofcourse@foo.invalid> - 2022-09-30 11:55 -0700
          Re: newlib and time() Clifford Heath <no_spam@please.net> - 2022-10-01 08:48 +1000
            Re: newlib and time() Don Y <blockedofcourse@foo.invalid> - 2022-09-30 16:11 -0700
      Re: newlib and time() David Brown <david.brown@hesbynett.no> - 2022-09-30 14:38 +0200
      Re: newlib and time() Don Y <blockedofcourse@foo.invalid> - 2022-09-30 11:42 -0700
        Re: newlib and time() pozz <pozzugno@gmail.com> - 2022-10-03 00:09 +0200
          Re: newlib and time() Don Y <blockedofcourse@foo.invalid> - 2022-10-02 19:02 -0700
            Re: newlib and time() pozz <pozzugno@gmail.com> - 2022-12-30 17:08 +0100
              Re: newlib and time() Don Y <blockedofcourse@foo.invalid> - 2022-12-30 17:35 -0700
                Re: newlib and time() pozz <pozzugno@gmail.com> - 2023-01-04 17:09 +0100
                Re: newlib and time() Don Y <blockedofcourse@foo.invalid> - 2023-01-04 12:19 -0700
                Re: newlib and time() George Neuner <gneuner2@comcast.net> - 2023-01-04 20:12 -0500
                Re: newlib and time() Don Y <blockedofcourse@foo.invalid> - 2023-01-04 19:40 -0700
          Re: newlib and time() Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2022-10-03 10:20 +0300
  Re: newlib and time() Clifford Heath <no_spam@please.net> - 2022-09-30 17:12 +1000
  Re: newlib and time() Theo <theom+news@chiark.greenend.org.uk> - 2022-09-30 14:06 +0100

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