Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.arch.embedded
Subject: Re: 32 bits time_t and Y2038 issue
Date: Tue, 11 Mar 2025 17:32:03 +0100
Organization: A noiseless patient Spider
Lines: 85
Message-ID: <vqpoi3$226ih$1@dont-email.me>
References: <vqpkf9$1sbsa$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Tue, 11 Mar 2025 17:32:04 +0100 (CET)
Injection-Info: dont-email.me; posting-host="e5a3c6d3de234e8734c5c12995df05a2";
	logging-data="2169425"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX19R1y59/HHiG8GID2gxeC/lHT6S26FVt+U="
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.11.0
Cancel-Lock: sha1:fjHB5MteaY6cQ/wo7vL80C4d7LY=
In-Reply-To: <vqpkf9$1sbsa$1@dont-email.me>
Content-Language: en-GB
Bytes: 5116

On 11/03/2025 16:22, pozz wrote:
> I have an embedded project that is compiled in Atmel Studio 7.0. The 
> target is and ARM MCU, so the toolchain is arm-gnu-toolchain. The 
> installed toolchain version is 6.3.1.508. newlib version is 2.5.0.
> 

I /seriously/ dislike Microchip's way of handling toolchains.  They work 
with old, outdated versions, rename and rebrand them and their 
documentation to make it look like they wrote them themselves, then add 
license checks and software locks so that optimisation is disabled 
unless you pay them vast amounts of money for the software other people 
wrote and gave away freely.  To my knowledge, they do not break the 
letter of the license for GCC and other tools and libraries, but they 
most certainly break the spirit of the licenses in every way imaginable.

Prior to being bought by Microchip, Atmel was bad - but not as bad.

So if for some reason I have no choice but to use a device from Atmel / 
Microchip, I do so using tools from elsewhere.

As a general rule, the gcc-based toolchains from ARM are the industry 
standard, and are used as the base by most ARM microcontroller 
suppliers.  Some include additional library options, others provide the 
package as-is.  For anything other than a quick demo, my preferred setup 
is using makefiles for the build along with an ARM gcc toolchain.  That 
way I can always build my software, from any system, and archive the 
toolchain.  (One day, I will also try using clang with these packages, 
but I haven't done so yet.)

Any reasonably modern ARM gcc toolchain will have 64-bit time_t.  I 
never like changing toolchains on an existing project, but you might 
make an exception here.

However, writing functions to support time conversions is not difficult. 
  The trick is not to start at 01.01.1970, but start at a convenient 
date as early as you will need to handle - 01.01.2025 would seem a 
logical point.  Use <https://www.unixtimestamp.com/> to get the time_t 
constant for the start of your epoch.

To turn the current time_t value into a human-readable time and date, 
first take the current time_t and subtract the epoch start.  Divide by 
365 * 24 * 60 * 60 to get the additional years.  Divide the leftovers by 
24 * 60 * 60 to get the additional days.  Use a table of days in the 
months to figure out the month.  Leap year handling is left as an 
exercise for the reader (hint - 2100, 2200 and 2300 are not leap years, 
while 2400 is).  Use the website I linked to check your results.

Or you can get the sources for a modern version of newlib, and pull the 
routines from there.


David


> In this build system the type time_t is defined as long, so 32 bits.
> 
> I'm using time_t mainly to show it on a display for the user (as a 
> broken down time) and tag with a timestamp some events (that the user 
> will see as broken down time).
> 
> The time can be received by Internet or by the user, if the device is 
> not connected. In both cases, time_t is finally used.
> 
> As you know, my system will show the Y2038 issue. I don't know if some 
> of my devices will be active in 2038, anyway I'd like to fix this 
> potential issue now.
> 
> One possibility is to use a modern toolchain[1] that most probably uses 
> a new version of newlib that manages 64 bits time_t. However I think I 
> should address several warnings and other problems after upgrading the 
> toolchain.
> 
> Another possibility is to rewrite my own my_mktime(), my_localtime() and 
> so on that accepts and returns my_time_t variables, defined as 64 bits. 
> However I'm not capable in writing such functions. Do you have some 
> implementations? I don't need full functional time functions, for 
> example the timezone can be fixed at build time, I don't need to set it 
> at runtime.
> 
> Any suggestions?
> 
> 
> [1] 
> https://developer.arm.com/-/media/Files/downloads/gnu/14.2.rel1/binrel/arm-gnu-toolchain-14.2.rel1-mingw-w64-i686-arm-none-eabi.zip