Yup, looks like we need some "common and alternative solution for smaller platforms" that would provide small versatile problem free implementation that would still provide 64-bit time? Maybe a library or module? So that we have long long int64_t time by default that would provide POSIX compliance, but may have different implementation for smaller platforms? :-)
I am for going with this change, it should work on smaller platforms too, and then when needed we may work out better dedicated common implementation for smaller platforms? :-) -- CeDeROM, SQ7MHZ, http://www.tomek.cedro.info On Mon, May 4, 2026 at 1:42 PM Nathan Hartman <[email protected]> wrote: > > Regarding SDCC, ZDS, weird compilers that can't handle POSIX definitions: > that's a different situation than the time_t issue: NuttX is written in C89 > and therefore must be compiled with a conforming C89 compiler. You can't > compile NuttX with, say, a Pascal compiler or a Fortran compiler, and you > can't compile it with something that looks similar to C but isn't. It has > to be a proper C compiler that understands C89. > > In contrast, the time_t issue is a user choice. We don't lose strict POSIX > compliance because we will use 64-bit time_t out of the box. But we give > developers a way to make compromises when they decide it makes sense. > Example: a toaster shouldn't need a big powerful MCU. 8-bit MCU should be > plenty. And you're not going to toast a piece of bread for more than 50 > days. Maybe 50 seconds max. And if you're mass producing toasters, saving a > few cents per MCU by choosing one with less flash and RAM will save a lot > of money. So in this case the developer may decide that time_t should be > reduced because it makes sense. > > Again, out of the box, we will be POSIX compliant with 64-bit time_t. > > Nathan > > On Mon, May 4, 2026 at 9:05 AM Gregory Nutt <[email protected]> wrote: > > > > > > > > > ________________________________ > > *Hobbyists are valued users of the OS including retro computing hobbyists > > and DIY “Maker” hobbyists.* > > - > > > > *Supported toolchains: GCC, Clang, SDCC, ZiLOG ZDS-II (c89), IAR. Others?* > > I think we all agree that time_t 64-bit is very important and should be the > > default, but we cannot leave behind old MCUs and users because of it. (that > > is what "All Users Matter" means) > > > > But what if this is conflicts with > > > > ## Strict POSIX compliance > > > > Support for SDCC and ZDS where not removed, just broken irreparably. > > Those compilers (and other small system compilers) will not support POSIX > > interface definitions. One problem is that you cannot pass structures or > > even enumeration values as parameters. There used to be special case > > definitions (not so different from what we are talking about here) to make > > the OS interfaces non-POSIX so that these tools could build NuttX. The > > change was very invasive and turned me into the believer in very strict > > POSIX interface definitions. > > > > This case it was a painful trade-off. > > > > As a point of clarification... those changes were made PRIOR to the > > INVIOLABLES.md. The starting point really should be sometime after that. > > From the standpoint of the INVIOLABLES.md, those architectures and tools > > were never supported. > > > > Otherwise we can change our motto to Linus Torvalds' phrase: "Doers > > decide!" (probably he got it from "Parable of the Sower" book) > > > > So let me disagree with my colleague raiden00: "NuttX is for All Users" and > > "All Users Matter" :-) > > > > BR, > > > > Alan > > > > On Mon, May 4, 2026 at 9:07 AM Nathan Hartman <[email protected]> > > wrote: > > > > > One of the nicest things about NuttX is that you can use it with any > > > microcontroller. That's the biggest selling point for me: instead of > > using > > > a different set of vendor libraries for each microcontroller, you can > > > standardize on NuttX and your code becomes portable across > > microcontrollers > > > regardless of vendor. > > > > > > If we start leaving microcontrollers behind, first it will be 8-bit > > > microcontrollers, then likely it will be 16-bit, eventually we'll be a > > > large and heavy OS that only works on powerful, expensive chips. > > > > > > I like the idea of 64-bit time_t being the default with a way to reduce > > it > > > when appropriate for a particular use case. The Kconfig "---help---" text > > > could warn that less than 64-bit is non-POSIX and the consequences of > > using > > > less than 64 bits, and let the developer decide. By default we'll be > > > 64-bits and complying with POSIX on this issue. > > > > > > My 2¢... > > > > > > Nathan > > > > > > On Mon, May 4, 2026 at 7:43 AM Alan C. Assis <[email protected]> wrote: > > > > > > > I wasn't aware that libfaketime was facing an issue with the time_t > > > moving > > > > to 64-bit ? > > > > > > > > https://github.com/wolfcw/libfaketime/issues/418 > > > > > > > > I think in our case we don't have any issue (I hope), other than the > > code > > > > increasing and a worse performance on 8/16/32-bit MCUs. > > > > > > > > BR, > > > > > > > > Alan > > > > > > > > On Sun, May 3, 2026 at 4:22 PM Gregory Nutt <[email protected]> > > wrote: > > > > > > > > > There are some compilers that do not support uin64_t natively. For > > > > those, > > > > > library support would be needed. > > > > > > > > > > If an implementation requires multiple accesses to read/write uint64, > > > > then > > > > > the accesses would be non-atomic. At a bare minimum, the locked > > > section > > > > > would be required (which would not prevent concurrent accesses from > > > > > interrupt handlers). > > > > > > > > > > I support the POSIX first prioritization. I removed a lot of support > > > > > needed by some of these architectures in the past for similar > > reasons. > > > > > That broke certain compilers and a lot of implementations (which are > > > > still > > > > > broken). We should probably do the same, but with full awareness of > > > > > functionality well will use or things that are very broken. > > > > > > > > > > I have suggested removing support for the 8 bit architectures and for > > > > > compilers like the ZDS and SDCC compilers. Carrying architectures > > with > > > > > this level of breakage is misleading. > > > > > > > > > > ________________________________ > > > > > From: [email protected] <[email protected]> > > > > > Sent: Sunday, May 3, 2026 9:42 AM > > > > > To: [email protected] <[email protected]> > > > > > Subject: Re: [DISCUSS] Removal of CONFIG_SYSTEM_TIME64 and make > > time_t > > > > > 64-bit by default > > > > > > > > > > Hello, > > > > > > > > > > I tried for AVR128DA28 - tools/configure.sh -l breadxavr:nsh > > > > > > > > > > Default setting (CONFIG_SYSTEM_TIME64 not set): > > > > > > > > > > Register: nsh > > > > > Register: sh > > > > > LD: nuttx > > > > > Memory region Used Size Region Size %age Used > > > > > flash: 50457 B 128 KB 38.50% > > > > > sram: 636 B 16 KB 3.88% > > > > > eeprom: 0 B 512 B 0.00% > > > > > rodata: 592 B 4 KB 14.45% > > > > > CP: nuttx.hex > > > > > CP: nuttx.asm > > > > > > > > > > With CONFIG_SYSTEM_TIME64 set: > > > > > > > > > > Register: nsh > > > > > Register: sh > > > > > LD: nuttx > > > > > Memory region Used Size Region Size %age Used > > > > > flash: 52307 B 128 KB 39.91% > > > > > sram: 668 B 16 KB 4.08% > > > > > eeprom: 0 B 512 B 0.00% > > > > > rodata: 592 B 4 KB 14.45% > > > > > CP: nuttx.hex > > > > > CP: nuttx.asm > > > > > > > > > > 2kB seems quite noticeable for a chip with 128kB flash. Runtime costs > > > > > are somewhat hard to assess, the time_t type is used in internal > > > > > timekeeping but the code was developed with tickless mode of > > operation > > > > > in mind so the timekeeping functions should not run that often unless > > > > > the system gets busy with processing lots of timed events. > > > > > > > > > > As for the benefits - the real question is how many devices (designed > > > > > with a chip like this one) need to know real time and therefore > > handle > > > > > year 2038. (None of my use cases need that.) > > > > > > > > > > So for small systems, having the option to configure NuttX so time_t > > is > > > > > 32 bit wide would certainly be beneficial. Making the SYSTEM_TIME64 > > > > > option default to DEFAULT_SMALL would be nice but it's not > > > POSIX-correct > > > > > so I don't think that's gonna fly. > > > > > > > > > > > > > >
