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.
